My wife has a 2012 suburban. We noticed this summer the rear AC would blow slightly cold air and room temp air back and forth a few seconds at a time. Now this winter we are noticing that the heat is doing the same, slightly warm air to cold room temp air back and forth. Any ideas before I hit the dealer ??

 

Update, I took the trim pieces off the rear heater to see what was going on. When the rear heater is on, I notice that the rear dampener actuators are moving back and forth on there own. Letting cold air mix into the system. This is telling me it's a control issue. Next step is to find what controls those actuators, I'm guessing it on the console controls.

 

Is that the climate control adjusting the temperature output? Set the temp all the way to coldest or hottest and see if it remains stable.

 

You will need a bi-directional scanner to actuate the doors. Scanner will also show what the control panel is telling the doors to do.

 

With the setting all the way to hot or cold they fluctuate back and forth. Where could I find this scanner?

 

Most reputable repair shops will have one . The cheapo's at the parts stores do not usually have the bi-directional capability.

 

 

Check for codes with the scanner. Should be setting codes.