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92' Sc400 Blows Cold Air In My Heater


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If you search the older section of the SC forum and look for "heater control valve" or "air mix servo motor" you should get some hits. These are the two causes I know of for cold air blowing. (This is from experience) The first thing (and easiest) to check is the heater control valve which is located in the engine bay, on the firewall, passenger side. It is near the top of the engine bay and very easy to access. There is two vacuum lines going into the valve. You can try swapping the vacumm lines and see if it works. If it does, you can leave it this way until you can get a new or used valve. If this does'nt work, you can perform a self diagnostic using the built in diagnostic of the climate control system. While turning the car key from off to the start position, simultaneously hold the Temperature control knob and the recirculate button. The system will go into self diagnostic. It will automatically index through the various system settings and flash a code if there is a problem. Mine came up with a code 41, which means there was a problem with the air mix servo motor. If you do the test in low light, you may get a code 21, this is the solar sensor circuit and is nothing to worry about. Try the tests and let us know.

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