Compressor clutch not engaging

[Th4tGuy]

Hey, so I swapped my ac system to r134 an about 2 years ago and it has been working like a dream but I tried to use it at the beginning of spring and it didn’t work. Figured it had just lost its charge so I got it recharged but it only lost half and even once recharged it wasn’t blowing cold. Figured out that the compressor clutch wasn’t engaging and the plug for it wasn’t getting signal. I have a late model style so just 1 pressure sensor for hi/low and I checked that and it seems to be working and getting power but I’m not entirely sure what is on and off but it has continuity when I tested it with the car off. The relay (K7) seems to be working and I even swapped it around and nothing changed. The relay is getting power and the ac button in the car seems to be working because it turns on the electric fan and the relay clicks even though the blue light for it doesn’t turn on. I followed the wire for the clutch all the way back to the fuse box and nothing is frayed or broken. Anyone have any ideas or experience with this and how to fix it?

[MrBurgundy]

When I diagnose a/c I'll start with making sure the system is charged, which you've done already. After that I'll work backwards from the compressor to the button.

You should jump the clutch to make sure the clutch is still working, then test for signal at the plug, You should have power when the button is pressed and the ground is supplied by the pressure switch.

After testing the clutch and if it works, you're going to be missing either the hot or ground signal. I forget off the top of my head how its wired in an e30, but usually the hot will come from the button, to the fuse box to possibly a relay before going to the clutch itself

and the ground will come from the pressure sensor

Should be an easy find. Let me know what you find

[tomstin]

A few thoughts. First, the vent sliders have to be in a specific position for power to go toward the compressor. The slider contacts can be dirty. When I had my dash apart I bypassed that switch. Next inline is a sensor in the evaporator that prevents freezing of the evaporator. They can fail. The sensor is located behind the air vents up above the gas pedal. A royal pain in the butt to check.

So, power in and out of the AC snowflake button, through the sliders to the evaporator then on to the dryer and compressor.

Anytime you are working with these vintage AC systems, a worthwhile investment is "Just needs a Recharge" by Rob Siegel. Good Luck!

[Th4tGuy]

When I diagnose a/c I'll start with making sure the system is charged, which you've done already. After that I'll work backwards from the compressor to the button.

You should jump the clutch to make sure the clutch is still working, then test for signal at the plug, You should have power when the button is pressed and the ground is supplied by the pressure switch.

After testing the clutch and if it works, you're going to be missing either the hot or ground signal. I forget off the top of my head how its wired in an e30, but usually the hot will come from the button, to the fuse box to possibly a relay before going to the clutch itself

and the ground will come from the pressure sensor

Should be an easy find. Let me know what you find

Sorry for taking so long to reply. My car is a 318is 91 so I don’t think that it has the switch in the sliders. After going trough all the relays and switches i looked on the 3rd wiring diagram i had found and it said fuse 19 which is the fuse for the power mirrors. I had already checked Fuse 20 and relay K7 but not 19. Turns out it was not there (idk why it wouldn't be) but i put a 7.5 in it and it worked. So lesson is check your wiring diagrams even if you think you checked everything. there are also other diagrams so don't fully rely on this but here is where i found it on page 6452-1: http://wedophones.com/Manuals/BMW/19...g%20Manual.pdf