QuestionI just converted my a/c to R134a from R12 as I assumed it was low on refrigerent.When I turn the a/c on the a/c symbol flashes on the electronic heat/a/c control but the clutch does not engage.If I jump the clutch out to battery it comes on and the a/c works well.The pressures are ok too.can you tell me what to check.I also jumpered out the pressure switch to check it and that did not make a difference.
AnswerSteele,
The first thing I would check would be the A/C clutch fuse.
It sounds as though you have a good understanding of what you are doing so I will give you the basic run-down of the wiring on the A/C system, without going into too great of detail. If you need me to go further into it, by all means, just ask. But before you start checking voltages and jumping items, make sure all of the plugs/connectors are tight enough to make a good connection. That seems to be the majority of the problems I am seeing this year, simply bad connections inside plugs. Ok, here's the general layout...
The switch inside the control head sends power to your thermostat. It sounds as though your control head is doing what it is supposed to from the light coming on. Your thermostat, providing the interior of the car is above the temperature it is set for sends the voltage forward to your a/c clutch relay coil and finds it's ground. This energizes the relay coil and the contacts close sending 12 volts to your low pressure switch. with refrigerant in your lines, you should have enough pressure to close the contacts within it, sending power to your high pressure switch. Providing your high side pressure is not above 380-420 psig, your high pressure switch stays closed and sends power on to your compressor clutch. Clutch energizes by finding its ground through it.
At all of the points above, you should read 12 volts, and you can bypass or jump them all for the purpose of troubleshooting. Don't leave anything jumped for normal use, as the pressure switches are vital for preventing damage to your compressor.
If your fuse is good... the next voltage check I would do is your low pressure switch. You should read 12 volts on one of the terminals in the plug. This will give you an idea as to which direction to continue in the wiring to find your problem. If you read 12volts there, and jumping the plug doesn't engage the compressor, do a continuity check across the switch. With pressure in the lines (above 17-22 psig) you should read continuity between the plug terminals. If you do not, replace the switch.
I hope I was of a little help, if you need me to go into more detail about a certain point, feel free to ask. Thank you for the question, and good luck in everything
