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1999 cadillac STS
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13 Posts
Discussion Starter #1
My 1999 Cadillac STS dual climate control is having issues. The driver's side is blowing warm air, but passenger's side is blowing cold air. Same as the front defrost air, driver's side blowing warm air but passenger's side is cold air. Anyone know what the issue is??
 

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2002.5 F55 CORSA STS, 2014 Explorer XLT FWD
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68,470 Posts
Either a slightly undercharged r-134a load or one of the HVAC stack blend doors or actuators has failed. Several recent threads here and in Deville on this, as well as down in Cadillac Tech Tips.

Pull any diagnostic codes from your car's built-in code scanner/reader. The HVAC actuators are monitored for function/position. Study the proper year group/model for your car in the sticky post ^^^ "How to pull codes".
 

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White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
I assume this is in the heat (not A/C) mode? Or are you way down south and still using A/C?
 

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1999 cadillac STS
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13 Posts
Discussion Starter #4
No, I'm in Illinois too. Therefore, my windows keep fogging during this winter climate.
 

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72,92,02 Eldorado
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185 Posts
If it's your blend or mode door, stay tuned.
There is a good write up on the mode door in the Deville section.
I have read hundreds of posts on the subject and have yet to find any definitive answer for the blend door. Most have given up and installed a manual actuator like a wire or something. I will get mine working now that I have the motor running correctly.
Replacing the blend actuator and disconnecting the battery, discharging all caps onboard, did not do the trick. I have a feeling it has something to do with the feedback line indicating that the blend door is closed or a passenger side temp sensor if there is one.
I'll start a thread on the subject once I start testing in a week or so.
I'm in Texas so A/C is fine with me most of the time:D. And I can always use the off button or close the passenger side vents.
Taz
 

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Super Moderator
White Diamond '03 DHS (with DTS floor shift)
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86,785 Posts
Follow Sub's advice in post #2 and pull the DTCs. If you have a bad actuator it will set a code. If not, you might try flushing the heater core. You might have sealant tab residue settled in the bottom, stratifying the air flow through it.
 
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