chekbaka

O K I have a quick question. I have a 91 Camaro 305 engine TPI automatic. The upper switch of the AC/heater control module (or whatever its called ) does not work properly. As it slides from left to right, you know from the three different settings for the AC to the ventilator, heater and defogger, nothing happens. Air only comes out of the defogger vents under the windshield. Also I am not getting any heat but that is another problem that I think I can fix after some of the suggestions that many of you have given me.
What I need to know is how does this upper switch (or whatever it is called) works. In the past whenever it was pushed from left to right it initially turned on the AC and then either switched the air from the vents on the dash, to the ones on the floors and the ones on the windshield as you all know. Now nothing happens. The AC doesn't turn on at all and the vents don't change. The blower is working fine as I can hear it and feel the air coming from under the windshield vents at full blast. I just need to know how does this system work. As the switch is moved from the left to the right is it just moving a cable opening or closing vent doors or does it use another type of mechanism?. I have read on several manuals about actuators and the need of vacuum for this mechanism to work properly opening the vent doors. Is this the setup on a 91 tpi camaro?. If so, where are the vacuum hoses, or vacuum motor etc. If its just cable driven then I guess I can figure it out on my own. I have taken my stereo out and checked that the lower control cable the one allowing cool or hot air to pass is still attached. I haven't taken the control module yet to check the upper switch but I will do so as soon as it stops snowing over here in Utah. I just need to know the following things:

- Are the vents cable controlled or actuator controlled and what can I do to let air come from either the vents on the dash, floor or defogger(this is the only one working)

- Why my AC does not start at all. I think my refrigerant is empty and the whole system hasn't been cooling for a couple of years now, but shouldn't sliding the switch to the right start the compressor anyway?.

Any help will be greatly appreciated, Thanks!

bulletboy29

It's vacuum controlled on my '87. There should be a vacuum line somewhere on the passenger side of the engine compartment if it is like mine.

CEP89

The vents use vacuum to operate. There is a hard plastic line that gets brittle when old (it breaks when you barly touch it). it goes to the heater control valve under the hood from the HVAC control head. There is also an other hard plastic line going from the HVAC control head to the intake manifold to supply vacuum.
Your A/C compressor has a saftey cutout that won't let it run if your system is empty.

thunderstick

your "vents" are actuator controlled. the cable on the hot/cold slider does nothing but open the heater door, basically. the air comes out the defrost vents only because of "default". if all other systems fail to work, it comes out there. a couple of probable causes are (1) one that's already been mentioned - the vacuum line in the engine compartment, and (2) the vacuum line on the back of the selector switch on the a/c cont head. that is a cluster type connector with about 5 vacuum lines on it, one of them being the vacuum supply line. many times the seal around those tubes gets weak, even tho you can't really tell. you have a couple of options to fix it. one is that you take that cluster connector off and apply vaseline with a q-tip to the inside of each of those 5 tubes and reinstall it, or if that doesn't work, you can cut each one off individually and reattach, securing with a small zippy-tie on each one, which is what i've had to do, or (3) worst case scenario is that you have to replace that whole vacuum tube harness, but i doubt that and you wouldn't want to do it anyways. i can't vouch for the vaseline trick, just heard about it. but it is the easiest to do. if it don't work, i'd go for the separating of the tubes. that works, or at least worked for me. a word of advice, remove your stereo cuz it'll make it so much easier, and put a rag or towel over the tunnel area under the cont head cuz if you drop one of those washer thingies, it won't get lost on you... good luck.

chekbaka

You guys are so awesome!. Thanks for all the details. I will do as suggested. I am a little bit worried about getting the control head out. I took my stereo out trying to troubleshoot the problem about a week ago and it seems ti be pretty held up in there by the cables atached to it and stuff. I am afraid of breaking or not being able to re-atach the cables properly but I know I will figure it out. Your details helped a lot.

Now I have another question which I posted on this board not too long ago. In addition to the air coming out only from the defogger vents, I am not getting any hot air at all. The lower cable is attached and I know it is working because I took the underside of the dashboard on the passenger side and saw that it was attached and was pulling the vent door allowing air to come in to the system from the heater core. The troubling thing is that the heater core remained cold (I touched it) all the time even after letting the car run for long periods of time to allow it to reach high temperatures. So I checked the heater control valve and hoses going into the core. Hoses were hot and felt full to the touch. I took the hose going in to the core and saw that coolant was flowing as long as the vacuum little hose going to the heater control valve was on. When it was disconnected the coolant stopped flowing so the control valve is working. What I haven't done yet is to check if the returning hose is flowing (it started snowing and had to stop my troubleshooiting). The only explanation is that the core is plugged but to me this seems very unlikely. It was working perfectly fine last winter. Any other explanations, what else can I look for?. Thanks again!.

CEP89

A plugged heater core is a possibility, especially if you have Dexcool in your system. If it is you may be able to flush it out with a garden hose.