Engine surging when A/C is on

[92ShoOff]

So after replacing an overpressurization valve on my A/C system on my '92, I serviced my A/C with gauges and ended up using nearly two full cans of R134A. As soon as opening the valve on the cans of refirgerant the needle on the guage would go to the red zone on the guage and very slowly climb its way down. So after two cans the vents were blowing out at 40 degrees and the guage needle was in the blue zone. So it seems as if the system is charged properly.

Only problem is when I kick on the A/C and the compressor comes on I feel the engine sort of "surge" while accelerating and steadily driving. Like the motor softly jerks, and even when letting of the gas and slowing down you feel it **** back a little. I mean it's not hard jerking/surging-- it really is pretty gentle. Regardless I know this is not supposed to happen. Anyone know what would cause this?

The compressor WAS "short-cycling" after I first serviced the system, and I haven't tested it to see if it was still doing this since two weeks ago... but I replaced my EATC with the updated hard-button version and the compressor doesn't seem to be short-cycling anymore. I don't know if this is because my old EATC had something wrong, or if the problem just went away on it's own since the last time I tried using the A/C. But if I recall, the engine was doing the surging while driving when I had the old EATC in weeks back... probably a little worse than it does now but I'm not sure because I only took the car out on the road for a few mins with the A/C on and turned everything off because the compressor was short-cycling. So like I said, I don't know if swapping units had any effect on this, or if something cleared up since I first tried using the A/C two weeks ago... like maybe the system was slightly over-filled and since then maybe some refrigerant has leaked out and is now closer to the proper pressure.

 

[sdpatt]

The short cycling was due to a low refrigerant pressure. Adding two full cans more than likely overpressurized the A/C system. You should check the static pressure of the system when the engine is off and has cooled down overnight. The A/C pressure gauges will have a scale that displays the desired pressure of R134a for a given atmospheric temperature. The engine and A/C system must also be at this temperature for this scale to be applicable.

My retrofitted R12 system, now using R134a, likes a static pressure of aproximately 95-100 psig (pounds per square inch, gauge) at an ambient temperature of 85F. For lower temperatures the pressure will be less and the opposite wil be true for higher temps. At 70F, the static pressure in my system is about 85 psig. This charge level is capable of producing 32F-35F discharge temperatures on a 95F-100F day during a long highway trip when the system has achieved maximum efficiency (many miles).

The load of the A/C compressor engaging requires approximately 10hp to overcome. There is no way to hide this drag on a 3.0L or 3.2L engine that is producing only 30-50 horsepower to cruise down the road. You will feel the compressor engage/disengage if you are paying attention.

 

[92ShoOff]

Ouch man, you REALLY know what you're talking about. Haha. And your description of everything is perfect, and now I know exactly what my problem probably is with the short-cycling and exactly what pressure everything needs to be at. Man you're excellent! Thanks a bunch!!

 

[Xs SHO 1]

The short cycling was due to a low refrigerant pressure. Adding two full cans more than likely overpressurized the A/C system. You should check the static pressure of the system when the engine is off and has cooled down overnight. The A/C pressure gauges will have a scale that displays the desired pressure of R134a for a given atmospheric temperature. The engine and A/C system must also be at this temperature for this scale to be applicable.

My retrofitted R12 system, now using R134a, likes a static pressure of aproximately 95-100 psig (pounds per square inch, gauge) at an ambient temperature of 85F. For lower temperatures the pressure will be less and the opposite wil be true for higher temps. At 70F, the static pressure in my system is about 85 psig. This charge level is capable of producing 32F-35F discharge temperatures on a 95F-100F day during a long highway trip when the system has achieved maximum efficiency (many miles).

The load of the A/C compressor engaging requires approximately 10hp to overcome. There is no way to hide this drag on a 3.0L or 3.2L engine that is producing only 30-50 horsepower to cruise down the road. You will feel the compressor engage/disengage if you are paying attention.

2.5 lbs of refrigerant in the system ring any bell?

 

[sdpatt]

2.5 lbs of refrigerant in the system ring any bell?

My converted R12 system does not have a placard stating how many pounds of R134a are to be installed. Since my system was sized for R12, it is not directly replaced by the less efficient R134a.

If the system is not completely evacuated by a vacuum pump, there is not an accurate way of knowing how much refrigerant is remaining. The total charge value (ie. 2.5 pounds) for your system is only applicable for an evacuated system. Please don't talk down to us.

 

[92ShoOff]

Who's talking down to who??? Anyway, my system was drained of the old R12 before I converted it over to R134A. I don't know exactly how many lbs. were added during the service though because my dad was the one who did everything. I'll see if I can't find out if it's over-pressurized or not and fix the problem. Thanks everyone.

 

[drdave]

An aged AC clutch will also produce very undesirable surging with a little chirp! You feel this even when you're not paying attention.

 

[projectSHO89]

Who's talking down to who??? Anyway, my system was drained of the old R12 before I converted it over to R134A. I don't know exactly how many lbs. were added during the service though because my dad was the one who did everything. I'll see if I can't find out if it's over-pressurized or not and fix the problem. Thanks everyone.

R134A requires typically 80-85% of the amount of R12 as measured by weight. Find the R12 label and do the math to find the correct amount of R134a to use.

Once an system is opened, all the refirgernat will be lost. However, the volume of any remaining oil will affect the resulting charge.

Steve

 

[92ShoOff]

Hmmm... I think I was hearing a chirp when I had the music off and the windows down while the A/C was on. I think it was when I started off in first gear and did it again going into second possibly. I didn't know if I was hearing things or not.... but I guess maybe the clutch was chirping. So what would be the resolution to this problem? Can I just change out the clutch somehow... or do I have to replace the whole thing?

And by the way, I wasn't being ignorant on that reply to sdpatt, everyone... I was being completely serious about how he really knew what he was talking about. I wasn't laughing to make myself sound like I was being sarcastic... i was laughing at the fact of how awesome this guy is coming in here with all of these figures and knowing this stuff down to the "T". Most people don't give answers like he did.... he told me ALL of the details. Thanks sdpatt!!!