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Bus Discussion => Bus Topics ( click here for quick start! ) => Topic started by: brettpearson67 on May 31, 2020, 03:38:05 PM
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Was wondering if anyone has tried running coach ac with another compessor(electric) while engine is off?
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Seems like running the huge HVAC air handler fan would use as much or more power than the compressor.
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It's a DC motor so if you want to run it slower just supply less voltage.
Jim
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I'm picking up a DL3 this week and thought that there might be a way to switch to an electric compessor while parked, rather than replace it with rooftops or minsplits or basement hvac. Especially since it is still working great.
Maybe even some sort of ac motor powering the coach compressor? Is there such a thing as a "dual fuel" compressor, so to speak?
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The only eagle 25 built had an AC system like that. The last time I saw it at the poor excuse for a factory it was working. I have not seen the bus or have heard if the system is working. I don't know what size the system was.
Wayne
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It seems like the coach compressor is maybe 16-18 tons. HP requirements of 12-14. doable with a 240 volt power supply. Although I dont know that the requirements wouldn't be less for an electric motor, as torque specs are different?
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I didn't know anybody had done it but that is my plan eventually. I don't think it is too practical to try to drive the original compressor with an electric motor, both because newer sealed compressors are more efficient and because the drive would likely be both impractical and inefficient. But there is no reason a sealed compressor could not be plumbed in parallel to the original. What size to use is the question. My thought was that you might be able to get by with running two smaller sealed compressors, making it more versatile for if you had 30 or 50 amp service. Run one or both depending on power available.
Jim
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I’m waiting for my HVAC friend to get back to me to talk about sizing the compressor/s
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It will be interesting to see what he has to say.
Jim
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So this was one of my first thoughts also. I asked on an HVAC form I belong to about running a electric compressor in parallel.
As I understand the OTR HVAC system is much larger then typically required because its harder to heat or cool the bus while its in motion. So I want to know, how big is the system now, and could a smaller compressor providing 24K-36K be feasible using the same condenser and evap.
One Idea I had was to replace the current belt driven compressor with an A/C generator. 240V 10KW. And then use the existing system with a 240V compressor and fans.
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You could consider one of these run by an electric motor. GM used two of these in 4905's as an option inplace of the big V york compressor. Might need a large motor though. You also will need lots of current to run the condenser fan and blower motors.
https://www.hemmings.com/stories/article/frigidaire-a-6-air-conditioning-compressor
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Maybe you could use a couple of these:
https://ordering.fwwebb.com/woitem/437290*1?CAWELAID&gclid=CjwKCAjw8df2BRA3EiwAvfZWaMuXio9wJ7zPZet5FrsR6i5beX37E8xLPLwtLEhZ90JTL5cet5XqjBoC3UsQAvD_BwE
Heating & Cooling Refrigeration Compressors
Copeland ZP24K5E-PFV-800
Compressor ZP Scroll 208/230 Volt 1 Phase R-410A 24000 BTU Polyol Ester
More Images & Video
$547.25 / ea
Qty
Guests: In Stock. Ships in 1 Business Day.
Specification Sheet
Or, depending on the current demands, maybe two or three 3 ton units and stage them in as needed, leave the engine driven compressor alone, and use it OTR as intended. They do have intake and exhaust valves that will prevent backflow. (Might need check valves with the scroll compressors.)
The 102DL3 has 13 tons of on board air at least. Depending on how you add it up, it could be as much as 14 tons.
Jim
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Seems to me that it MIGHT be more cost effective and easier to simply put in a mini split.
The Bus Grease Monkey has replaced both his rooftops with a single min split that he says can cool his bus to the point of being uncomfortably cold. AND he runs his off batteries.
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There is nothing magical about a mini-split other than the new ones using the more efficient type of compressors. Fans being fans and motors being motors, there is a limit as to what is to be gained by changing the air movers. Yes the OTR units are large but it doesn't mean they have to be run at full speed. Their efficiency at lower speeds may be less... or it may not. And, pwm drives are available cheap to boost the efficiency.
