Poor A/C performance at low RPM

Darth

Registered User
I have a 92SC that was originally set up for R12. I have since converted it to R134 simply be changing the charging connectors and adding the 134 (no comments please). All worked well except over the winter, I would lose some charge that required more refrigerant. This year, I decided to convert to a hydrocarbon refrigerant due to larger molecules and increased efficiency.

I have since had trouble with cooling at low RPM. The directions stated to charge at 40psi low side at idle. Since I couldn't get proper cooling at idle, I decided to charge at 2000RPM and see what happened. I got about 30psi low side and 250psi high side. This still gave me very poor cooling in town. At highway speeds, it will freeze you out of the car. The refrigerant supplier insisted that I start over again (releasing all the refrigerant) and charge to 40psi low side at idle. This gave me only 150psi high side and 70degree vent temperature with 85degree ambiant. The car still cools pretty good at highway speed.

My local a/c guy says either my compressor is going or the orifice is stopped up. Without getting into the hydrocarbon refrigerant debate (It is being used in Europe), what is the consensus of opinion here? Do I need to pop for a new compressor?
 
What is the high side reading at 2000rpm? This will tell me wether it is a compressor or condenser/orifice problem...What is the temp coming out of the vents at idle? And on the highway?
 
a/c

Sounds like you know quite a bit about a/c systems, so if I'm all wet please ignore me. If you just changed the fittings and added, coolant, (etal) did you pump the system down with a vacuum pump properly? If not the differential between the hi and lo sides may be lacking. To a point, the more diifferential, the better the system works.
 
Sounds like you know quite a bit about a/c systems, so if I'm all wet please ignore me. If you just changed the fittings and added, coolant, (etal) did you pump the system down with a vacuum pump properly? If not the differential between the hi and lo sides may be lacking. To a point, the more diifferential, the better the system works.

With the R134, I did not. Since I went to the hydrocarbon refrigerant, I bought a a/c vacuum pump and did it right. Held vacuum for 1 hour.
 
Temperatures from the vents? Along with ambient outside temperature?

Outside ambient = 88F

2000 RPM
25psi low side 180psi high side
78f vent temperature

Idle
35psi low side 135psi high side
86f vent temperature

Highway speed (60mph)
52f vent temp

I tried to measure temp on both sides of the orifice using a lazer gun and got 153f on the compressor outlet side and 132f on the other side.

Hope this helps.

Ted
 
radiator fan. that would explain you not cooling sitting at a stoplight.
because with air moving over it, your ac seems to be functioning correctly.

if you want a boost in cooling, a pusher fan, wired through a relay triggered by the pressure switch is a great addition.
 
radiator fan. that would explain you not cooling sitting at a stoplight.
because with air moving over it, your ac seems to be functioning correctly.

I don't think 52 degrees F at the vent at highway speeds is functioning correctly.
 
I don't think 52 degrees F at the vent at highway speeds is functioning correctly.

Either your refrigerant charge is insufficient or your compressor is weak. Both pressures are too low at idle and 2k rpm. I would say it is a refrigerant problem. What type of freon are you using exactly? 52 degrees at the vents is 8-10 too high minimum. Especially at 2000rpm. A fan problem would be indicated by a huge high side reading (over 350psi). As would a restriction in the orifice or condenser. Either your charge is not enough or your freon is not efficient enough...
 
You can try a fine spray from a garden hose to your condensor while doing the run-in test to see if that helps, if it does then your condensor has air flow problems. Is your engine temps good while the AC is on? I run ES-12a , Have for years.
 
Either your refrigerant charge is insufficient or your compressor is weak. Both pressures are too low at idle and 2k rpm. I would say it is a refrigerant problem. What type of freon are you using exactly? 52 degrees at the vents is 8-10 too high minimum. Especially at 2000rpm. A fan problem would be indicated by a huge high side reading (over 350psi). As would a restriction in the orifice or condenser. Either your charge is not enough or your freon is not efficient enough...

I am using ES12a from Autorefrigerants.com . I was getting better results when I charged at 2000 RPM instead of idle. I think that I will add some more, but never did get good results around town.

I am afraid my compressor is going away, but I hate to shotgun.
 
Oh.. nevermind.. just saw you're using barbeque gas.. Unfortunately I can't help you out on that. :rolleyes:
Really, some people use propane and it works.. But you're entirely on your own with it.

And also wrt the fine print/faq on that company's website. They quoted a part of some EPA statement about replacements for r134a that has nothing to do with actual law. An EPA statement about general usea does not make the use of a HC refrigerant legal. That's governed by state law and, as far as I know, no US state allows it. Interesting how they omit that part. Its a shady operation. I'm not sure its even legal to ship it.

If you ever sell the car, you might want to disclose the fact, or just purge the contents, so you don't open yourself up to some sort of lawsuit in the .01% chance something were to happen. :rolleyes:


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