Factory Heat and A/C Systems

[PNWorBUST72]

I purchased a Maintenance Manual but I am not sure it will cover this generic stuff...

Can someone help explain the way the heat and A/C work in these MCI8's?


The metal "channels" on the bottom of each side is a heat duct to bring heat from the back to the front and windows? 

Whats the center channel used for?  Can I cover it with plywood and get rid of the "ramp" effect in the front?

Where is the defroster/driver heat coming from or delivered too?

[gumpy]

Large heat exchanger and two large squirrel cage fans in the compartment between first bay and fuel tank. A/C evaporator also there. Condensor in compartment behind left front wheel.

Two channels along the sides under the windows are air supply to the coach. The air comes up behind the wall panels and exits just below the windows.

Tunnel below the center isle is air return. Air is pulled in along the sides of the ramp and also through a few areas in the bottom of the supply channels on the sides.

Does the bus you are looking at have the OTR air conditioner still intact? That would be unusual. Most people remove it because it's very expensive to maintain. Some keep the heat, some don't.

[PNWorBUST72]

Yes, the parts are still there but I haven't confirmed the AC works or not.  The owner seems to be a bit evasive there so I am betting it doesnt.  I will check and work the price accordingly...are these repairs pricey?

I have seen alot people talk about killing the OTR heat but I am worried about losing the defroster.

[richard5933]

Yes, the parts are still there but I haven't confirmed the AC works or not.  The owner seems to be a bit evasive there so I am betting it doesnt.  I will check and work the price accordingly...are these repairs pricey?

I have seen alot people talk about killing the OTR heat but I am worried about losing the defroster.

If you still have the lines with coolant running to the front of the bus then the defroster shouldn't be hard to get/keep running, even if you have to add an aftermarket. It's nothing more than a small heater core with a ducted fan.

[gumpy]

Yes, the parts are still there but I haven't confirmed the AC works or not.  The owner seems to be a bit evasive there so I am betting it doesnt.  I will check and work the price accordingly...are these repairs pricey?

I have seen alot people talk about killing the OTR heat but I am worried about losing the defroster.

I converted my bus AC to R134a freon. Replacing the hoses, freon, dryer, and compressor oil cost me over $700. I've had to recharge it at least 4 times now. Had to replace the hoses twice at a cost of over $300. Takes 24 lbs of freon. R134a is now running about $100 per 30 lb canister.  Yeah, it's pricey to keep it running, but when it's hot out, there's nothing better than the bus air.  

BTW, that was doing it myself. If you have to have someone else do it, triple those numbers.

[buswarrior]

The same ones who advocate dumping the coach heat...

can't comfortably use the coach when there's a freeze, which happens everywhere in the lower 48...

Why give up free, prodigious heat whenever the coach is being driven?

Now, the coach AC is an expensive mistress to keep working on an old coach. Has to be watched over with a religion, parts changed out to make it gas tight, and operated regularly to keep it that way. Most busnuts don't run the coach often enough for it to stay well circulated.

The dash heat cannot be readily replicated. No matter your decisions about the coach HVAC, protect the coolant lines to and from the dash heat exchanger.

happy coaching!
buswarrior

[PNWorBUST72]

So lets assume the best...both the heat and ac works and I want to keep them.

If I remove the side channels, doesnt that kill the heat?  How do you keep the heat throughout the bus without keeping those returns?


Where are this lines to the front I am looking for, under the passenger side flooring, wrapped in insulation?

https://www.youtube.com/watch?v=mzkAJ4rQ24A&list=PL24A5AEC8B27BDD79&index=9 - Look around 8:55 for the pipes I am talking about.

I dont think the owner pulled the floor up so the pipes are probably still there, where they connect is another question.

Anyone have any pics of the AC parts and some general tips on telling if they are in good condition or is it simply, "Is the AC blowing cold?"


Thanks!

[gumpy]

So lets assume the best...both the heat and ac works and I want to keep them.

If I remove the side channels, doesnt that kill the heat?  How do you keep the heat throughout the bus without keeping those returns?


Where are this lines to the front I am looking for, under the passenger side flooring, wrapped in insulation?

https://www.youtube.com/watch?v=mzkAJ4rQ24A&list=PL24A5AEC8B27BDD79&index=9 - Look around 8:55 for the pipes I am talking about.

I dont think the owner pulled the floor up so the pipes are probably still there, where they connect is another question.

Anyone have any pics of the AC parts and some general tips on telling if they are in good condition or is it simply, "Is the AC blowing cold?"

