A/C compressor won't engage

just replaced my a/c compressor & getting my system changed to the newer freon setup & installing a resistor that was connected to the fan, but when I push in the A/C button (the light goes on) but apparently the air conditioning compressor is not engaging, i.e. I’m not getting cold air. We are now ordering a new panel (pushin)switch @ $100 and are going to have to pull the dash out to install this switch. Is there something else (cheaper) that we c=should be checking first? My mechanic says if installing the new switch doesn’t solve the problem he is not sure where to go with this next. Any suggestions.

This may seem overly obvious, but have you had the system charged by a properly skilled technician at an independent shop? Not having a proper charge in the system will not allow the compressor clutch to engage. You cannot do this properly on your own with cans of refrigerant from the auto parts store. Some quicky lube places offer a/c recharge, but that is not an option IMO. A/C takes a lot of skill to become reasonably skilled at diagnosis and repair. Even working with a 20 year veteran of automotive a/c, it took me a couple of summers of diagnosing and repairing a/c systems to become comfortable with doing this kind of thing professionally. The first thing I would do in your situation is to evacuate the system, make sure it holds vacuum for at least 20-30 minutes to rule out a leak, and recharge it with the proper amount of refrigerant with a calibrated scale or modern a/c machine. That may be all it needs, and is much less frustrating than dismantling a dashboard.

You didn’t say you evacuated (vacuum pumped) the A/C system for 30 minuets. You may be able to rent an A/C vacuum pump from a tool rental store. Find out by calling.
The A/C compressor won’t come on until there is about 40 psi of refrigerant (R134). Do you have the service gauge set for R134? It’s one of those “gotta haves”.

I did not do this myself. I took it to a mechanic who has been in biz doing car a/c for 40 yrs. I will mention the evacuation and the vacuum/leak part, although I believe he did this.

Thank you so much for your input.

Hello, I am having the same problem with the compressor not engaging. Will having the a/c system overfilled cause the compressor to not engage either? at first I had thought it might be a relay not causing it to engage, but after reading this I’m not sure.

It depends on what car you have. Some do lock out on over pressure too, but not all of them.

If your mechanic has an ohm meter, he should be able to rule out that switch very quickly rather than throwing $100 bucks at a guess.