ac compressor

[johnboy2]

This may be the wrong place to ask.
I have a sport coach with a spartan chassis and an 8.3 cummins non electronic motor

I need to replace the ac compressor with one that uses 134a the old r12 unit seized, and yes I know I need to change the expansion valve as well and clean the lines.

So if anyone outhere with a bit newer rig could look at there compressor and reply with make mod ect,

thanks
john

and again if I'm in the wrong place, sorry .

[RinkersRanch]

All new/rebuilt a/c compressores have seals compatable with R134a and PAG or Ester oil. PAG oil is used in OEM installed systems, Ester oil is used in a retrofit. Just find a compressor that will replace your old one and you are good to go. Has the system been previously changed to R134a or are you doing the retrofit / recharge yourself? If you are doing it yourself I would be glad to give you some pointers. I use to teach a class on 'R12 to R134a retrofitting' for a Caterpillar dealer and I would be glad to help if you need it.

[johnboy2]

I Found a company in az ( Arizona mobile air ) that has the compressor and seem to be willing to work with me on the other parts.

Wayne I would like any help you can give me on the conversion. My son is well trained on ac systems but has no experince on mobile systems, so we know how and all the tools to do the job but dont know what parts need to be changed out and don't know how much charge to put in.

this is what I know

someone charged with 134 as it has a 134 low side fitting
the compressor is siezed
the sys is holding about 75 psi for 3 years

thanks for any help

john

[TXiceman]

Be sure and flush out all of the old oil and refrigerant. You can get some problems mixing the old oil and the new oil....foaming and polymerization.

Ken

[chadandapril]

I replaced my compressor not long ago I got the new one from www.techchoiceparts.com Mine used a Seltec TM15 but the tech guy said it was probably originaly a sanden compressor both are real common on big trucks and equipment Be sure to get the same size pulley as your old one

[RinkersRanch]

Ok John, you got to be careful what you ask for. Just kidding. This is a Very short version of a 2 day R12 to R134a course I use to teach to mobile A/C mechanics. Forgive me if I have left out too many details. Please ask me to clarify anything that is confusing.

Sounds like you are familiar with A/C service and required tooling. It also sounds like someone did a ‘quick retrofit’ to R134a.
A couple of notes. R134a and the mineral oil used in R12 system is not compatible. If mineral mixes with R134a it forms a black tar like sludge that will plug an Expansion valve or an 'O' tube or might ruin a compressor. Ester oil used in a retrofit will mix with R134a and mineral and will significantly reduce or eliminate the sludge problem. That is the reason for using Ester oil instead of PAG. Ester will also mix with PAG oil. There are a couple of different PAG oils which should not be mixed, so if you are not sure what oil is in the system use Ester oil. R134a is a smaller molecule than R12 and will leak where R12 will not. R12 hoses that have run for at least 100 hrs on a working R12 sytem and have no leaks or cracks will hold R134a quite well.

This is what I use to teach my students in my R12/R134a retro-fit class.
The part that MUST be changed is the receiver dryer. The desiccant in an R12 Dryer will be dissolved by R134a and can plug up a system or kill a compressor.
A new compressor is also a real benefit. This is a disputed step but I recommend always changing the oil in the new compressor. Compressors are usually filled PAG oil and stored. This oil has most likely absorbed some moistrue and should be changed. Also Ester oil is needed for a retrofitted system, no matter how long since it was redone. Use NEW Ester oil from a sealed container. Ester oil absorbs moisture at a tremendous rate. Ester oil is clear as water when new. NEVER use Ester oil that is even slightly amber. Just pour out the old oil into a measured container. Add the same amount of Ester oil as was removed.
An R12 ‘E’ valve will work but an R134a ‘E’ valve has better operating characteristics for an R134a system. You will need a set of R124a retrofit connectors to put on the R12 fittings. (high 13mm and low side 16mm) You will also need an R134a manifold gauge set. If your system has no leaks, even a minor oil seepage will leak R134a. The R12 hoses and seals that are not leaking or cracked will hold R134a without leaking.
Flush with a compatible flush until the flushing fluid comes out almost clear.
Close up the system and use the best vacuum pump you can find. (at least 2CFM but the more CFM the better) Pull a good vacuum (30min or so) close off the pump, and see if it holds a vacuum. If the vacuum increases more than 5”Hg in 10 minutes you have a leak. Fill with R134a gas only and using a leak detector to find the leak. If vacuum increases only 2-4"hg in 10 minutes it is most likely some trapped refrigerant seeping out. Refrigerant will get trapped in and around seals and using a long hard vacuum will pull it out. Use the vacuum pump another 30 min. System must hold a 29.5"Hg vacuum for 30 min before you can be sure it will hold and not leak R134a. Once the system will hold this vacuum, open the system and fill with Add about 5 ounces of Ester oil to replace the oil flushed out.
Close the system, connect and run the vacuum pump for at least 2 hours after 29.5”Hg is reached. The longer you use the vacuum pump the better your final result will be.
Determine the original R12 charge. Calculate 80% of the specified R12 fill capacity. R12 systems can stand a little over charge. R134a systems cannot. DO NOT OVERCHARGE. R134a must be added by weight. Gauges cannot be used to determine the correct charge with R134a as it could with R12. Once an R134a system reaches 'ovecharge' the gauges do not change as they do with R12. I have put 2X the the proper charge in my training system and the gauges reach a point and do not change. BUT the vent temp steadly drops as the system goes into an overcharge. I tell and show my guys 'R134a acts wierd'. So A slightly low charge cools better than a slight overcharge. Fill the system with 6 oz. less than the 80% charge. Close off the manifold gauge valves.
Start and run the engine a little above idle. Between 1000rpm and 1100rpm (steady rpm is more important that the exact rpm) Turn the A/C system on high while closely monitoring the temperature on the vent with the strongest air flow. Use an additional fan to help cool the condenser. Allow the system to stabilize for about 5 min.
Add the remaining R134a, very slowly, as a gas into the low side while monitoring the vent temperature. Add a little refrigerant stop and monitor the vent temperature for about 5 min. Continue to add a little refrigerant and check the vent temperature. When the vent temperature increases ANY even 1 degree F. STOP adding refrigerant. You are done. Take a test drive. Turn the system on high and check the vent with the highest air flow. At a highway speed of between 45 - 55 mph, R134a can acheive about a 25 - 30 degree F drop from ambient.