Yes, those are the defrost lines. They split off the main heater lines which run through the lower part of the tunnel (below the wood floor in the air return tunnel shown in that video). They run across behind the driver's seat and up through the bottom of the side electrical panel access. The shutoff valve is on the left of the driver. Then they run over to the defroster compartment under the dash.

As for the AC, you can try it and see if the compressor clutch activates and it blows cold. If not, it's anybody's guess as to what the problem is. Could be freon leak, which means a cracked hose maybe. Could be mechanical.

[buswarrior]

Same as a forced air HVAC in a house, you need ducting to direct the air where you need it.

Some busnuts have modified and re-designed their duct work, but you need to be prepared to deal with the consequences of the lost distribution.

A full set of manuals has all the pictures and schematics.

As for the AC, if you aren't an AC tech, there's little we can do on here to teach you. Check and see if it blows cold, and that the compressor keeps engaged.

There are precious few busnuts with coach AC, it co$t$ and co$t$ and co$t$...

Happy coaching!
Buswarrior

[richard5933]

We have both the factory OTR a/c and heat. Both work well. It does cost money each year to maintain them.

The ducting down the two sides of our bus are partially used to carry the heat/air throughout the bus. For areas where the original vents were covered with built-ins, bathroom, etc. the converter just joined 3" or 4" ducting to it and carried the air to where it is needed. For example, there is a duct running from the floor duct up and over the kitchen cabinets - it exits above the microwave. Other places they went below and the duct exits in the toe kick area.

Just be sure that you have enough surface area for your intake/exhaust to allow for adequate flow.

We also have three electric space heaters built into the cabinetry and a small baseboard heater in the bathroom for use when on pole or gennie. There is also an LP furnace which runs on 12v for times we have no pole and don't want to run the gennie. Whoever designed out coach wanted to be certain they were warm.

[PNWorBUST72]

Current owner says the ac compressor /clutch engages but he can't tell if the air is cold or its just the weather, its been in the 50's here i the AM.  I am going to assume at VERY least its not working properly...

Are the 8 returns on the side of the bus for delivering heated/cooled air to the inside of the bus?  What are the ramp returns for and do people keep thoise just cover the floor with plywood?  Is there a reason why the front returns are actual sheet metal versus the back being like a fabric tubing?

[gumpy]

Current owner says the ac compressor /clutch engages but he can't tell if the air is cold or its just the weather, its been in the 50's here i the AM.  I am going to assume at VERY least its not working properly...

Are the 8 returns on the side of the bus for delivering heated/cooled air to the inside of the bus?  What are the ramp returns for and do people keep thoise just cover the floor with plywood?  Is there a reason why the front returns are actual sheet metal versus the back being like a fabric tubing?

If the clutch engages, then it has some freon in it.

The returns along the sides (two in front, two in back) are just that. Return air for the heat/A/C. They simply connect into the central return air tunnel.  There are two supply holes, also. They are the large holes which are basically above the battery compartment and are adjacent to the top of the ramp inside. Those are connected to the heater blowers. If you open the heater blower compartment in the front bay, you'll see the ductwork on either side of the blowers. This is the only place where the heater air comes into the coach. All the rest of the holes are the returns. I think one is for fresh air from outside. Driver's side front.

[PNWorBUST72]

If you still have the lines with coolant running to the front of the bus then the defroster shouldn't be hard to get/keep running, even if you have to add an aftermarket. It's nothing more than a small heater core with a ducted fan.

So for front defrosters its just like a car, heated coolant brought through a heater core and the fan blows air through it and up the defrosters?  Those are working...

I am thinking I will use as an aftermarket Planar diesel heater and just use the air return channel to run my ducts to the various zones...

[richard5933]

So for front defrosters its just like a car, heated coolant brought through a heater core and the fan blows air through it and up the defrosters?  Those are working...

I am thinking I will use as an aftermarket Planar diesel heater and just use the air return channel to run my ducts to the various zones...

Remember, the HVAC systems on a bus were HUGE coming from the factory. Hard to duplicate with other options.

If you are getting engine-heated coolant all the way to the front to run the defrosters then you won't need a diesel heater while on the road. It will never produce as much heat as your bus engine. Simply tap into the existing coolant lines and run toe-kick heaters under your cabinets. The diesel heater would be more for when you're not running the engine.

If you plan to use the diesel heater to keep warm while not running the engine but you're going to use the factory coolant lines for it, they you'll want some way to isolate the engine from the loop when it's not running, as it will act as a huge heat sink and suck all the heat out of the system while you're trying to heat the cabin.

[dj]

Hey if anyone has the ducts that run the length of the bus long the walls that they have removed Im am interested in them    I have a 1988 MCI 102A3 leave a note here I check it pretty often   Thanks