What we really want to know is how many amps does it take to start and how many to run a given size compressor in terms of amps per btu. The lower that ratio is, the higher cooling we can achieve from a given shore line. It is likely that ratio is rather closely tied to seer rating, and seer ratings have gone up dramatically in the last 20 years. So the first thing is to upgrade the compressor. The largest one that the shore line will support should be the objective here but soft-start will prove a clear advantage, possibly dropping the amperage draw to the point that is is only necessary to delay the air fans until the compressor is up to speed to even out the current draw and leave some margin.
Jim
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The huge elephant in the room, is WASTED HVAC...
The mini-splits have rapidly proven that roof airs are total garbage and lies, when it comes down to the effect of their operation on the inside temp.
Up in that box on the roof is some very sad chunks of cheap white styrofoam, poor attention to heat/cold transfer between inside/outside and the heat producing parts. The cold is being stolen up in the box.
Sure, the PARTS may be 12k worth of cooling, but an RV never gets anywhere near 12k of cooling down below.
The minisplit keeps all the hot outside, and all the cold inside, so the effective "cold" out of parts that are rated at the same 12k, is much better.
The elephant in the room for using the stock HVAC is air intrusion, and having to keep cool all those surfaces of the air distribution system, that don't contribute to interior cooling.
Grease Monkey isn't the source i would be using for my information.
Happy coaching!
Buswarrior
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I am waiting for the day someone builds a split unit outside unit made to mount on it's side so the air vents up and then the line set could go inside to the head unit where ever you wanted to put it .
the seer on the newer units is way up there and the amp draw is very low so one could put 3-4 units up on the roof and have more a/c then you would ever need with out a problem of large amp draw
how hard could it be maybe we just need a bus nut to build it
dave
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Use a setup like this: https://www.alpinehomeair.com/viewproduct.cfm?productID=453078036
You could remount the compressor and lay this down flat. The compressor is the only part that would not like being on its side. In my case the current air flow actually works. Although backwards from the OTR system because the air will vent out the side and come in through the bottom. I could take the condenser off the door and mount the mini split in its place. I am going to check the dimensions.
The air handlers can be mounted under the floor. I would probably run return air from one side and vent air on the other side to create circulation. I could add some hydronic heat exchangers on the intake side with valves to use engine heat to heat the bus. Place the air handler in fan mode and circulate the heat.
There are 3 of these to one condenser you can actually have up to 5 I think with this brand. That kit has 3X 12K concealed duct units. Evenly spaced with an extra duct off the front one to the drivers area for A/C and defrost.
Again, the OTR compressor could then easily be replaced with a large generator to power the unit over the road and/or Charge Batteries for an off grid system. They run off inverters nicely.
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"Grease Monkey isn't the source i would be using for my information."
Well, I'm sure there are better sources except that
"he's been there and done that".
And that's where "I" would be looking.
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"Grease Monkey isn't the source i would be using for my information."
Well, I'm sure there are better sources except that
"he's been there and done that".
And that's where "I" would be looking.
People have done it long before the grease monkey Yvan has been doing it for 2 years with Ion batteries anyways bring those suckers to AZ in a 112 F heat and give them a test bet you cold one he would uncomfortably hot
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Do the coach ac units work well in 115 degree heat?
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they do ok the condenser, fans and dc motors are large enough to draw enough air over the condenser to keep the head pressure in check some of the buses have 2 of the big @$# DC motors running fans ,lol but a 10,000 but mini split will not keep a bus cool here
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We have been running a single 13500 btu roof top ac on our one & only bus for over 40 years now. The bus has full timed us in every type of environment including 115° desert heat. The word successfully has more to do with the owner(s) than the equipment IMO. When our bus is at 85° interior temp during 115° ext. Temps - that is perfectly fine with us so in our opinion our setup is fine. Catch our drift... 8)
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The average temp drop here with standard AC is 22 degrees unless you have a unit large enough to over power the heat lol when we hit a 122 degrees our unit really works and it shows on the power bill all the units here are oversized I have 6 tons where in Idaho our house was 2 story and more sq ft and a 3 ton unit did fine,it nothing to see a house here with out 2 or 3 units.Our rv has 3 15.000 btu units and well insulated 2 will freeze you but sometimes I need to run all 3 to drop the temperature in a hurry so 1 or 2 units can keep up
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The mini-split separates the hot side from the cold side. So does every other well designed system. So does the OTR air, so do standard residential units.