[johnboy2]

Thanks wayne and all who have helped with that last info i'm almost ready to start the only flag still up is to try to come up with what the r12 charge was.
wayne what about the oil charge and the 65 feet of hose from the compressor to the evap and cond ?

again thanks all I love this forum
john

[RinkersRanch]

WOW, what, the Evap. and Cond. in the next county.
Sorry, had to give you a little hard time.
In answer to your question.
About one oz. for every 10 feet of the low pressure line only. The hot line hardly holds any oil at all. Is the entire 65 or so feet all rubber hose? That is a lot of hose for R134a. That stuff will leak right through the wall of a rubber hose. The new hoses are lined with Nylon and this helps but, old R12 hose still in good shape will loose about 1-2 oz per 10 foot of the high pressure line about every 500 hours of use. Give or take a little depending on the quality of hose. This seapage only happens, on the high pressure line, when the high side hose is at 125psi or higher. So when the system is off, leakage through the hose wall is less that .1oz /year. I would not be suprised to see a loss of 3-4 ounce per year. Not a real big problem, but one you want to be aware of. You will probably need to top off the system every year. Use the same procedure as adding the final 6 oz to top off. Told you this R134a stuff is wierd.
There is a way to fill without knowing the capacity but it is real tricky. If you and or your son are VERY framillar with using the refrigerant gauges (must be R134a manifold set, not a converted R12) {you need the Temp/press relationship for R134a} and know how to charge liquid. I can give you some pointers that I have had success with. I'll do some digging in my class notes and see what i can come up with.
BUT . . .
Don't let anybody try to tell you that R134a will not cool. It is just so much more touchy that R12. A long hard vacuum is one of the keys to getting good results. If your son has refrigeration experience he knows the need for such a long hard vacuum procedure. Moisture and air are not tolerated with R134a as they were with R12. Sorry for getting so long winded again.

[johnboy2]

Thanks again Wayne
Yes I'm sure trere are maney times the the evap and cond reach new countys even states before the compressor. That may be the reason the don't get along together well.

[johnboy2]

Well I have the dash air working thanks to the help I got on this post and my Son Who has far ahead of me on ac systems.

Here is what we did
1 New compressor , reciever dryer , all new O rings ,ester oil

2 used compressed air than nitrogen to blow out all the hoses and componets that wern,t replaced

3added 4and a half ozs of oil

4 reconnected all the parts pressure tested the sys with 100 lps of N2 for 1 hr

5 filled and dumped with N2 3 times at abt 30 min. intervils to remove air and moisture

6 evacuated sys overnite (800 microns with the pump on abt 1500 pump off

7 charged the system with 2lbs 3 oz of 134 (used the charge size from my saturn as a starting point as we had no clue what charge was before) then added very slowly til we got a 20 deg dif at the discharge in the bus. final charge 2 lbs 10 oz

8 here are a few facts at 500 rpm engin speed
back pressure 32 lb
discharge pres 190 lb
suction temp 53 deg
sup heat 15 deg
liquid temp at the reciever 123 deg
liguid at the sight glass with ocasional bubble

[RinkersRanch]

Coolness is a wonderful thing. Sounds like you did an excellent job. That is probably the cleanest, dryest R134a system on the planet. I was just hoping to get you to keep the vacuum pump on for more than just a few min. Wow what an excellent job cleaning and drying a system!! Clean and dry is what R134a likes so you should have a great working system for a long time to come. Your boy really knows what he is doing with this refrigerant stuff. Your final numbers are exactly what you are looking for.