My AC blows ice cold air...No complaints there. But, when I have it on, while I'm driving I can feel the car "bucking". I think the compressor is coming on/off every 10-15 seconds, and when it does, you can feel it. It's the worst when cruising at about 2,000RPMs, but you can feel it higher/lower. Even though I'm blowing cold air, could I still need a re-charge?? Any tips would be appreciated.

:cheers:

 

if compressor goes on and off every 10-15 sec you`re low on freon... :yesnod:

 

Cool, thanks. I guess I was just a non-believer there because it's blowing cold.. I'll have it looked at. How often, when it's charged properly, should it come on/off??

 

My AC blows cold enough however it seems the blower fan doesn't push very hard. Since I never owned a Vette before I don't know what is normal. Should it be like a wind tunnel at the highest fan setting? Mine feels like it goes no faster than what I would expect between a medium and low setting.

 

Wish i could answer that question, but I havent had working a/c in over a year :banghead:

 

I never paid attention to the time...but I can feel the compressor kick in on my 96...its not a big drop but definetly can feel it.....Ill have to time it next time I drive it....and its always been that way.......
:seeya

 

Disconnect the blower harness and jumper it to the battery. If it blows stronger, something is wrong. Is it manual or electronic air?

 

It is electronic.

 

Blower speed is controlled by a module bolted to the Evaporator housing on the firewall. Depending on year, it gets low voltage signals from the control panel or the programmer and amplifies them to control blower speed. The operating inputs are usually 2 (low) to 7 (high) volts. Output is 4 to 12 volts. If the blower runs faster jumpered to the battery, you'll need to check the input to the module. It's usually a brown or tan wire - the others will probably be: red - power; purple - output to the blower; black - ground; green and dark green/orange - compressor control.

 

I have the same exact problem. Ice cold air. Loud fan noise, little air flow. What gives??

 

If it's making a noise, suspect a bad motor, squirrel cage or some sort of blockage in the heater/ac plenum. Is heat more powerful than a/c? If so, the evaporator may be plugged up with debris or it may be leaking gas which destroys the foam filter and gunks it up (if you recently had to add some gas, that may be where it's going). Otherwise, jumper the blower to the battery and see if the output improves. Post your results and whether you have manual or electronic a/c for addt'l help.

 

Here's another problem in a 90 with electronic air. It comes on when it should and is cold but blows mostly on the windshield regardless of what buttons I push. I'm getting a lot of condensation on the outside of the windshield. Last summer it worked fine. Ideas?

 

GM HVAC applies vacuum at all times to the defroster door sucking it shut. No vacuum, and all you get is defrost. Follow the vacuum fitting on the right side of the plenum (next to the fuel pressure regulator) to the left side of the engine near the distributor. There is a check valve there and it tees off to the interior of the car with the other side running to the vacuum storage tank in the left headlight well. Make sure this line and the check valve are intact. If it's ok, you will need to access the programmer above the accelerator pedal. This little jewel distributes vacuum to the HVAC doors based on inputs from the control panel. You will need to remove it to check out the vacuum source from the engine. If vacuum is present, then the programmer is probably kaput.


[Modified by SunCr, 2:45 PM 5/27/2004]

 

OK, I'll be the wet blanket. If you are driving along at 2000RPM (I'd guess ~70MPH), I really doubt you could feel the A/C compressor cycle. You might see it at idle at 2K.

My guess is you are experiencing the initial stage of Opti failure. This is a pretty common symptom. Next stages are more pronounced miss at speed and jumping idle rpm.

 

John, I've got a 6 speed, so 2k RPMS could be any gear.. In this instance, I'm referring to 3rd gear cruising around 30-35MPH.

I'd CONSIDER it to be an opti problem if it did it with the AC ON OR OFF, but, it's only with it ON. When it's off, the car purrs... :smash: Plus, when it 'cuts' out a little bit, I can hear the AC cycling on/off under the hood.

You are right though, on the highway, in 6th, I don't feel it. It's mostly low speeds under a load.