The mini-split is ductless. But this may not be that great of an idea. Sure, you don't have to cool the ductwork but that generally doesn't add much of a heat load and gives way better distribution of the cold air.
The mini-split is smaller. But newer units are now at 3 tons and more. That is well into the residential range.
So let's face it, the only real advantage the mini-split might have is packaging and that is questionable.
You could just as well call the OTR system a Maxi-split. Except that it has air distribution ducting that the mini-split lacks. It also has a much larger condenser than you will ever see on any mini-split system, and the limiting factor in any AC system is the ability to get rid of heat. The large condenser is not a limitation, to the contrary it is a huge advantage. So I really don't understand the push to throw it out and replace it with something that doesn't have a hope in hell of ever doing as good of a job.
I do get that is looks simpler. Looks. Not the same as being.
Jim
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So let's face it, the only real advantage the mini-split might have is packaging and that is questionable.
From what I gather the newer mini-splits are measurably more efficient than rooftops. Those pioneering full off-grid electric source seem to indicate they consume less energy.
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The problem with the factory otr is the engine has to be running, and in my case at high idle or moving to actually work. So the question is add ac power to the factory or replace it with something that works all the time. Mini split and ductless are two different things. You can get ducted minisplits.
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There's a real good reason why the studio buses use 5 roof top A/C's-because they work and are simple to replace. Just install 3 rood tops and be done with it. I have 3 on my 40ft'r and usually 2 do the job just fine. Good Luck, TomC
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If a regular mini-split doesn't work for you, it's also possible to do like Custom Coach did and build your own. They used off-the-shelf commercial refrigeration components to build their systems, using a Copeland compressor and a condensing unit down in the bay, and an evaporating coil/fan upstairs. The added ducting to some, as needed.
These compressors can be bought in many sizes and capacities.
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Richard, that's exactly what I've been trying to tell these guys. A good Copeland compressor is guess what? The exact thing they use in mini-splits.
You already have the best condenser you will ever find sitting right there in the side of the bus. It's only job is to cool down the compressed gas going through it and for that, bigger is most certainly better. As long as there is no resistance to the freon flowing through it it is as efficient as it can ever get.
On the evaporator side, the TXV controls how much liquid goes in and therefore how much cooling. All the evaporator does is trade that for heat. If it is too small it will freeze up. If it is too big? What? How can it be too big? The only consideration here is making sure the TXV will never flow more liquid than the condenser puts out, and that's a function of the compressor. Lines are lines. Bigger ones flow more and do it easier but hold more. The only thing that leaves for efficiency improvements are to prevent heat losses (or cold). So good insulation and separation in the right spots. As BW said, roof air units will never come close to matching one where the evaporator is separated out. That's why residential units are made the way they are.
And now with ducted mini-splits, when compared to the existing maxi-split where is the efficiency advantage? All you are doing is comparing an efficient small system to an efficient larger system.
With a Copeland and a little plumbing you have the option of configuring the system as you choose and making it switchable. Solenoid valves in the right places and multiple compressors along with TXVs on the main evaporator that can be switched in and out to match the compressor would let you have a fully configurable system for anywhere from 3 tons or less clear up to the full system capacity of 14 tons in stages.
That's a more complex system but each aspect is simple. You have two 1-1/2 ton evaporators in the bins so that's 3 tons and each one already has it's own properly sized TXV. So add a solenoid valve to shut off flow to the main evaporator (if there isn't one already), add in a parallel Copeland past the belt driven compressor, and voila! You have your 3 ton system. Put a PWM driver on the condenser fan with a thermocouple or other temp senser so that it only works hard enough to get rid of as much heat as it needs to and you have your efficient 3 ton AC system.
It shouldn't be hard to sort out how you go up from there. You have a driver's evaporator rated for 1 ton (but it is fitted with a 1-1/2 ton TXV so you should be able to get more out of it) and then the main 10 ton evaporator. You could easily run that one at 5 tons by switching in a 5 ton TXV with a solenoid valve or two. I don't understand why some guys try to make it so hard to understand. But I guess that's business.
