I used the A\C for the first time and it sure seems to load the engine when the compressor engages, cruising at 80 you can feel it go on and off. also seems to cycle to much. the compressor and drier were replaced not long before I bought it in Dec. I could understand feeling it on a 4 cyl but not on a V8. car is a 93

 

Definitely. I feel mine too (lt4) and it definitely lugs the motor a bit.

I switch it off before I hit it hard just because I don't like to spin it that fast, as u probably know, it is supposed to cut out at wot.



sam

 

Gator, the reply you recieved from Torchred is interesting, because I have a '96 as well and switching my A/C on or off hardly seems to affect my idle at all. Oh well, maybe mine is the odd one...

 

Usually a sign of a worn out compressor. For '90 and above, GM redesigned the system so that the ECM controls compressor engagement which pretty much makes the process seamless. Do make sure the compressor is tight and that all the supporting brackets are installed and that the motor mounts are in good shape. I'd then check the gap between the outer hub of the clutch and the pulley. Should be .020 inch. If it's too wide (and generally if it is, you'll hear it as well as feel it), you can reshim it with a shim kit. Before doing that though, take the belt off and after you no longer hear the pressure equalizing in the lines, turn the outer hub by hand which will turn the shaft. It should turn over with minimal resistance. If it's difficult to turn, time to replace the compressor.

GM specs for cycling (at idle) is less than 8 per minute at 70 degrees. Realistically, it shouldn't cycle at all at this temp (or higher) if it's got the correct charge. Below 50 degrees, it will probably be off more than it's on, but it still shouldn't cycle excessively. Better to check pressures with a manifold gage set. That will also tell you if it's plugged up (high side in excess of 250 psi) which can put a much larger load on it and cause it to cycle at speed.

Should it all check out - gap is right - charge is good - compressor turns over freely - then it gets a little dicier. A/C signal is on a data line from the Dash to the Programmer (Electronic Air) and then on to the ECM. The ECM notes the pressure signal (voltage) from the Pressure Sensor and throttle voltage from the TPS and then grounds the Compressor Relay a nano second AFTER it kicks up the IAC counts and by doing so, the idle matches compressor load when it engages. If that IAC circuit has too much resistance in it - or if the ECM is simply bad - then you might start feeling something. Really difficult to troubleshoot as most scanners can't capture data quick enough to see what's actually taking place; ie, it becomes a crapshot about what you may need to replace - ECM? Wiring? Dirty IAC? Compressor Relay? Fortunately (or unfortunately) it's usually the compressor or clutch assembly, so check those things out first.

 

PS - if you really want to get rid of it for good - maybe you're just super sensitive - adapt a variable displacement compressor from one of the many GM cars that use it. The system doesn't cycle and the compressor weighs less. Frankly, I don't know why GM stuck with the Nippo Compressor (and it's cycling orifice system) when for allmost everything else, it went with something a little less complicated.

 

thanks SunCr that is good info. the compressor is only a few months old and they may have the gap set to wide. it was replaced by the previous owner. I never noticed it in town driving, but once on the highway at steady cruise I could feel it. it may also be overcharged. I will hook the gauges and check. the A/C system works perfectly but to me it should not cycle that much.

 

Depending on where the compressor came from - it could still be bad. I bought a new "Factory Aire" brand for my truck from AutoZone that was broken out of the box - unfortunately, I didn't know that until I installed it and turned it on.

 

I purchased my 94 new, and I have always been able to feel the a/c compressor engage. It's even more noticable that my 2006 Cobalt.

 

I used to be able to feel mine.. then the clutch took a dump and I replaced the compressor and the clutch with new parts and converted over to 134a... I dont feel it anymore.. (or I should say it is faaarr less noticeable)

 

You really shouldn't feel much of anything after '90. Earlier Years don't use the ECM to engage the clutch and for those Years, the ECM receives the a/c signal about the same time the clutch engages so you do notice it. You'll note that GM says as much in every Service and Owner's Manual written up until then - but after '89, the ECM has load and TPS going in - so you shouldn't notice it. I didn't on either of my GM trucks - though the '97 S10 had an air gap the size of the Grand Canyon from the Factory and it always engaged with a loud thump (until I pressed it on right).

 

Its about a 5 h.p. load. When it switches on or off you may well feel it. Its most noticable in mine on the highway, low blower speeds. benny

 

Nope. Sorry, but I didn't say at idle. All I said was in effect that I agree with the OP, that I feel the engine lug when the compressor is either switched on manually, or cycles on and off. And the OP didnt imply at idle either, he specified at 80. Unless I misread.

This is the 3rd compressor in my car, the 1st two were on the lt1 engine, and the 3rd one came with the lt4 engine. I have always noticed the compressor lug the engine...any pump driven by the engine is gonna sap power. no?

 

It shouldn't be cycling at Cruise - Check charge and for a blockage, particularly if it's the 3rd compressor. Otherwise, stomping on it and feeling it kickout wouldn't be unusual.

 

I have a 95 and like the above post I have never noticed mine when it cycles, mabey I am lucky too.


Cruizer

 

I have a 94 and can always tell when it has cycled on, it sure pulls on the engine. I don't hear it, but I can feel it.

 

Yep, I can feel mine come on and off on both my C4's.
I have an '84 and a '91 can feel both of them...
The '84 is a more pronounced 'feel' than the '91.
I have a Sanden compressor on my 73 Chevy TPI truck and while it doesn't take as much power to drive it as the A4 or the R4 compressors, I can STILL feel it cycle when I'm going down the road.

I have a 98 LS1 Z28 and I CAN'T feel that one cycle.
Got a '02 Z06 and I CAN'T feel it cycle either.

The ECM bumps the Idle Air COntrol up at idel so you should not feel it then.
The OP posted about his st 80 MPH though.

 

I do not feel mine at all. I often wondered about that because I know the AC is working. Good job on that one GM. BTW, I have 1 1996 LT-1.

I recently had the entire AC system evacuated (removed engine). I hope it is the same when I get it back together