I'm experiencing a problem with my A/C compressor. It's never engaging when I hit the button to turn it on. I stopped at a car shop yesterday and they told me it's charged with Freon and that they think it is an electrical problem.
Well, since I'm an electrician not a mechanic I figured I might be able to troubleshoot the problem. All fuses seemed to be ok by sight and checked good with my meter. The larger relay in the electrical box had continuity between two diagonal poles.
Sorry for the length of the question, just trying to be informative. Thanks a lot, and I forgot to tell you it's a 2000 model Chevrolet Silverado 1500 with the 5.3-liter V8.
Trust me, there's never too much information in a reader's question, unless there's 12 questions in a reader's question. Note: a U.S. built 2000 model year truck uses R134a refrigerant, not Freon (R12).
OK, you're on the right track. If the system is fully charged (pressure correct), but the A/C compressor clutch does not engage, the fault is electrical. You're experience as an electrician directed you to first check the basics (fuses), and now it's time to trace the circuit and determine what we lost (power or ground) and where we lost it.
If you test for 12 volts at the A/C relay terminals (engine compartment fuse block, left side fender) you should detect voltage at two of the four terminals which are marked (30) and (86). That's power from the A/C fuse and Ignition fuse E, respectively. Now take a jumper wire and connect it between terminal (30) and terminal (87). With the ignition on this should send the 12 volts from the A/C fuse directly to the A/C compressor. You'll hear and see the compressor clutch engage if everything on that side of the circuit is good.
If not, there's a break in the power wire form the relay to the clutch, a break in the clutch ground circuit, or the clutch itself is no good. If it works fine, it's going to require more advanced testing on the control side of the circuit. The relay could be bad, or it's not getting the needed activation ground at terminal (85) which comes from the Powertrain Control Module.
The powertrain control module needs to receive a bunch of correct data from switches (three pressure switches under the hood), sensors and the HVAC control module before it will engage the A/C compressor. The best diagnostic route for a technician would be to check all these inputs with a scan tool before taking the next step.