Jim
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AC and refrigeration units are simple to build they all start with a compressor,what he trying to do using the engine driven compressor then driving it by electricity is going to take some thought out planning .I don't think a sealed compressor like Copeland could handle the oil charge reqired for the Carrier bus system
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That's a valid concern. The oil would have to be compatible for both but there is probably an oil that is, and it could be the one already being used. Generally the compatibility problem is with the refrigerant rather than the compressor. Also, most of the oil stays in the compressor, with only a small amount being dispersed in the lines. But I think what you mean is the risk of flooding the Copeland with oil maybe? Causing compressor stall? If it is a problem maybe it could be controlled by line routing to the Copeland and perhaps an accumulator dumping into the main compressor if needed. Then again, it might work just fine without it.
Jim
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My biggest problem with the factory system it the noise. It's really loud. I like the idea of building a custom system using what's there. Hardest part would be controlling everything. Switching valves to isolate each Compressor. My bus has R438a as a replacement for the r22.
I like the idea of several different zones in the bus though. Save more power if running on batteries/solar by only cooling/heating the area in use.
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It definitely is somewhat complicated, but my original thought was using parallel compressor/s. I think that if we can just add those in with the necessary controls, rather than chucking a functional system already in place, that would be pretty efficient.
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That was my thought too. I'm fortunate in that my system uses r134 and it works. I have no immediate plans to tear into it as I'm working on other parts of the conversion and will be for awhile. But the time will come.
For the condenser fans, I'd try a pair of these:
https://www.ebay.com/itm/Motor-Governor-Speed-Regulator-PWM-Controller-10-50V-100A-5000W-Reversible-DC/224027378561?_trkparms=aid%3D555021%26algo%3DPL.SIMRVI%26ao%3D1%26asc%3D20190711100440%26meid%3D963d9a736e1743d28e1a7985b8ce6c3c%26pid%3D100752%26rk%3D4%26rkt%3D17%26mehot%3Dco%26sd%3D183579225779%26itm%3D224027378561%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplRVIAMLv5WebWithPLRVIOnTopCombiner&_trksid=p2047675.c100752.m1982
Along with a thermostat of some type, maybe with a programmable output. This could be the tricky part really, just finding a suitable thermostatic controller that can output a signal compatible with the PWM controller's requirements. Usually a 0-5v signal works.
The motors can draw up to 90A at 27.2 vdc which is 2450 watts. Divided by 240v that's about 10 amps disregarding power factors and suchlike. So basically a 10 amp draw at full tilt 'n boogie. My motors (original from appearance) show 62A on the name plate so that is 124A total at max, or about 15A at 220v. The main evaporator fan can draw up to 70A@27.2vdc, so 1900w and 8A respectively. Mine, a 2018 replacement is rated at 1.4hp and 45A or about 5-1/2A. Which should tell us that new motors can drop power requirements here by about 1/3 at least.
Noise is directly rated to fan speed, and with the size of the condenser and the expected cooling requirements, condenser fan speed can be considerably slower than max. 25% or less might be a good working range and the current needs drop accordingly. so instead of squandering 20A or more on the fans you may be able to get by in the 4-5A range and I'd expect that to be acceptable.
Jim
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I wanted to circle back to this as I have learned a lot more about the OTR system.
One of the issues raised is oil, The bus compressor uses a 68 weight oil. I replaced mine with POE oil and so far so good. I think a lot of compressors use 32 weight but 68 is common enough it was on the shelf at a local HVAC supplier.
I think the best option is to use one or the other. Since we know the Fan motors are not very efficient I would go ahead and replace them with 220V motors. And replace the compressor with something in the 32000 - 48000 btu range.
One thing to remember is the A/C in the bus was sized for a full sun load on the windows and 40+ Bodies inside a tin can. So when we run the 3-4 people in the bus with half the windows taken out and the other half covered with curtains I dont think we put anywhere near the load the system was meant to handle.
Stick the a R22 compressor and fill it with 407C so you dont have to replace TXVs or metering devices.
Use Variable Frequency Drive Controllers for all the motors, fans and compressor. And a 8000W inverter to power it all. Use 2 batteries to make a load buffer so the charging system does not get spiked. The DN50 alternator is rated for 250A@24V There is a + version that will offer 450A@24V. But realistically with the VFDs setup to soft start all the motors, and a sequencer to prevent them from starting at once I think you could keep the surge under 200A. and Continuous under 150A.
