Birdman01

Hello everyone here at the forum. The ac system in my chevy truck is not working,just blows hot air. A few weeks ago I noticed that the air was not cold enough so I put in a can of R134 in it and started to get cold again. Yesterday,it was about 90 degrees here in town so put the ac on but nothing but hot air again.When I turned the ac switch I did not hear the comp. clutch engage so went over to check and its not engaging at all. Normally when its been low on freon,the clutch just keeps cycling in and out but this time,it does not engage at all. Does anyone here have any troubleshooting charts for the ac system on my truck that I can get to troubleshoot the compressor and components? Thank you kindly.

oldchevy

When your system is low on freon it will cycle on and off. When your system gets real low on freon it will not cycle on and off anymore. It will just stay off. You apparently have a leak since you just had to add a can of freon. Put 12 volts directly to the compressor clutch and see if turns on.

Birdman01

Thanks for your reply. I have been trying to diagnose the problem,checking voltages and continuity. There is a switch connected to what I think is called accumilator/dryer. I checked for 12v with a probe at each wire (with ac power on) there is 12v at one wire but none on the other. Without a diagram,I can't really see how this system works but since its a switch, I would assume that this switch would supply power to the other wire and cause whatever component to activate, for example the clutch on the compressor in this case. I don't believe in changing parts without being 100% sure which part is the culprit but in this case,I don't think this part is very expensive so I'll probably just take a chance and replace it and see what happens.

Birdman01

I did some research and found out that the name of the switch is called the low pressure switch. Like i said before, compressor clutch was not engaging at all. I checked the voltage on the connector at that switch and it had 12 coming in but nothing going out,which activates the comp. clutch. ( I think it does) So,I removed the connector from the switch and jumpered the 2 pins together and as I did that,the clutch would engage. So, I thought It would be a faulty low pressure switch so I bought one and installed it. Well, I still have the same problem, clutch still not engaging at all even with the new switch. I checked the voltage at the connector that is in front of the compressor and there is 0 volts. If I supply 12v to that connector, the clutch will engage. So, the problem is that the comp.is not getting power to it so that the clutch can get started. Could it be that the accumulator has a problem and is not letting the switch turn on? Another words, going into shutdown or like when a load has a short in it and causes fuses to blow or something to that effect. Don't know much about AC at all but trying to find the problem before it gets too hot around here, usually about 115 degrees in the summer. Thanks to everyone for any and all the help I can get.

oldchevy

When you put in the freon, how long did blow cold air? You apparently have a leak in your system and if you have to add freon frequently to keep it cold, this is not a solution You will have to find the leak and repair it. You try putting some dye in and find the leak yourself or take it to a shop to get it fixed. .

Birdman01

This morning I put the gauges to see what kind of pressure was on the low side and its reading 30PSi,indicating to me that there is enough refrigerant to get the compressor going I would think. I also removed the connector going to the front of the compressor and supplied 12v to it and I can see where the clutch engages so that would indicate that the clutch coil is ok. I have a question? Does the comp. clutch get its power from the low pressure switch or does it get it from a relay? I know that the Low pressure switch has 12v at one of its wires. If it gets the power from a relay, than I should be checking to see if its energizing or not. The compressor, accumulator,and the orifice were all replaced 4 years ago so they are not origional and not 28 years old. When looking for refrigerant leaks,I don't use the dye,I have a tester ( Sniffer) that will detect when it finds a leak and sound the alarm off. I have plenty of time in my hands since I am retired and need to stay busy.
Thanks for your good advice, I appreciate it very much. Do you know where I can buy a wiring diagram for this AC system thats on my truck?

oldchevy

You already stated that you jumpered the 2 wires at the switch connector and the clutch engaged. This tells you that it is not a wiring problem. It is a problem with pressure which could be a bad switch or maybe your gauges are not accurate. i know you already replaced the switch but new parts can be also be bad or you were sold the wrong switch.

Birdman01

Thanks for your help and advice CF on this problem. Yes, I do have a new pressure switch but like you stated, new parts are bad too. I will take this part back and get another one and hopefully, will fix the problem. Will keep you posted.

Birdman01

I replaced the low pressure switch again but it made no difference at all. I borrowed a different set of manifold gauges and with those gauges the low pressure reads 30psi. I wonder if maybe the high pressure switch is in lock out and not letting the clutch engage. Where can I find the high pressure switch? I checked the A/C relay and it checks ok. The clutch is not getting any power at all. Should it have 12v all the time as long as the A/C switch is on or does it only have 12 volts when the clutch engages? Also, will any damage come to the compressor if I supply 12 volts to the clutch coil to get it to engage and see if I get cold air? This would tell me for sure if I have enough refrigerant in the system. Thanks again for your help.

oldchevy

You stated that when you jumped the connector to the low pressure switch that the clutch engaged. This means that nothing else is keeping it from working. Your problem seems to be that the switch is not reading enough pressure in the accumulator. Maybe more freon might help, if not maybe replacing the accumulator and orifice tube.