After a very cold winter, it finally got hot enough today to warrant use of the air conditioning in my STi. I pressed the button, the green light came on, but no cold air. I cycled the button on and off and still nothing. Then I noticed that the engine didn't bog for a moment after the button was pressed like it normally does on most vehicles. I opened the hood and noticed the compressor clutch hadn't turned on. I opened the fuse box in the engine compartment and swapped the relays for the A/C and the radiator fans, since the relays were the same and the radiator fans were operating normally. Still, the A/C clutch wouldn't kick on. I went back to the fuses near the driver side (right side here, maybe the fuse box is elsewhere on US models) and checked the A/C fuse which was still fine. I pulled it and the interior fans turned off. If its not the switch, fuse or relay, what could cause the compressor clutch to not turn on? Maybe I missed something in the chain?

I also disconnected the plug leading to the clutch and took readings with a multimeter. It read 14.5VDC with the switch on or off. If you have any info, please help! The days are getting hotter and the only solution I can see is roll down the windows and drive as fast as I can to keep cool! Thanks.

FYI, its a 98 STi with the EJ20K motor, but I think Subaru's A/C may be almost the same across the board.

 

The system probably has a leak and the refrigerant has leaked out. Once the charge gets below a certain level there is a low pressure cutout that activates to protect the compressor.
You need to take the car to a shop that does A/C work and have them put gauges on it to check the charge level, then recharge it if necessary and find and fix any leaks.

 

Exactly what happened. I read some of the stuff on Ravensblade about the workings of the Subaru A/C system and then went out to buy refrigerant. 3 cans and $18 later, and now the compressor kicks on as advertised. I have been checking the lines for leaks, but nothing yet. Thanks!

 

You should still have a shop check it. You may have got it working by sticking a few cans in there, but you have no idea if the pressures are correct. Also there is probably still a leak and eventually it will all leak out again. It's not normal for the system to lose refrigerant.