And you would be no more then 36A off shore power. Probably less then 20A running. 30A surge.
That would be one AC system that can run off the engine, batteries, solar, gen, or shore power. You could sell the old compressor for the cost of the new components. And if you really wanted, add a second DN50+ with a belt drive where the compressor was for some extra charging power and add more batteres for an off grid setup.
It looks like the carrier compressor runs 2.9 - 9.2 tons. Based I assume on engine speed. I think this is another reason the system is so massive, it need to keep the bus cool at an idle when the compressor is only putting out 2-3 tons of refrigerant flow. I think a 3 ton compressor would be plenty. Ducting would require some thought. Noise I think would be greatly reduced by the AC motors, yes air is a lot of the noise, but those DC motors are not quiet ether. Better blower fans might help too. I know mine need to be balanced.
If time or money allows I plan to try to make use of some of the old system to make a newer system.
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GM A-6 compressor is very versatile for build your own system.
https://www.hemmings.com/stories/article/frigidaire-a-6-air-conditioning-compressor
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GM A-6 compressor is very versatile for build your own system.
https://www.hemmings.com/stories/article/frigidaire-a-6-air-conditioning-compressor
I am trying to get away from engine driven. My goal would be one contained electric unit that can be powered from any source.
A small idea of the parts I would use:
Compressor:
https://www.supplyhouse.com/Copeland-ZR42K5E-PFV-800-1-PH-R407C-Compressor-42800-BTU-208-230V
VFD:
https://www.amazon.com/Variable-Frequency-Controller-Converter-HUANYANG/dp/B077KS9LRY?ref_=fsclp_pl_dp_6
Inverter:
https://www.ebay.com/itm/8000W-LF-SP-PURE-POWER-INVERTER-DC24V-AC220V-110V-Battery-Charger-ATS-UPS-10-0V/391958860740?epid=11032780109&hash=item5b429193c4:g:0g4AAOSwBuVezGMI
The VFD would do a slow ramp up to the full compressor power when it gets an input on one of the universal I/O pins. I would build a custom thermostat that would drop the compressor and fans to ~50% when the set temp is reached. and then down to ~25% at 2 degrees under and off at 4 degrees under. Realistically I would try to find the temperature curve to have the system run continuously to maintain the temperature within a degree or 2.
Now I just need to win the lottery or find someone that wants to fund this idea :D
For now I really like the mini splits. I may if I have time customize the condenser to take up less space. But otherwise I am just going to enjoy it as is.
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The A6 was eventually replaced by the Sanden and larger displacement units are available. They are widely believed to be more efficient... but I think they are just lighter in weight. The old A6 was a bit hefty. Both have pretty much eliminated the York which was a standard inline piston compressor and a source of vibration. The same could be said for the OEM compressor, though it's a V configuration. The axial designs do have some advantages.
I think your analysis of heat loads is pretty close to the mark and around 3-4 tons would probably do the trick. Interesting that the Carrier compressor tops out at 9.2 whereas the main evap has a 10 ton txv. This sort of tells us that less than 10 T is both available and required, and that it can be allocated as desired. It also tells us that the TXV's can operate with as little as 25% of max fluid flow under full demand. Hey Bus Warrior, how well did those D series cool when they sat and idled in the hot sun? As they aged did that go away? Inquiring minds and all that.
What I'm taking away from this is that the existing system might work quite well with a 3-4 ton scroll compressor and no other major changes. Although some PWM drives and a VFD on the compressor wouldn't go amiss. I'm not sure the fan motors are all that inefficient. Just large. That means inertia, but at steady speed that shouldn't be costly. Just set the PWMD to move the required minimum of air, perhaps with a thermostatic controller. It'll reduce the noise factor too.
Jim
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9.2 is the mid range, but the way it is driven from the motor I dont see it getting much beyond that. It I think 17 was the high range but that was at 8000 RPM. Its only putting out 4 at 2000RPM which is probably an average cursing RPM. I dont have a tach so not totally sure.
