AboutDavid Hill Expertise I can answer questions concerning automotive air conditioning systems, residential air conditioning systems and electrical repair questions.
Experience I have 16 years of experience in the automotive air conditioning arena and am currently an instructor for H.V.A.C.
Education/Credentials I am certified through as a universal technician under sections 608 and 609 of the C.A.A.
Expert: David Hill Date: 6/26/2008 Subject: A/C wont turn on
Question I have a 1987 Cadillac Deville. The SERVICE AIR CONDITIONING light on the dash comes on when you try to turn A/C on. Mechanic says A/C is fully charged and problem is with the A/C Control Head in the dash. Replaced the Head and the A/C Module with two good used ones and still doesn't come on. Any suggestions would be appreciated. Thanks.
Answer Tracy,
Inside your AC system, there are two safety switches to protect your system. One is your low pressure switch.
If the AC tech said that your refrigerant charge was good, I want you to locate your low pressure switch. It is usually located on your accumulator (an aluminum canister, roughly the girth of a soda can with two hard lines coming from the top) If it is not located there, I need you to trace your low side line from your compressor until you come to it.
When you find it, disconnect it. With the A/C on and the engine in the run position...
With an insulated wire, jump the connectors in the wiring harness, this should engage your clutch. If it doesn't...
Check the wires on the sewitch with a voltmeter, you should have 12 volts at one. If you do, put your jumper wire back in the wiring harness and check the voltage at your clutch wire on the compressor. If you have 12 volts there, you may have a bad ground, and it just needs to have the connection cleaned.
If you read 12 Volts at the low pressure switch, jump it, and do not read 12 volts at the compressor, you have a break in the wire somewhere between the switch and the coompressor clutch. Or your low pressure switch has gone bad. To check for a break in the wire, Un jump the switch, place your multimeter on continuity or resistance, place one multimeter probe on the switch harness with the wire going to the clutch, and the other probe on the compressor hot wire. You should read resistance, or hear a beep. If you read resistance or hear a beep, replace your low pressure switch.
Now step back, if you did not read 12 volts coming into the low pressure switch, the next step is your compressor relay. Check that to see if it is energizing. If you need me to walk you through that, do a follow-up, and I will be more than happy to.
I hope I was of a little help, and didn't get too confusing. Thank you for the question and good luck.
Fact of the matter is, many mechanics have little to no idea of how the automotive AC system works, and will many times just give you an answer to sound like they do. It's a terrible fact but true.
