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Old 06-29-2008, 01:17 AM   #1
Scooby Specialist
Member#: 123574
Join Date: Aug 2006
Chapter/Region: MWSOC
Location: Lisle, IL
2005 stuck-in-garage

Default HVAC Troubles

Some time last week my HVAC system in my '05 STi started behaving strangely.

I noticed that when I started the car, the outside temperature gauge would read a ridiculously high temperature, like 122 degrees. Sometimes it will drop to a more realistic temperature later, sometimes not. Then I realized that the AC was no longer blowing cold when set to "Auto." I played with the dials, and the only way I can get it to blow cold (and it's ice cold) is by turning the temperature dial all the way counterclockwise (below 65 degrees.) Combining this with the manual setting for fan speed, I can regulate the temperature comfortably... But it's annoying!

I'm inclined to think that the malfunctioning outside temperature gauge is in some way involved in the HVAC system no longer working properly. Does anyone know how I can troubleshoot this?
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Old 06-30-2008, 01:51 AM   #2
Scooby Specialist
Member#: 146819
Join Date: Apr 2007
Chapter/Region: NESIC
Location: Boston / Ipswich, MA
'02 WRB VF-39'd WRX
W/06 STi Drivetrain swap


well the HVAC unit does use input from the outside temperature sensor so it could be the culprit.

Something to keep in mind while trying to figure out this problem is how this system functions. The outside temperature sensor is not as simple as just sending sensor temps, the computer doesnt use input from this sensor if the car was on in the last hour, instead it uses the last valid reading it got. When the vehicle speed very slow (I believe it was below 1 MPH) the computer continues to use the last reading from before you slowed down. this may or may not play a role, just something to think about as far as noticing when it reads high.

Get a hold of a diagram and start tracing the wires looking for trouble. I can send you an E-Mail with the diagram for this system if you PM me your email.
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