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So we'd need to know if it is overdriven, but hey, I just looked at it and if anything it is probably a little underdriven. So probably 3-4 ton is probably just about right.
Jim
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No overdrive, the pulleys look like 1:1 or maybe a little slower. I am going to keep an eye out for a deal on an old R22 A/C or mini split I can pull parts from.
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$795 just for the compressor? What is the vehicle you are putting this in?
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Mci 102A3
Thats new retail. I would buy a reman or overstock.
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One A-6 compressor can keep our bus cold as we want. For buses sold in hot climates there was an option to have two of them, which I'm sure would have really cooled well.
The a/c unit on the Freightliner sleeper cab is powered by the battery bank between the rails. It was about 95F outside today, and the inside of my sleeper stayed comfortable at about 68F all day. It will freeze me out overnight if I turn it to max.
Don't know the exact type of compressor they use on this sleeper, but I'm sure that it's a style that could be put to use in a bus. The outside coil/fan is mounted on the rear of the sleeper, and it would be really easy to install it on a bus.
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One thing to keep in mind is that every time you convert from one type of power to another you lose energy in the conversion, and not just electrical to mechanical either. For instance, in changing from 24vdc to 220ac there is a conversion cost. It may not be as much as in other forms of conversion but it does add up. Therefore, going from your solar cells to battery is one, from battery to household is another, and the batteries themselves have a loss, there is a loss through the solar controller, and then of course a loss at the device using the power, just for examples.
Jim
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In 100 degree heat, Washington DC, one summer, it took all the old school tricks to keep a DL model acceptable waiting for the church group of seniors.
It was struggling when on the fast idle. Driving, it caught up fine.
Find a big enough parking lot and head for the back, park bum to the sun, no sun load on windows, fresh air closed up, all of it running on high, main, driver's and parcel racks, all overhead gaspers open.
Dangerous game, when an idling ticket cost $300 in those days.
Happy coaching!
Buswarrior
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Good info.
So if the compressor puts out 4 tons at 2000rpm my guess would be half that at idle maybe? It sounds like the compressor might have been seriously undersized for the rest of the system which hardly makes any kind of engineering sense that I can see. It leads me to question either the output specs of the compressor, the cooling requirements of the coach, or both.
Jim
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Go ask Carrier?
It's their systems, they'll know why they did whatever they did.
Happy coaching!
Buswarrior
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Go ask Carrier?
It's their systems, they'll know why they did whatever they did.
Happy coaching!
Buswarrior
Carrier made the compressor and I think the condenser. The Evaporator was a different company and most of the other parts. Carrier did not design the system, MCI did.
I am thinking the TXVs and compressor are sized to work well (Not Effeciently) at running speed without failing at high speed. Maxed out going up a hill I could see the RPMs getting high enough to get 10 ton out of the compressor. Infact when I do the compressor stops due to high pressure and I get an A/C Malfunction light, usually just before 4th gear on a slight incline. I think this was due to the MO99 that had replaced the R22. Since the 407C it does not happen any more. But that would suggest we were getting close to the limits with R22/R407C
I truly think this system averages 36-48 going down the road, Maybe a little lower at idle.
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What did you have running at the time, just the main evaporator? Because that TXV is 10 ton and if the dash and rack airs were on, based on the TXV used that is another 4-1/2 tons of evaporator.
Jim
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I dont have the Rack Units, So Main, and Drivers. I think the MO99 runs a little higher discharge pressure then the R22. My guess is the R22 was right at the high limit switch. So the MO99 pushed the discharge pressure over the limit. Again, only at really high RPM.
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Good info.
So what is the max RPM that the series 60 will normally run in a bus? (I don't have a tach)
Jim
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Lol, I dont have a tach ether, It's not very fast... 2100RPM according to wikipedia.
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Maybe Carrier has a performance curve for that compressor?
Jim
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I can not find one, there definitely would be, considering its variable speed.
Based on my reading TXVs can typically throttle down to 35% of their rated capacity. So that 10Ton TXV should be able to throttle down to 3.5 Tons. That might explain why its so large. So It can handle the full range of the compressors capacity.
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Makes sense. Then the dash and rack TXVs should be able to go down to 1/2ton each, if they are switched on. Sounds like the compressor is the limiting factor.
Jim