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: 6/25/2008 Subject: auto ac
Question I have a 1998 Toyita Avalon. When I turn the ac on the clutch on the compressor does not engage. Any ideas on what the problem might be?
Answer Tom,
You have two pressure safety switches inside your system. One for the high pressure and one for the low pressure. The low pressure cuts off the compressor when the pressure drops below a certain point, typically between 16 and 26 psig) At idle your compressor is not turning as fast therefore your low side pressure switch stays engaged. The faster the engine revs, the faster the compressor turns therefore it is going to pull a lower pressure on your low side, and may be disengaging your switch. It is very possible that your refrigerant charge may be low due to a small leak. As the engine develops higher rpms, it pulls the low side pressure below the opening point and shuts down your compressor. With your pressure readings I can expand more, but from the sound of it this is the most likey cause. A low refrigerant charge. The easiest way to check for this is as follows...
Locate your low pressure switch. It is typically located on your accumulator ( an aluminim canister, roughly the girth of a soda can, with two lines coming out of the top of it.) Disconnect the wiring harness plug from the switch, and with an insulated wire, jump the connectors inside the harness. With your switch in the run position and your A/C on, your clutch should engage. If it doesn't let me know in a follow-up and I will work you through the rest of the schematics. If it does engage, then I would check your pressures, because you more than likely have a leak in your system.
After you jump it, if it doesn't engage the compressor, take a voltmeter and with the switch jumped, check your reading at the compressor hot wire. You should have 12 volts. If you have 12 volts and it is not engaging, that means you have a bad ground, and it may just need to have the connection cleaned.
The A/C world is controlled by pressures and you would be amazed at the different things they can tell a technician.
Thanks for your question and I await your reply with pressures.
