Automotive Air Conditioning Information Forum

Hi all,

Restoring a 1994 GMC K1500 with 5.7 V/8. I installed virtually ALL new A/C system components, except the evaporator. I thoroughly flushed the evaporator, and pressure tested it for leaks. (None)

Vacuumed the system down for one hour plus, and then the system held the vacuum overnight with vacuum pump disconnected. I then started to charge the system as normal. Often times, if I work quickly, I can get enough freon into the system just from the vacuum, that the compressor will kick in and I don't need to bypass the pressure switch. In this case however, there was an electrical problem and the compressor didn't turn on. The system took a little under two cans on it's own, (about 20 ounces +/-) without the compressor running. Capacity is 32 oz. System calls for 8 oz total oil. New compressor came with 7 oz so I added 1 oz to new accumulator.

When I finished fussing with the electrical problem and got back to tending the gauges, things were all out of whack. The low side is pegged high, and when the compressor is on, the high side quickly (in about ~5 seconds) goes to emergency cut off at 450 psi plus, then the safety switch kicks in and turns the compressor off. Static, engine off pressures are Low side = pegged, High side = 150 psi.

After sitting over night, no change.

What's wrong here, and what's the fix???

Original compressor is an R4. Is your new compressor an R4 as well? Some aftermarket compressors are not the same.

Original Condenser was a serpentine unit. Was it replaced with the same type or a Parallel Flow unit?

Some GM liquid lines to the evaporator contain an orifice tube. If you added a second orifice tube at the evaporator it will act like yours seems to be.

Check your liquid line. The "extra OT is usually located at the condenser outlet.

I replaced the compressor with the same as original; R4 with serpentine belt. All new hoses etc., came set up for R134. Condensor is parallel flow. New lines came with orifice tube pre-installed in line that connects at condensor. Terrible place for it!!

I did not add another orifice tube, and when I flushed the evaporator it really gushed the fluid, so I don't think I missed one there. Before you ask, I used acetone to flush, as I'm out of real mineral spirits and refuse to buy the neutered stuff. It had a few days to evaporate before I assembled and vacuumed down the system.

Thanks for answering. What's next step? I'm guessing a clogged/defective orifice tube. Maybe... How do I check for system clogs? Can't run it, it's gonna blow!

Vettepilot

Recover and pull the OT for inspection would be the next step. Be sure the liquid line is clear. Sounds like you got the evaporator clean.

Check the condenser discharge fitting for debris

Well, guess what. Even though I tried to buy quality parts, they're all made in China anyway, and the A/C lines at the condensor were a really, really poor alignment/fit. You know where this is going, huh? Yep, I accidentally swapped the lines at the condensor, right where the Orifice tube is located...

Embarrassing.

So, lines are swapped back and vacuuming back down for an hour or so again right now.

THANKS!
Vettepilot

Yeah, that will do it. Glad you found it quickly.

Yes, that ERA of GM trucks had the same fitting on both the inlet and outlet of the condenser- easy to mix them up- seen it many times-- always remember that a condenser cools the hot gas in and it changes to a liquid as it flows downward to the outlet- where the OT usually is.