Heater issues

[Polaris]

I own a 99 STS.

While the driver side heater works the passenger side does not. Of course it occurs at the coldest time of the year.

For a while nothing worked no heat no fan. I opened the access panel to the fan from the passenger side a the driver side started blowing hot air. All of the fuses are good. So is this a connector issue?

Any suggestions?

[Cadillac Jim]

This sounds like a mixer door problem. I would check the vacuum to the HVAC programmer and read the OBD codes.

One way to check the vacuum through the HVAC is to put the car in Park with the engine running, press the emergency brake, then see if the brake releases when you put the car in Reverse or Drive. If so, vacuum is getting through the HVAC programmer to the emergency brake release.

[KHE]

The mixer doors are controlled by electric actuators. Run the diagnostic codes and post them - it is likely one of the actuators is not moving to the position commanded by the ACM programmer. The codes in particular to watch for will have the ACM prefix.

[Polaris]

Thank you both , I will check it out. By the way, the parking brake does not release. I have a trail to follow.

[Cadillac Jim]

Start with finding the vacuum hose where it comes through the firewall and connects to the A/C programmer.

[JimD]

Start with finding the vacuum hose where it comes through the firewall and connects to the A/C programmer.

Write this down 100 times, Jim.

There is nothing vacuum operated in the cabin of 1998+ Sevilles.

There is nothing vacuum operated in the cabin of 2000+ Devilles.

[barczy01]

Look for a little yellow handle on the Pbrake assembly with a flashlight, its hidden.

Check the basics, is the cooling system full of coolant and reaching operation temp?

Are both of the heater core hoses hot?

[Cadillac Jim]

Start with finding the vacuum hose where it comes through the firewall and connects to the A/C programmer.

Write this down 100 times, Jim.

There is nothing vacuum operated in the cabin of 1998+ Sevilles.

There is nothing vacuum operated in the cabin of 2000+ Devilles.

You have a nice day too, JimD!

[Cadillac Jim]

The 2002 FSM is the closest model year to 1999 that I have available but it should be correct.

 

There are independent air temperature doors on the left side and the right side, as well as sun load sensors, etc.  Repair is very different for different problems and is unwaveringly not simple, and I would strongly suggest that you get the OBD codes and get a firm diagnosis before taking anything apart.  Check the link in my signature block for instructions on running your OBD codes.  Be sure and mark which ones are CURRENT.

 

It does sound more like an actuator.  Diagram from 2002 FSM:

 

 

The diagram is nice but get the OBD codes to begin the process. That will likely help with the emergency brake release issue too.