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A/C doesn't work, fans operate


sahls01gmc

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Hey guys, I'm having some problems with my A/C. I searched for the better part of 2 hours, but couldn't find a similar thread to my issue. I replaced the compressor, accumulator, drier tube and all associated fittings/gaskets/o-rings about 2 years ago. I haven't driven the truck recently, and even those few times I didn't use the A/C until recently.

 

The A/C doesn't blow cold, but all of the dash items do work as normal. When I push the snowflake, the compressor doesn't kick on. I checked the freon level, which apparently was empty. I ran a vacuum on the system, and then attempted to add freon. I was trying to put in the recommended 1.8lbs, but I was only able to put in 0.3. Here are the questions that I have:

 

- How do I test the HPS to make sure that the compressor will turn on when it's suppose to?

 

- What would cause me not being able to add more than 0.3lbs into the system?

 

- Is it possible that the malfunction is in the dash switch? How would I test that if so?

 

- Is there anything else that I am overlooking?

 

 

Please don't post "take it to a shop". I posted in the section because it said to ask only questions that I would go to a dealer for. I'm an excellent parts changer, just need some help from a fellow mechanic!

 

Thanks in advance for all of your help. This site has saved me more than once!

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4 answers to this question

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If you disconnect the pressure switch and connect the two terminals in the wiring socket together, the compressor should engage. It will not disengage though, so watch the pressures.

Are you trying to fill via the low side or high side? It has to go in the low side, and you should hold the can upside down to fill. An empty system that is still under the vacuum should be able to just about pull the entire first can in without running the system at all.

 

You say you checked the level and it was apparently empty. How were you testing the level in the system? If the system even contains a few ounces of refrigerant it will show a pressure on the gauges. If the system was properly charged when you changed all those parts a couple of years ago, and now it is completely empty, you have a leak. It will pretty much have to be a hole somewhere. A seal will generally not leak to a pressure under 10psi.

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Thanks for the reply Doug! I fixed everything via "shadetree mechanic" in the driveway. I used just about 2 cans to fill the system, and didn't vacuum the system first (I realize that I should have......). Worked great until now. I hooked up the truck to our A/C machine at work. It's a Mac Tools brand, but I'm not sure on the model. You hook up to the high and low side, and you can do just about anything from there. I first did a "recover", and it said it did not recover any freon. So then I did a 5 minute vacuum on the system, and it seemed to pass. I know it will tell me if it didn't. Then I attempted to put 1.8lbs in, but it only put in 0.3. At first, it only put in 0.17 and told me it slowed down, and to try again with the A/C turned on high. I did that, and it brought the total up to 0.3lbs. The pressure was up around 100psi on the low side (can't remember exactly at this point). I remember when I did it myself with the cans I had to have the A/C running while I pulled the trigger on the cans.

 

Are you saying the pressure switch on the compressor itself? Just making sure I'm tackling the right one.

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Generally the pressure switch on the compressor is the high side blow off safety switch. There should be a two wire switch somewhere on the low side. Used to be in the receiver/dryer. It may still be. Static pressure of refrigerant depends upon air temp. Does not matter how much is in the can, one pound or one ounce, the pressure is the same. Don't have enough exposure to the non R12 systems to know what static pressures are, but, in R12, static pressure is generally equal to air temp, with the high side being double ambient air temp when compressor running.

 

I am from the pre-machine era. Used to run a vacuum pump for 30 minutes after system was empty, and then let it sit for 10 min to make sure it held vacuum. Most times if it did not hold vacuum after the repair it was the line o-rings on the vacuum pump, or schraeder valves that were leaking.

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