P8M4108a OTR a/c question

richard5933 · May 28, 2018, 02:38:06 PM

The OTR a/c on our 4108 seems to be acting up. On the way out on our trip this weekend it took a while for the unit to start cooling where it was noticeable. Same thing happened a few weeks ago. Eventually it did okay and we were moderately comfortable inside the bus.

Coming home today with ambient temps hovering around 90 and with full midday sun, the temp inside the bus didn't get below 80 degrees. The compressor is running, the evaporator fan is running, and things look like they should. Problem is that the air is just not that cold.

My gut tells me that we've leaked somewhere and the refrigerant needs to be charged.

Any advice where to start the process? We have a 3-day drive to Wyoming in July, and having the OTR working by then will be a necessity to maintain domestic tranquility.

chessie4905 · May 28, 2018, 03:21:54 PM

Buy refrigerant in 30 lb container and learn how to charge it. You'll be dealing with this as long as you have onboard air in an older coach. The newer models started using double or triple seals of more resistant materials. I would imagine getting a recharge done at a coach service place is going to be $250 or more. Btw, Luke does this if you are near NJ. Maybe a truck service plaza will do it also. Do you have the dual compressors?

eagle19952 · May 28, 2018, 03:50:13 PM

Quote from: chessie4905 on May 28, 2018, 03:21:54 PM
Buy refrigerant in 30 lb container and learn how to charge it. You'll be dealing with this as long as you have onboard air in an older coach. The newer models started using double or triple seals of more resistant materials. I would imagine getting a recharge done at a coach service place is going to be $250 or more. Btw, Luke does this if you are near NJ. Maybe a truck service plaza will do it also. Do you have the dual compressors?

Neighbor just paid over $300.00 to fill a leaky 3T central air unit. 134a.
well the Home house protection plan did...

richard5933 · May 28, 2018, 04:01:58 PM

That was my gut thought... Low refrigerant. I thought that the tell-tale would come on and the compressor would shut down if that was the case though, which is why I was unsure. Maybe that's only if it's totally out.

We have the single compressor.

Anyone know which refrigerant this takes? I'm guessing whatever is most expensive. Can it be converted to the latest?

richard5933 · May 28, 2018, 04:43:20 PM

I just went through the receipts the PO gave me when I picked up the bus. He had it at Luke's for service.

Luke checked the OTR system and found no refrigerant. Ran a leak check and found no leaks. Refilled with 18 lbs of 134a. Cost was $504 for refrigerant, plus labor.

If he found no leaks, where did it go? Do leaks show up over the winter when things contract?

luvrbus · May 28, 2018, 04:56:58 PM

18 lbs of Freon went some where it has a leak.I have no idea how the HVCA works on a GM.one thing I do before I bring out the pump,gauges and Freon is check to be sure all the heat control valves are working proper,the AC loses the battle when in combat with the heater.I service a VanHool that is terrible about it and never needs Freon always a heat control valve

chessie4905 · May 28, 2018, 04:58:50 PM

Biggest leak will be at compressor seal. They leak more if not in use for awhile. After filling, you can use some ref. leak liquid and check all the joints yourself. This is why most pull the onboard air when they convert them. Bus companies used to buy the freon in big oxygen style tanks. Learn how to add it and buy a 30 lb tank.

luvrbus · May 28, 2018, 05:06:04 PM

I bought a 30 # at Sam's Club 2 weeks ago for $118.99 in fact I bought 2

richard5933 · May 29, 2018, 02:31:00 PM

Correction to my previous post...

Apparently when Luke had the bus last summer they put in 18 pounds of R22, which is why it was so expensive. The bus definitely takes R22 and Luke confirmed that the price on the invoice was for R22. His suggestion was to take it in to have another leak test performed and then repair/recharge as needed.

I'd love to do this myself, but at the moment I don't have the necessary tools/skills to pull it off. Took the bus to a local shop that works on heavy road equipment and buses. They repaired the a/c on our 4106 in the past and seem to think that they can get this going as well. I hope so - guess we'll see.

BTW, I did a test this morning to verify that the problem was with the refrigerant and not that the water modulating valve was sending through hot coolant and creating a problem. I started the bus from a cold start and immediately engaged the a/c. The ambient temp was 82 degrees. The a/c was blowing 78 degrees. After the engine was fully warmed up the a/c was still blowing 78 degrees. Then I opened the cover over the heater core & evaporator coil in the HVAC bay and confirmed that the heater core was still cold to the touch. Unless I've missed something, this all points towards a problem with the a/c system itself, probably a low refrigerant level.

Anyone know what would trigger the a/c stop tell-tale on the 4108? On the 4106 it came on when the refrigerant was low. Either that's not the case here or the refrigerant isn't low enough yet to turn on the tell-tale. Or maybe the tell-tale system isn't working.

luvrbus · May 29, 2018, 03:25:45 PM

R22 is expensive I would check to see how much to convert over to 134A I did it on a Eagle I own and wasn't that bad something like 800 bucks ,then everything is expensive on a GM

chessie4905 · May 30, 2018, 04:01:25 AM

Richard, if you check the sight glass on your liquid receiver tank after system is operating 30 minutes or more under maximum heat load, the liquid level should be in middle of sight glass.
According to the shop manual, 4108's didn't have the under dash evaporator or expansion valve. Maybe it was available as an option?

richard5933 · May 30, 2018, 04:09:15 AM

Quote from: chessie4905 on May 30, 2018, 04:01:25 AM
Richard, if you check the sight glass on your liquid receiver tank after system is operating 30 minutes or more under maximum heat load, the liquid level should be in middle of sight glass.
According to the shop manual, 4108's didn't have the under dash evaporator or expansion valve. Maybe it was available as an option?

My knowledge of a/c systems is minimal. I think I understand what the under dash evaporator would do (help cool the front of the bus) but I'm not sure what the expansion valve would do? And would either make a difference if the level of refrigerant is low?

chessie4905 · May 30, 2018, 04:17:05 AM

The expansion valve regulates the flow of refrigerant through the evaporator coil. If yours has this core, it sit on top of heater core and is aluminum colored. About two inches thick. The expansion valve is of medium size and all brass. Can be seen in upper lh corner in compartment by entrance steps.

FYI....https://www.refrigerationschool.com/blog/how-to/r22-replacement-what-hvac-techs-need-to-know/

RJ · May 30, 2018, 11:10:36 AM

Richard -

I'm not sure, but I don't believe the 4108s had a "dash air" unit like the 4905s did.

I, too, think that your system is low on "freon", but not to the point it triggers the tell-tale.

FWIW & HTH. . .

daddysgirl · May 30, 2018, 01:54:02 PM

I think your freon is low as well. We switched over to 134A long ago. I have several cases of refrigerant and the discharge/recharge valves. It's much cheaper than R22.
I would be curious to know if you've checked the sight glass? I don't know about your insulation, but if the system managed 10 degrees, I would bet your seals are leaking.
I also don't know if you have Drivers AC/Heat, but if so, have you tried just the drivers AC? I usually average a small can every three years, and my first test is the drivers ac compared to the coach ac.