 

It sounds like the same problem I have with my 1992 Corvette.

When I am driving, it "feels" like the AC compressor is switching on and off about once every 10 to 20 seconds. My temporary solution has been to just not use the AC.

Worse case, if no one has a solution, I need to take the Corvette to the shop in the next few weeks anyway, I will find out what the deal is with this surging problem. It will be a few weeks though. Hopefully before then, someone will reply with a solution to your problem.

 

There are 2 pressure control switches on the system that will cycle the compressor to protect it if the freon is low or if the car is at extended idle (stuck in traffic) to save gas. One is close to the top of the evaporator and the other is on the thiin tube going to the condensor from the evaporator.

I have had to replace the lower one because it was stuck at a low pressure setting. There is also an adjustment screw in the switch wire connector that lowers the pressure that the unit will shut off at. I had to have mine adjusted to run R134 in my 86.

In any event, its best to have an reputable AC tech check the system before making any adjustments. The freon and oil levels need to be correct before anything else. You could mistakenly mask a problem that will cost big $$$$ down the road.

 

At idle - extended or otherwise, the compressor should cycle less and if the system is charged correctly, it shouldn't cycle at all (if it's much above 65 - 70 degrees). Anytime there is reduced air flow across the condensor operating pressures will rise and pretty much stay above the cutoff threshold (25psi for R12; 22.5psi for R12). If it's cycling at idle, it may be low on gas, or the orifice could be plugged up (and it easily could be if nothing has been serviced in 10 to 15 years).

Up until '90, most will feel the compressor cycle at idle as the ECM gets it's a/c signal from the compressor or the a/c control panel. That creates just enough of a delay for the IAC to be a tad behind compressor clutch engagement. For '90 and above, GM redesigned the system so that the ECM controls clutch engagement giving it much better control over idle quality.

At peak efficiency, which for an a/c system is anything above an engine speed of 1200 - 1500 rpms and a vehicle speed of 25 mph, the clutch may cycle as the increased air flow across the condensor reduces system pressures. It would be unusual to feel this as the load on the engine is no more than 1 to 2 hp. If it is felt, suspect other problems such as a worn compressor or compressor clutch or a plugged up orifice. I wouldn't necessarily consider it a low charge - particularly on a 90 or up where the ECM will shut down a/c operation if the pressure switch sends a voltage signal indicating a low charge and for these later years, set a trouble code. In any event, debris in the orifice raises the high side; reduces the low side and you won't get a trouble code because the pressure switch signal to the ECM is on the high side.

If the pressure gets too high - above 425 psi, the switch is going to shut it off to keep it from blowing up.

You should be able to reproduce excessive cycling in the garage. Hold the throttle open with a washer so that the engine is running at 1200 to 1500 rpms. Get the fan running. Up until 89, you can disconnect the fan switch on the high pressure line. For '90 and above, both fans should allready be running, but if they're not, ground the relays so that they stay on. You can also put a fan in front of the car, but with a bottom feeder like a Vette, it doesn't do a lot of good but you need to get as much air as you can flowing across the condensor. In any event, if the compressor cycles more than 8 times in a minute, there's a system problem.

Once it's cycling, observe the clutch for slippage (On the '92 and above that might be little difficult but you need to get a good look at it). If it is slipping, check the air gap with the engine off. There should be a clearance of .020 between the drive plate and the pulley. Any greater and it increases compressor load (and wear) and it will also make a much louder noise when it engages.

To see if the orifice is plugged, you really need to see what the pressures are. Otherwise, look for ice on the high side line 3 or 4 inches before the evaporator or just below and around the nut that connects the high side line to the evaporator (it's the line at the bottom). Feel the line where it enters the evaporator (right where the line enters too - much higher and you can burn your hand) along with the top line. Both should be cold with the upper line maybe a tad cooler. You can measure the temp with a digital meat thermometer if you want. The temp isn't terribly important, but both should about the same and below the outside air temp. Post what you find out/observe for addt'l help.