Over the road AC

garhawk · April 20, 2014, 04:34:50 AM

What is the procedure for identifying the coolant in an over-the-road air conditioning system? (R22, 134, etc.)

Are there any two that can be mixed?

muldoonman · April 20, 2014, 05:12:57 AM

Thanks a good question Gary and I'm sure one of these smart guys will answer. As for me, I have Freeze 12 freon that's compatible with the old 12 in my 91 8V92TA Prevost as I haven't converted it over to 134 as of yet. It's been holding a charge for years and I just have the same Tech check it every year and he knows the drill,. When I have to make a change he will do it and change oil and whatever else at that time. Bought my Freeze 12 at Napa but called the other day and they said they quit handling it. It would freeze you to death inside. R22 in my Cruiseairs underneath.

luvrbus · April 20, 2014, 05:51:32 AM

Gary, the best way if you can see it and I assume you are talking about the Carrier in rear of your 20 is find the tag but I have seen nothing but R134A in the NJT model 20's fwiw

good luck

digesterman · April 20, 2014, 11:07:05 AM

I am pretty sure the service valves are different, but you would have to have someone familiar with which was which. Years ago we had some semi's changed over to 134 and they told me at that time that was one of the differences.

oldmansax · April 20, 2014, 04:32:34 PM

Gary,

You can tell by comparing the pressure to a pressure-temperature chart. Here is the procedure:

The bus needs to be at rest, not having been started for at least a day. What you are looking for is the entire AC system to be the same temperature throughout, meaning the inside, outside, compressor, and evaporator. Take the temperature using a KNOWN GOOD ACCURATE THERMOMETER. I usually tape or wire tie my temp lead from my Fluke multimeter to one of the service valves & leave it for about 5 minutes for it to stabilize. Connect a KNOWN GOOD ACCURATE AC gauge set to the system. You only need to connect the red high (discharge) side gauge. Make a note of the temperature and pressure and compare it to a PT chart. You can find them on the internet or buy them at any good HVAC supply house. Here is a link to one:

http://www.chillers.com/PT%20charts%20for%20refrigerants.htm

For example, if your temperature is 70F & the pressure is 121#, you have R-22. If the pressure is 70# you have R-12, 71# is R-134A. Not much difference in 134A & 12 but the higher the temp, the more difference. Also, 12 would not have been used unless the system is REAL old.

There are other ways but this one is the simplest.

Also, if the system is still using the correct charge is was designed for, the access valves will be different. R-12 & R-22 will be screw on access, R-134A will have the push on connections similar to an air hose. The problem there will be somebody may have changed a 12 system to a 134 system & not installed the access adapters.

TOM

Nick Badame Refrig/ACC · April 21, 2014, 03:04:18 AM

Hi Gary,

To add to Tom's post, you can also identify the refrigerant by finding the expansion valve in the

evaporator compartment. It will be labeled which refrigerant it's made for.

Nick-

oldmansax · April 21, 2014, 04:59:01 AM

Hi Nick,

I thought about adding that but the labels were gone on almost all of the old systems I've worked on.

OR, they were on the back side where you couldn't see them!!

TOM

luvrbus · April 21, 2014, 05:19:31 AM

Here this should help straight from a NJT model 20 manual 21.8 lbs of R134A

Nick Badame Refrig/ACC · April 21, 2014, 04:26:53 PM

Quote from: oldmansax on April 21, 2014, 04:59:01 AM
Hi Nick,

I thought about adding that but the labels were gone on almost all of the old systems I've worked on.

OR, they were on the back side where you couldn't see them!!

TOM

Very true Tom!

Nick Badame Refrig/ACC · April 21, 2014, 04:31:14 PM

I just did a 05G external rebuild on a 2000 Prevost XLII today.

Pretty simple as long as you are sent the right parts... Hint, Hint, (prevost)

Hub piloted bearing, seal, pulley, clutch, poe oil change and recharge.

https://www.facebook.com/media/set/?set=a.730834860270007.1073741857.340297602657070&type=1

Nick-

garhawk · April 27, 2014, 05:15:29 AM

Thanks for all the help folks.

Turned out my Eagle model 20 has a Thermo King system with R22.

Mixing valve was stuck partially open and allowing heat into system. Disconnected mixing valve for time being and pumped in 16 lb of R22.

We now have cold air to head down to Wayne's Louisiana crawfish gig.

Oonrahnjay · April 27, 2014, 05:52:38 AM

Quote from: garhawk on April 27, 2014, 05:15:29 AMThanks for all the help folks.

Turned out my Eagle model 20 has a Thermo King system with R22.

Mixing valve was stuck partially open and allowing heat into system. Disconnected mixing valve for time being and pumped in 16 lb of R22.

We now have cold air to head down to Wayne's Louisiana crawfish gig.

Are we talking about "the Same Valve" here, Gary?

garhawk · April 29, 2014, 06:03:25 AM

Hey Bruce,

Yep. Me thinks the root problem may be in the temperature control (potentiometer).

Come on down. Need help!

Gary

Oonrahnjay · April 29, 2014, 09:24:41 AM

Quote from: garhawk on April 29, 2014, 06:03:25 AM
Hey Bruce,

Yep. Me thinks the root problem may be in the temperature control (potentiometer).

Come on down. Need help!

Gary

Yeah, I didn't trust either the solenoid (although that's simpler) or that potentiometer control when we were working on it. What's involved in changing the temp control out?