wagonman76

I am having this problem which has me stumped. When the temperature control is set to hot, all airflow modes work just fine. However when it is set to cold, all the airflow comes out the defroster vents, regardless of mode setting. The amout of airflow coming from the defroster vents is proportional to how far the lever is set towards cold.

All three vacuum actuators for the airflow modes work properly, in hot or cold. The temperature control is a simple cable control. Also, the airflow problem happens as quickly as I can move the lever, which is much faster than the several seconds it takes for the vacuum actuators to operate. Its like whatever happens is independent of the airflow modes. Like there is some mechanical door that, when set to cold, is directing the airflow out the defroster vents instead of through the rest of the system.

I wonder if anyone has ever been inside the HVAC unit on one of these cars? Is there anything internally that may be broken or disconnected?

Blue Bowtie

It almost has to be something in the temperature control or dampers creating a vacuum loss to the rest of the HVAC system.

If you have access to a factory service manual (many dealerships will allow you to look at their manuals and even copy pages - If you're patient and allow them to take care of paying customers first) you might find something like this to assist you:

wagonman76

Thanks for the reply Blue Bowtie.

I have a service manual from an 88 Century which has the same system and control head. I have looked through this manual and found the corresponding diagram, as well as others. All the vacuum modes work properly. Ive run the engine and played with the modes for a good half hour and watched and listened to the actuators. But its like when I move the mechanical lever to cold, the air is being directed straight out the defroster vents by something mechanical. If I throw the lever one way, the air goes properly (hot) or out the defroster (cold) immediately, within a split second. If it was something additional that was vacuum controlled, it seems like it would take a few seconds, like the vacuum actuators take.

Im wondering if this manual cable controls more than one flap through a linkage of some sort? Sort of like how a throttle cable also controls the cruise and TV cables. There is nothing more than a simple connection externally, but I wonder if one was to remove the dash and the HVAC unit and disassemble it, if there was something like this inside. Before I was to go and possibly tear out the dash for nothing, I was wondering if anyone has been inside the HVAC unit.