Help with AC system

[turboman38]

My AC compressor is cycling too often. It blows cold air but only runs for 5 to 10 seconds so it doesn't stay on long anough to cool the inside of the car off. Tried to put a can of Freon in it but it would only take a bout 1/4 of the can so I assume that's it full. Anybody know what could be wrong?

One more question. When I move the knob to Max AC it takes a long time for the actuator (or what ever it is called) to switch the box so that the air comes out of the vents. What causes this?

 

[scottyb]

You'll need a set of gauges to determine what is going on with the freon. Mine cycles off when the low side gets down to 20. I added some freon to limit the cycling. Now it only cycles a few times on startup, or when it's not really hot outside. There's a good link on gnttype.org about adding freon, pressures, weight, etc.

Low vacuum usually causes the vents to be lazy or inop. There is a small 'vac distibuter' (vac switch, shaped like a disc) on the back of the AC control head in the dash. I removed mine, disassembled it, added a small dab of grease to the surfaces, and it works much better now. Before I did this, it wouldn't even switch to the dash vents when I put it on 'normal' AC. This part is also available at any GM dealer for ~$20 or less. Also make sure you have no vac leaks along the vac circuit leading to the AC unit. It shares the vac source with the cruise control and the EGR. Last, make sure the vac line is connected to the heater control valve.

 

[BlackBandit]

In addition to what scottyb said about using the manifold guages to make sure the proper amount of freon (or whatever) is in the system, I believe the pressure switch on the evaporator has an adjustment screw. If you unplug it you should see it between the plug blades. You can use that to set the pressure the pump turns on at. HTH

 

[scottyb]

The compressor cycles off for a reason. The low pressure switch protects the compressor in the event of low freon. Don't go adjusting things unless you know what the deal is.

 

[BlackBandit]

The compressor cycles off for a reason. The low pressure switch protects the compressor in the event of low freon. Don't go adjusting things unless you know what the deal is.

Couldn't agree more. I didn't mean to imply you should band-aid a problem with the switch. Just meant that the adjustment is there if it's needed after you set the freon level.

 

[tminer]

The compressor cycles off for a reason. The low pressure switch protects the compressor in the event of low freon. Don't go adjusting things unless you know what the deal is.

I agree. You can check if that switch is cycling the compressor and if so try replacing it. You can buy the replacement switch for about $15. I've had to replace it on both of my LC2 cars. It's called something like the high pressure compressor cycling switch. It screws into a Schrader valve so no need to evacuate the system. The last replacement did not have an adjustment and the TTA Service manual never mentioned an adjustment procedure that I can recall. This was done last Saturday.

HTH,
Tom

 

[gbsean]

Pep boys has the switch....I evacuated my system and convereted over to 134A. If the compressor is cycling on and off alot and the system is pressurized change the switch. Before i change the switch you could actually wiggle it and make the ac compressor go on and off.

 

[MBKBJB]

Had the same problem with issue resolved today

I had the "exact" problem you are having and we figured it out today. On the high pressure side of the system there is an inside filter that keeps things clean (was definitely doing its job). This filter was completely clogged causing the compressor to cut in and out repeatedly with very short bursts of cold air.

Also, we were having issues loading freon in the system just like you described.

Replaced filter, reloaded system back up and now the A/C works terrific!!

Hope this helps.

 

[84GNGary]

Turboman38,
It just sounds like you are low on charge most likely. It could be a high side restriction that MBKBJB mentioned too. If you could only get a limited amount of freon out of the new can it was most likely caused by charging the system with vapor, then the can starts to sweat and get cold. The pressure in the can then equalizes with the system pressure and then the charging process stops. You can avoid this by charging SLOWLY with liquid by inverting the can. If you are using 134a it should only be charged by liquid anyway. I would try a can or two you should see your suction press rise and the suction line start to sweat back to the compressor. Sweating is a good sign you do not want to see frost going back to the compressor. Also the compressor should stop to cycle. Keep the engine around 2000 rpms and A/C on high max cool when charging and your suction press should be in the mid to low 20's.
One last thing if you already converted your system to 134a DO NOT BUY THE CONVERSION CANS WITH OIL IN THEM ANYMORE, JUST GET THE CANS WITH REFRIGERANT 134a ONLY. Because when you use them and charge with liquid you are adding more oil to the system. Oil is a lubricant not a refrigerant and too much it will reek havoc on your system.

 

[84GNGary]

Turboman38,
I just seen the bottom of your original post. If you are getting poor or no air flow across the A/C evaporator coil due to your vents not working properly it will cause the same problem too.