AC won't engage on 93 Chev Surburban. DOn;t know

Looks like the low pressure switch gets power from a 10amp ac fuse. Power then goes to the ac relay which is powered on by the ac heat controller on the dash. Power then goes thru the high pressure switch to the compressor. The ac relay is grounded to the body. Do you have power on the lite and dark green wires going into the relay and is it grounded ?

You need to have the refrigerant charge level checked, it sounds like it is low. You Need a set of AC pressure gauges to do this testing. If the system has a low charge the pressures will be very low in the low side testing port.

The most common cause of no clutch engagement is a low state of refrigerant charge in the system. Have a set of AC pressure gauges hooked up and bypass the compressor cycling switch and check the pressure on the low side charging port, you show shop 28-32 PSI at idle.

Hi Steve, Have the gas pressure checked in the system. If the pressure is low a safety switch will stop the AC from engaging! Regards John

it's either low (in spite of your readings) or your a/c clutch is not working correctly or you have too big an air gap in the clutch.
First, just disconnect the 2 pin connector from the a/c pressure cycling swithc and jumper the 2 pins with a wire to force the clutch to stay engaged. See if it blows cold then, and stays engaged. You can run this way for about 15 minutes before you have to pull the plug.
report reulsts.

please don't forget to rate.

you can run the compressor for a few minutes to see if you get cold air with the low pressure switch crossed out. if you don't have cold air after about 5 minutes then you still have a leak somewhere.

I think you have a low pressure situation. To prove or disprove, find the pressure switch and short it out (so the system thinks the switch is indicating sufficient pressure). You can have near sufficient pressure ("OK" pressure) and you can have cooling but your system knows if it is low or not.

My AC worked fine, I thought. It cycled on and off very rapidly - I thought this was normal. It is a 'new' vehicle to me. Pressure was 'ok' but not perfect. When I added one can, it made a world of difference. Mine is a 1994, BTW. I am certain some freon had gone from the system.

I don't think the computer controls the AC - but don't know this for a fact. I suggest you have this system checked by a automobile AC pro for best results.

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Lots of things can cause this, I will list them, easiest first.

A blown fuse or relay can prevent the clutch from kicking in. Low refridgerant charge will also do this, the low pressure switch will prevent the clutch from engaging when there is low refrigerant to prevent damage. You may need to put more in, and you also may need to jump the low pressure switch to get the compressor going to add more in. Very rarely the controls could have gone bad, which are the buttons on the dash. Id check out the fuses, relays, and pressure in the system first. A shop may even do a free diagnosis for you.

If you do not have enough refrigerant in the system. The low pressure switch will prevent the compressor from engaging to avoid damage.

Check your pressure.

I don't recommend this, but you may need to jump your low pressure switch to get the compressor going to add more refrigerant to the system. But if your low on charge, it may be "best to take it to a shop to have them fill the system".

There is a better than not possibility that your compressor will not engage due to low pressure in the system. You should be happy about this because if you run it with little or no freon in it, it could be damaged.

You can prove this by shorting out the low pressure switch normally found on the passenger side on a coolant line. If you short it out and it runs, low pressure is the trouble.

I suggest you have your AC serviced by a pro - why? You have a leak don't you? (where did the freon go?) Do you have the equipment to find and repair the leak? A pro will know what to do and how to do it. When he or she is done, your AC will work great.

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