Help with a ventilation issue on a 81

[Ciro A.]

My 81's ventilation system is only capable of blowing air from the foot well outlets. If I select the defroster, or upper vents nothing happens. Is this a selector panel issue? ie. just buy a new one or can it be diagnosed and repaired easily? I'm trying to sell the car and would like the ventilation system to operate properly. Any hints or advice?
Thanks guys

[Tom B.]

Re: Help with a ventilation issue on a 81

Check your vacuum hoses to the diaphragms that control the heater/defroster doors. They may be old and cracked or off completely. Also could be a bad diaphragm.

Tom

[Ciro A.]

Re: Help with a ventilation issue on a 81

Tom,

Wheres the diaphram located?

[Ciro A.]

Re: Help with a ventilation issue on a 81

I have the side panels off, and the glove-box out..all vacum lines are connected to the selector panel...the diafragm I'm suppossed to be checking is not easily viewed. Is it on the engine side of the fire-wall or inside?? any help appreciated.

[Tom B.]

Re: Help with a ventilation issue on a 81

First off with the engine running do you have a massive vacuum leak out of the control unit on the console? Try it in all positions. If not I'll see if I can point you in the right direction. We will refer to the vacuum diaphragms as actuators from now on.

As you have seen the vacuum hose system is a harness that all comes from the connector on the a/c-heater control selector valve on the console. Each hose has a color stripe to identify it. A simple fix would be to find a hose that is bent too tightly and collapsed. That's unlikely if it is still all factory installed hoses.

Your problem is the diverter door isn't opening. It could be the actuator, something blocking the diverter door from moving, like a mouse nest, or no vacuum to the actuator. These doors have a spring on them that pulls them closed. The actuator pulls them open. There are 2 doors that control the air flow to the heater def outlets and the a/c outlets. Both of these actuators should be visible on the outside of the heater box under the dash. Probably not easy to see or get your hands on either.

One door contols air flow to the a/c outlets and the other controls air flow to the upper def outlets and the lower heater outlets. This door also has a bi level position that splits the airflow. Both of these doors working together give you all of the combinations of airflow that you can select from the console control.

Does your a/c blow through the a/c outlets? if so we can eliminate any problem with that actuator and go to the other one. This will also tell us if there is actually vacuum to the control unit. If not then the problem may be in the control or the vacuum supply to the control.

Since you are getting airflow to the lower outlets we know that the door is closed and not getting vacuum to pull it open. If you don't get any airflow through the a/c outlets also then I suspect there is a problem with the line to the source or a problem with the control unit. On the control unit vacuum plug one of the hose lines is all black. That one goes to the source under the hood. Unplug the hose harness connector from the control unit and check for vacuum from the all black hose (engine running). It should be a full time vacuum source. If not follow it to the engine to find out why.

If you have vacuum at the source hose then we need to look at the actuators. Here is where it can get simple or hard. Simple because you may not have to torture yourself by trying to get under the dash. You will need one of those hand operated vacuum pumps. If you don't have one you can get one from the free tool loan deal at Auto Zone or get one at a tool rental place.

What we want to do is draw a vacuum on the hose that goes to the actuator for the diverter door. The hoses are glued to the control unit plug so you may have to cut them off and then re-install them after the test. There are 2 hoses we are concerned with; blue stripe and tan or orange stripe. One diagram says tan the other says orange. Also one diagram shows the blue stripe to the heater/def actuator and the orange or tan to the a/c and the other diagram shows them the other way around. Anyway, when you pump a vacuum on the line you will know if there is a leak if it won't hold the vacuum. Also you will be able to hear the door open and then snap shut when you release the vacuum. If this happens on both the blue strip and the orange or tan hose you know that the doors are functioning. That leaves the control unit.

I don't know what the availability of these are but if you have vacuum to the control unit and the doors are opening and holding vacuum then there is no other choice. I hope this helps you find the problem.

Tom