91 Electronic Temp Control Question
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Joined: Jan 2005
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91 Electronic Temp Control Question
Recently, the only way to get any heat is for me to turn the temp all the way up to 90 degrees. Anything less than that blows out cold. Can anyone lend advice to what's wrong? The temp unit is not throwing any codes (pushing the fan arrow up and down at the same time). Thank you!
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
At some point, GM programmed Electronic Controls to only send heat when the Coolant Temp Sensor Signal was something above 100 degrees, so you might want to make sure it's warmed up. Otherwise, at any Auto Temp other than 60 or 90 the Programmer is designed to position the Temp Door based on the input from the Inside and Outside Temp Thermistors. Therefore, if it's toasty inside, you may only get cooling, even it's freezing outside, at any temp setting other than 90. That's not to say there isn't something screwy with the Programmer or one of the Sensors. The best place to start is to look at the numbers in the Data Stream (not the Fault Codes). Go here to access it: https://www.corvetteforum.com/techti...=193&TopicID=2 - post what you get. It may tell us something; particularly the input from the Inside Sensor - Range is 130 (Hot) to 230 (Cold).
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
You're not getting into the Data Stream - go over the Tech Tip again.
You might also try clearing memory or any glitches - disconnect and reconnect the battery. When you restart, the Temp Door will cycle so that the Programmer can learn it's position. While it does this, nothing else will work - Blower Motor, compressor; but once completed, everything should return to normal - or at least be back to where it was. For what it's worth, there was a Service Bulletin issued for the '90 recommending this procedure with the cause linked to inserting the Radio or Courtesy Fuse with the ignition on. Then, a '91 Bulletin was issued tracing the problem to a bum Programmer - VINs: M5100001 through M5101083 - so if you have one of these VINs, you may need a new Programmer.
You might also try clearing memory or any glitches - disconnect and reconnect the battery. When you restart, the Temp Door will cycle so that the Programmer can learn it's position. While it does this, nothing else will work - Blower Motor, compressor; but once completed, everything should return to normal - or at least be back to where it was. For what it's worth, there was a Service Bulletin issued for the '90 recommending this procedure with the cause linked to inserting the Radio or Courtesy Fuse with the ignition on. Then, a '91 Bulletin was issued tracing the problem to a bum Programmer - VINs: M5100001 through M5101083 - so if you have one of these VINs, you may need a new Programmer.
