I've recently rebuilt the air conditioning system in my stock 1985 Fiero with the 2.5L. Flushed lines and coils, installed new compressor, compressor clutch plug w/ diode, both switches on the back of the compressor with new 2 wire plugs for those, new accumulator with new clutch switch set for 134A, and new variable orifice. I drained as much oil out of the new compressor as possible and replace with Ester oil with dye. I added 6.5oz of oil into the system to get the entire system up to 8oz of oil. I pressure tested the system at 110psi with nitrogen. It held perfectly for 18 hours. I then pulled a vacuum on the system for an hour before I started filling with 134A refrigerant. I put in 33oz to start. Then ran the system for a while to get everything distributed. So here is my current issue...
At idle the cooling system seems to work great. But any time the engine RPMs get above 2,000 the clutch short cycles like crazy as the low side pressure is dropping to below 20psi. So here are the numbers I was able to get with it the other day.... 75 degrees F outside Fan set to Hi, A/C set to norm. Engine idling for at least 10 minutes... High side pressure: 232psi Low Side pressure: 33psi 42 degree F air out vents After 20 minutes idling... High side: 285psi Low Side: 28psi
Switch to MAX on the A/C control. Fan still set to Hi.. High side: 257psi Low Side: 23psi 32-33 Degree F air out of vents Icing slowly starting to build on the accumulator and the line after. Set the A/C back to Norm from Max and the icing goes away.
In both scenarios the compressor clutch doesn't actually ever cycle off.
Now, if I just hold the gas pedal down to hold RPMs at 2500, or if I'm cruising down the road at highway speed, the low side pressure drops below 20psi. The Clutch kicks off, the pressure raises, clutch back on. This happens every 3 seconds continuously when the AC is set to norm, and every 1 second if the AC is set to Max. I thought maybe the charge was too low, but I added a couple oz bit by bit and the system kept doing this. I even went all the way up to 39.25oz of total refrigerant in the system and the symptoms are the same. I know the system calls for 40oz of R12, and with R134A should only take about 34oz. So, my next theory, is there an issue with the variable orifice that I bought? Could it possible have plugged up some? Or maybe it's allowing too much through? I'm a bit stumped so any advice would be greatly appreciated! For clarification, here is a list of the parts I installed....
Isn't 232 psi getting high? (I don't know the standard high-side pressure in an orifice tube system.)
My first guess is water freezing in the orifice tube.
If you still have the little muffler on the compressor line, it may be the place where water could collect and take a long time to evaporate out under vacuum.
When you flushed your ac system was the condenser in the car? There are several low points on the ac lines that without sufficient velocity is hard to get all the old oil out.
Likely you're orifice tube has some debris-black gunk on it. I'm assuming the rad/ac condenser fan was on in both scenarios?
Yes, the condenser fan was running constantly in both scenarios. Sorry, I should have stated that. Also, while i did remove the evaporator coil to clean and flush it out, you are right, I left the condenser coil in the car when I flushed it. I ordered a new oem style orifice instead of the variable one, and another accumulator(simply because they are inexpensive) and will be changing those out later in the week. Hopefully you are right and I simply didn't get the condenser flushed out as well as I should have. Thank you so much you guys for giving me your opinions! I'll update this post with what I find once I get the parts and change things out.
I strongly suggest that once you get the system reassembled, you pull a vacuum for an extended period -- perhaps overnight or longer -- to ensure you've removed any water from of the system.
Thank you for the advice. I'll make sure to let it pull a vacuum for an extra extended period of time. Not a bad idea at all. Thank you again! ] I just got the parts so I'm hoping to have time to get to it in the next couple days while it's still warm out here.
[This message has been edited by budsutten1 (edited 10-02-2025).]
Well Stingray92, you nailed it. I must not have gotten everything flushed out of the condenser coil. As you can see in the picture, it's definitely plugged! I put a new standard orifice in it and replaced the accumulator again. I tested pressure with nitrogen at 120psi for 20 minutes and now I'm pulling a vacuum on it again, and per Brian's advice, I'm going to let the vacuum pump run for far longer than an hour this time. Thank you so much for all the help and I'll let ya'll know how this turns out. Hopefully all the gunk got flushed through and trapped at the orifice and it won't plug this new orifice this time.
Yeah flushing the system with components installed can be difficult. Something I've done is use a white cloth/sock to catch anything after I do the 1st flush.
It might be overkill but contamination is what will kill the system. I also had the luxury of having all the pipes and components out of my car for flushing before I did a final flush.
