You are here:

Cadillac Repair/Heating cooling distribution


QUESTION: Recently only 1/2 (driver side) of the windshield will defrost.  Also heat will only come from the passenger side vents.  Driver side remains cold although passenger gets warm.  Plenty of heat so it is not the heater core and AC works fine.  Could it be the distribution valve under the dash on the passenger side?  Had also been making an odd squeaking noise from that area too although it was hard to tell exactly where it came from.  Either that or one of the diverter valves?

Thanks for any input


ANSWER: Hello Greg,

Make, model, year would help. The A/C is a separate system than heat. As for the distribution and temp on the other side, that sounds like a mode door or two not functioning, usually created by a vacuum problem. Most mode doors are controlled by vacuum. Door(s) could be binding or vacuum line pinched.

You would hav to get under the dash, find the mode doors and apply a vacuum pump to them o see which ones are functioning. Cut off vacuum or a binding door would explain the noise you are hearing as well.

---------- FOLLOW-UP ----------

QUESTION: Thanks Rob,

Sorry about not identifying the car!  It is a 1997 Cadillac Eldorado ETC.  Pulled the distribution valve at the passenger side and it seems fine.  Air flow to various places seems OK and it is just the heating that seems not to get to the right place.  Is there a specific diverter that controls hot/cold?


As I stated before, you will need to get up under the dash and use a hand held vacuum pump on the mode door giving you your noise and lack of warm air in that location.
The only diverter I am aware of is at the control. Everything else is controlled by vacuum lines going to specific doors. A pinched line under the dash could also give you an issue.

Good luck.

Cadillac Repair

All Answers

Answers by Expert:

Ask Experts


Rob Painter


Alarm system questions cannot be answered on this forum. These systems are not what I can answer. Without being physically at the vehicle and not knowing what kind of electrical service has been done on the vehicle, there is no possible way to give an accurate answer over the internet. My expertise is in Ignition/key based anti-theft systems. These issues include GM VATS (resistor chip in key blade) PASSLOCK (MRD)-ignition lock rotation based, no special ignition key and the PKIII Transponder (computer chip in key) systems. These systems are not alarm based and are integral with the starting of the engine. This is why I cannot diagnose alarm problems without physically looking at the vehicle: Alarm systems are a completely different annimal than ignition key/lock based anti-theft system. Many alarm questions come from vehicles 10 years old, and since older, many hands that had been involved over the years.I am an expert in all GM factory (ignition/key based)systems. Alarm system questions pose to many situations beyond my knowledge as to what has been done to the vehicle over the years. Some guy may have actually wired the stereo into the alarm system. Who knows? Over my past 30 years in vehicle wiring repair, I have seen unbelievable wiring disaters done by guys that consider themselves "mechanics." I have seen stereos and alarms intalled using surgical tape. I have seen modules burn up, un-fused circuits, wiring jambed between the doors and even lamp cord used for a starter kill. To answer alarm questions over the internet without examining the vehicle is like asking; What does it take to remove a dent?


Education/Credentials-ASE certified. 11 years with a GM dealer and 17 years with a repair facility dealing with only the repair of theft recovered vehicles.

©2016 All rights reserved.