Hello, I have browsed the forums for a long time but finally made an account to see if anyone has any idea what my issue could be. Since buying my FC, my AC has never worked, though it appears at some point it was upgraded to use a newer refrigerant. I looked at all my AC components, relays, wiring, compressor, and everything seems good. If I jump the compressor to the positive battery terminal it engages, and will blow cold air in the car, but wont engage with the AC button. So I took it to a shop, they said might be electrical issue but recommended another shop, and the second shop said it appears the ECU may be blocking the signal to engage the clutch, but he 'isn't a wire chaser'. I tried to skim thru the pages of the forums to find something but haven't seen the same issue yet. I will add, neither shop hooked the system up to their fancy AC machine to check refrigerant level, or add or subtract from it. Blower motor works, just compressor doesn't engage with the button. New Relay installed already.

If anyone has experienced this issue, or knows of a pre-existing discussion and would link it to me, any help would be much appreciated.

 

Sucks to have AC problems in the middle of July, but hopefully we can help you get it going.

A multimeter is going to get you pretty much all the answers you need. The factory service manual, found at Foxed.ca has a thorough and complete section for AC diagnostics and troubleshooting. It's worth downloading and reading through.

In continuity mode, the first thing I would check is the pressure switch, located near the drier up front. If there is continuity on that, you have adequate pressure. If not, you have low refrigerant. Keep in mind that low refrigerant can still cool things, but it doesn't cool as well, or circulate oil for the compressor very well. If there is continuity through the pressure switch, we have something else going on.

The ECU does play a role in engaging the AC clutch. It does this by controlling a relay that supplies battery voltage to the clutch. The ecu controls the relay by internally grounding the coil side of the relay. If you can ground the coil side of the relay and cycle it, then your clutch should engage as well. If not, might be a dead relay.

The ECU receives a signal to engage the clutch with 3 switches. There is the button on the dash, the thermoswitch inside the dash to see how cool things are, and the pressure switch. With the AC button pressed, you should be able to measure a path to ground from one of the terminals at the refrigerant pressure switch up front. The other should have positive voltage with the key in RUN. If you don't see ground or positive voltage, then you have more wires to chase. The ECU would be the last resort.

The most likely reason they wont touch it is that the system is intended for R12 and they don't service R12. Shops around here have refused to touch my AC system, so I had to go the DIY route and do the R152 conversion that is described on here in another excellent thread