I don't get how this could be, but today I tried to use my A/C (almost 70 outside today, but the truck was parked in the sun, so it was hot inside), which worked so well during the summer (made the interior feel like a fridge), and all I got was warm air out the vents. Tried FULL cold and recirculate button, no change.

The actual A/C compressor clutch on the pulley wasn't engaging when I press the A/C button (orange light on the button is lit, but no change in engine RPM, cold air out the vents or the compressor clutch locking in). This was one week after the car had to get a new intake manifold gasket (slow external leak).
What is so funny is that both HVAC fuses and the A/C fuse are good (fan, heat and HVAC controls work ok), the A/C relay is ok (tried a new one: no luck), just recharged the system last year with R-134a, new serpentine belt put in when the IMG was replaced and there are no visible leaks in the A/C system.
What is also so funny is that there is NO VOLTAGE (just the electronic multimeter numbers dancing in the mV scale (open circuit). The multimeter is working properly also because it shows a strong 12 V at the battery )at the A/C compressor connector near the serpentine belt pulley when the A/C is commanded "ON" when the engine is on or off. Obviously must be an electrical malfunction, but I can't find anything wrong with it. What else could it be? Only other thing wrong is that I had a short in the power door locks a couple weeks ago and had to pull the LKS/MIR (5A) fuse so I didn't have to contend with that. Could that be related? Worked fine last summer and before the IMG repair. Wonder if the repair and the inop A/C could be related. Now I know not to trust some of the local, small town mechanics here if the IMG repair caused the malfunction.

 

Here is another test you can try. This is to make the system think that you have A/C in the system.

Disconnect the connector from pressure switch.
Jump both pins with a paper clip on the electrical connector
Have someone watching the A/C compressor while you start the truck and turn the A/C on. If the compressor cycles on, turn it off.
You now just narrowed it down to either low refrigerant or a bad pressure switch.

 

You did remember to plug in the high pressure switch on the back of the A/C compressor during the IMG change right...?

 

i agree with them ^ probably a low or high pressure switch faultry or even just unplugged

if faulty hopefully it is the low pressure switch (located on the accumualtor i think) which can be replaced without leakng/discharging any freon

if its the high pressure switch on the back of the compressor your looking at more money and maybe even having to take it to a ac expert

low pressure switch went bad on me and after a trip to the junkyard and $2, it was working great again

 

Did your test, compressor spooled up no problem and stayed on, so i shut it off after a few seconds. I thought it might not actually be the switch because it was working great before the repair and during the summer, so I thought for some reason it just might be empty. I got the R-134A hose and refill kit. Plugged it in the low side: 5 PSI with barely a hiss!!!!! The darn thing was empty. Can't believe I didn't think of that possibility before even though we refilled it last year and found no leaks. Even my grandmother asked me "Could it be empty? Doesn't it need "freon"?" Maybe they evacuated the system when they replaced the IMG and not only didn't refill it, but didn't tell me about it........ Used nearly 2 12 oz cans and filled it. A/C now works GREAT. The pressure gets to 45 PSI, the compressor kicks on, drops to 25 PSI, disconnects, rises again and repeats. I assume that is how it works? The compressor kicks on just before the yellow zone on the gauge. Thanks for all the help to everyone who helped on this problem.

 

If the bottom (belly) of that compressor is oily/greasy- there is your leak- HT-6 compressors are known for belly leakers- 96-2000 model years especially....

 

Went out to check the A/C system after I read your message. I tried it again and it was only 41* F, so the air was cold anyway (out the vents), and the compressor stayed off. 5 min later, it was 40F and it didn't even let me select A/C on the HVAC control.
I checked the pressure on the "can" and it was steady at around 40 PSI. I also checked the compressor. Aside from alot of dirt and 11 years of surface rust, the compressor shell was dry all around and under it. I didn't see any liquid under the compressor either and the bottom felt dry. I thought "Why would this thing have an A/C COMPRESSOR leak at 717** miles???". There doesn't seem to be any leaks in the system, nothing on the hoses or anywhere else in the A/C system. Just an honest mistake by the mechanic that probably wanted to play it safe by draining the system before removing the compressor (and possibly bending or even breaking the hoses, which it doesn't take a computer geek (guilty ) to know that anything that uses thick rubber hoses to function is probably under high pressure and is dangerous if mishandled.) before replacing the IMG, but forgot to refill it or even write on the repair bill that they did that and has to be recharged. I didn't originally suspect a leak because I used the A/C frequently from last April-October on very hot days with no failures.

Thanks alot for the tip because if I have any future problems with the A/C, I know another possible place to look to diagnose it further.

ComputerNerdBD

P.S. Please see the photos. Sorry for the low quality. I took them on my cell phone. Also, if you are wondering what the bundle of 1/4 tubing is for in the last photo, it is for the Star Trek horn I am hooking up. The horns and wires are in, but I haven't had the time to install the compressor yet.

 

The mechanic did not empty the system since you are showing pressure in the system.. it takes 47 psi to engage the compressor- it is still too cold for you to test. A/C static pressure will increase with ambient temp-- so try it again when it is above 60 degf outside- see what happens...

 

He said it was basically empty in a previous post and that he put 2 cans of R-134A into it.

ComputerNerdBD,
I hope that this works for you. I have always pumped a system down and made sure it held vacuum overnight before recharging. Especially if the system was opened up.

And in all of the IMG I have replaced, I have always just laid the compressor over on the passenger fender and secured it, not disconnecting anything. I have done this on quite a few Blazers for family and friends and they are still working perfectly after a number of years since the IMG repair.