Powering Coach AC While Engine is Off

[Jim Blackwood]

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

[jap42]

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.

[brettpearson67]

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.

[Jim Blackwood]

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

[jap42]

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.

[chessie4905]

GM A-6 compressor is very versatile for build your own system.
https://www.hemmings.com/stories/article/frigidaire-a-6-air-conditioning-compressor

[jap42]

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 

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.

[Jim Blackwood]

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

[jap42]

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.

[Jim Blackwood]

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

[jap42]

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.

[chessie4905]

$795 just for the compressor? What is the vehicle you are putting this in?

[jap42]

Mci 102A3

Thats new retail. I would buy a reman or overstock.

[richard5933]

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.

[Jim Blackwood]

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