Over The Road Air Conditioning

[Jim Blackwood]

Well, the DL has a 10 ton main evaporator, and 3ea 1-1/2 ton smaller evaporators, one behind the dash and two in the overhead bins. I'm not sure the system fully supports all of those since I seem to remember it being rated at 13 tons overall but they add up to 14-1/2 tons which is 174,000 btu. Even 13,000 tons is 156,000 btu. So somewhere between those two.

That's a lot of cooling. Even six roof units wouldn't really come close.

You can't get that from a shore-line. No how, no way. To get it from a genset would probably take a 40kw unit so that's not practical either. So the real question is, how much can you get?

New Homeowner's A/C units have been showing up with variable output compressors unless I'm mistaken. I do know efficiencies have risen to seer 22 or better, whereas the efficiency of the DL OTR might very well be under 12. So a modern compressor about half the size should give acceptable results.

How large of a compressor can you drive on a 50 amp shore line? Or a 30 amp line? That's the limiting factor.

Jim

[buswarrior]

Stock HVAC has a heavy fresh air component, and has to potentially cool 55 passengers.

Roof airs are closed loop, only wind driven air infiltration, and a handful of bodies.

Can't remember the BTU heating of each human body, it adds up...

Apples and Oranges, pick your fruit.

Happy coaching!
Buswarrior

[Jim Blackwood]

Anyone want to hazard a guess as to what the pressures would be when you put enough r134 in the DL to fill the lower sight gage on the accumulator? I know on mine it would have to be over 50/225.

2nd question, is the compressor crankcase pressurized or not?
What is the correct procedure to add compressor oil?
What oil is specified?

Finally, has anyone had an issue with closing the condenser/door where it drags on the bottom and how did you fix it?

Jim

[buswarrior]

Condenser doors all drag, used to be a skid plate it rode on into place on some models. Nothing to fix. Lots of weight hanging there, don't be careless in leaving it hanging open except when directly working on it, you can see the mess a hinge or attachment failure will be to remediate...

Long ago, and I had knowledgeable help... we did the R12 to 134 swap, changed the oil from old kind to new compatible kind, it came in gallon cans, it drained and filled via plugs. There's a name for each of them, and they shouldn't be mixed up.

Yes, compressor is a sealed unit, that's why the shaft seal is a devil.

Gauges were the other guy's specialty, and he was more interested in the gauge readings than the sight glass.

Happy coaching!
Buswarrior

[muldoonman]

You boys Compressor look like this one?? Carrier O5G-Bus 41CFM

[buswarrior]

Nothing like a fresh compressor!

Happy coaching!
Buswarrior

[richard5933]

That thing is huge compared to the little rotary compressor in my GM. Hard to believe that ours stays cool after seeing that monster.

[muldoonman]

Think it's a 6 cylinder monster. Bought this one from Carrier last fall and found out  mine just needed a seal behind pulley.  Now I have a 150 pound spare. Might have to bequeath it you somebody that needs a redo.

[richard5933]

For comparison, here's the one on our GM 4108. It's not much different than what you'd find on a 60s or 70s Chevy or Olds.

[Jim Blackwood]

Yeah, it's a beast.

So if the crankcase level is a bit low how do you add oil? (It just comes up to the bottom of the sight glass.)

I couldn't help noticing that there are valves on the lines so the pump can be isolated. So if you shut those off, open the crankcase and add oil, can you then evacuate the pump using the fill fittings on the compressor that you normally use to charge the system? It seems to me this would be the way but I thought I should ask.

As for the condenser door, it has sagged so badly that even with the skid plate it won't shut completely. In fact it hits the outside edge of that skid plate and stops. And if the fans are running when I try to close it it pushes the screen over into one of the fans. Not good. Not good at all.

Jim

[muldoonman]

For comparison, here's the one on our GM 4108. It's not much different than what you'd find on a 60s or 70s Chevy or Olds.

Just curious, Does that ac/compressor set up keep your bus cool in extreme heat. Just got back from the Gulf Coast last week (Galveston) and in 103 degree heat, mine (Prevost stuff) would freeze you to death.

[richard5933]

Just curious, Does that ac/compressor set up keep your bus cool in extreme heat. Just got back from the Gulf Coast last week (Galveston) and in 103 degree heat, mine (Prevost stuff) would freeze you to death.

My bus was originally purchased for operation in NJ and surrounding states. I've used it in the summer between NJ and Gillette WY. So far we've driven in outside temps pushing the upper 90s, and the interior stays about 73 degrees. The driver's area is slightly warmer since it's in front of the air intake on the floor, but if the driver's fan is running it circulates the air and keeps things comfortable. With outside temps in the 80s the bus will be a meat locker if I want.

For operation in southern states and hotter climates, GMC offered an option to have two of the compressors mounted side-by-side to double the capacity of the system. The shared a common manifold on the rear so that they both tied into the refrigerant plumbing.

On the double-compressor setup I don't know if both were always running, but I suspect so. On mine the compressor can only be turned on with the oil pressure below a certain setpoint, and I would guess the same is true on the double setup.

I'm sure that if mine can keep things comfy in the 90s, the double compressor setup could easily cope with warmer temps.

[Jim Blackwood]

Is this double compressor supposed to help me to know how to add oil somehow?

Jim

[richard5933]

Is this double compressor supposed to help me to know how to add oil somehow?

Jim

Not really. I was just answering the question asked about it.

Doesn't the manual for the bus indicate how much oil is supposed to be in the compressor?

[chessie4905]

I would think his manuals, if he has them, would indicate this info.