Hey fellow motorists! Learned something new today that I thought I'd pass along.

After reinstalling my cylinder head (post valve job for a warped head/failed head gasket), I noticed my AC temp was a little high (63 degrees at the register discharge). There are many things that could cause this problem so my first step was to connect my AC gauges and check the low and high-side pressures. Readings indicated I had a problem with the expansion valve, so I changed it out, pumped down the system, and re-serviced. The discharge air temp at the registers remained unchanged even thought I was seeing the correct pressures based on ambient air temps.

So, I pulled out my Foxwell GT80 mini, and my fiber optic scope (use the vent just to the right of the speedo). In full heat mode, I could see the heater core, and the scanner showed I was at 100%.


When I selected full cold, the temp control door servomotor showed 17%; I was expecting to see 0%. Notice how you can still see the heater core with the door in the (mostly closed) position.

So, I took the car for a drive and pulled up the evaporator temperature sensor in the GT80. It was handy that MINI engineers put the sensor on the evaporator. I also installed a thermometer in one of the registers. When I started the drive, the register temp was 58 deg F and the evaporator temp quickly dropped to 45 deg F. During the drive, the register temp climbed to 63, but the evaporator temp was a rock solid 45. So I had my proof that air from the heater core was passing by the (mostly closed) temp control door and mixing with the air from the evaporator. The problem is probably with the temp control servomotor, but I won't know that for sure until I pull it apart and make sure the door isn't binding or obstructed.

So, if you are experiencing higher than normal AC temps, make sure you eliminate all possible causes before you break any refrigerant lines.

Cheers!

K