Driver's side heat changes to cold

2008 CADILLAC DEVILLE DTS
80,000 MILES
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RALPH LASLEY
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After about fifteen minutes of driving, all outlets on the left side switch to unheated outside air regardless of temperature setting. It will switch back to warm air for a few minutes after restarting the engine.
For both sides, a setting of 78 gets to about 70. The A/C works okay.
The outside temperature display usually reads much warmer than it is and sometimes rises high then plummets when A/C on. Outside sensor replaced but no change.
Do I need a new main control or just a left blend actuator (and how is that accessed)?
Feb 23, 2019 at 4:51 PM
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ASEMASTER6371
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Good evening,

There is a temperature sensor inside the car which sends a signal to the controller.

The actuator is working as you have cold and heat moving as it should.

I would check the inside temperature sensor.

Roy

Feb 23, 2019 at 5:32 PM
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RALPH LASLEY
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That schematic is of the 2000-5 Deville (my previous car), but I'll try your diagnosis. I know where the sensor is as I vacuumed the lint out of it recently. It's a $25.00 part (now ordered) vs. $250.00 for the controller. Thanks.
Feb 25, 2019 at 5:51 AM
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ASEMASTER6371
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Keep me updated.

Roy
Feb 25, 2019 at 5:53 AM
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RALPH LASLEY
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No luck. The heat turned cold after 23 minutes. Looks like it must be the controller, since the actuator moves, and I assume it could not on its own.
Mar 19, 2019 at 3:35 PM
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ASEMASTER6371
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Did the actuator go back to the cold position when it turned cold?

Roy
Mar 19, 2019 at 3:50 PM