1979 El Camino/ Have an AC question/

[Longroof79]

Mando, both blend doors are driven by vacuum. If you look under the dash, you'll see a vacuum servo connected to each blend door. I had the same problem with the air only blowing thru the top and bottom vents, not thru the center dash vents.
I ended up replacing the control unit with one from a junked car. It seemed to do the trick.
It definitely sounds like a vacuum problem. Make sure the vacuum hoses are good, and where they connect together in a plug. I think the small diaphragm pod goes bad. They are not available new as far as I know, or else I'd purchase one.
Check the vacuum feed hoses coming and going. You can also check the blend doors by using a vacuum pump/ brake bleeder connected to the servo. Make sure the doors aren't hanging up, etc.

 

[HAFROD]

Coming from under heater box, you should have two plastic vacuum hoses. One purple or pinkish and one gray. The gray goes to your heater valve in your heater hose to intake. The pinkish or purple goes to full engine vacuum. Purplish or pinkish goes to a small vacuum canister on the heater box and out to carb vacuum. My vac can is broke so its hooked straight to vacuum on carb.

 

[HAFROD]

I think its the purple or pink vac hose that operates the middle dash vents so it has to be hooked up

 

[pontiacgp]

I think its the purple or pink vac hose that operates the middle dash vents so it has to be hooked up

The pink one is the vacuum source that comes from the engine bay so it must be the purple one

 

[HAFROD]

I may need to clarify, two hoses only, there is a gray vacuum line and a purple vacuum line on my 81 El Camino and my 78 Olds Salon. Gray is heater valve and purple is engine vacuum. No pink hoses. I have an old heater box in my junk pile that appears pink. Don't know if they changed the line color in the later years or if it's faded from heat or sun from mine sitting in the junk pile. So to sum it up, gray to heater and the other color to engine vacuum through the vacuum canister. It can be direct to engine vacuum if your canister is leaking or broken.

 

[mando13]

Ok Guys, this is what I found. I cleaned all the vacuum hoses in the control head but still no go.I did find out that the purple line is the main source of vacuum coming in.It goes into a small vacuum line switch that is part of the control head.After starting the engine up and putting the switch on AC,I noticed that there is no vacuum going to the line feeding the center door.I cleaned the vac.switch really good but that did not help.However,If I take the purple line (Main Vac) line and couple it to the line that goes to the center blend door,it will open up really nice.I tried it a few times and it still opens up ok.If I connect the line back to the vac.switch,I loose vac.again and of course,the door will not open.Therefore,Looks like I have a bad Vacuum switch in the control head.Darn it,I just paid about $90.00 for this used control head on Ebay.Its been about 4 months so no more guarantee.
I am going to check around and see if I can find a new vac. switch but if not,back to the junk yard.
Thanks to all of you for your kind help,tips,and suggetsions.
Mando

 

[mando13]

Hello everyone here at the forum.Well, after more troubleshooting,I found out that the reason that door in the middle behind the center vents is not opening is because of no vacuum from the vacuum mode switch.This switch is at the control head and delivers vac. as you select a setting.What I did to verify the problem was,I took the main vacuum source line (Purple Vac.Line) and coupled it directly to the servo that controls that particular door.As I did that,the door opened up really nice.I shut the AC off,door closes and than turned the AC on again,door opens up nice.I called all the parts houses here in town and nobody had or could order the vacuum switch for me so I went to the junk yard and found another one off a 1983 chevelle.Its pretty dirty but I am hoping that after a good cleaning,it will be ok.
Oh,by the way,since I am here posting,If any of you have the same truck or car of this era,can you please give me the routing of the V belt for the Air compressor.The reason I am asking for this info is because there was no compressor on it when I first bought the truck.
I have the power steering,water pump,and the AC compressor.No smog or air pump.Correct me if I am wrong but this is the way that I have it routed right now.From the crank pulley,goes around the water pump pulley,goes around the AC compressor,goes under the power steering pump,and back to crank pulley.In other words,the belt is wrapped around the water pump,the power steering,and the AC compressor.Of course,thats after starting at the crank pulley.A guy here in town told me that it does not wrap around the water pump.He says that it should involve the crank,the power steering,and the compressor so now he has me wondering.If you guys can help with a drawing or a picture of how this belt is routed,I would really appreciate it very much.Thanks in advance.
Mando

 

[Texas82GP]

Check out the pictures in post number 18 in this thread. I think they are what you are looking for on belt routing....

https://gbodyforum.com/threads/r4-a-c-compressor-bracket-configuration.56010/page-2

 

[mando13]

Thank you very much Texas 82, that's just what I needed.That confirms that the way I have it routed right now is correct.
One more question? I'm in the process of cleaning the vacuum switch.Do you have any idea's what to use on it to clean all that dirt of it?I did use air to get most of the dirt off but I wanted to use some kind of spray inside the switch to make sure it works ok.
I have already cleaned all electrical contacts with contact cleaner.I just need to clean the vac.switch.Thanks again.
Mando

 

[Texas82GP]

Thank you very much Texas 82, that's just what I needed.That confirms that the way I have it routed right now is correct.
One more question? I'm in the process of cleaning the vacuum switch.Do you have any idea's what to use on it to clean all that dirt of it?I did use air to get most of the dirt off but I wanted to use some kind of spray inside the switch to make sure it works ok.
I have already cleaned all electrical contacts with contact cleaner.I just need to clean the vac.switch.Thanks again.
Mando

I have used some stuff called Deoxit on old electric switches with great sucess. It seems to be safe to use on plastics. It leaves a very slightly oily residue though. It is a little hard to find but you can find it online and guitar center sells it. The guitar folks swear by it for cleaning switches and knobs on guitars and amps. Other than that I'd be pretty careful. I'd probably just use a soft toothbrush and distilled water in a spray bottle to clean the accessible outside portions of the switch. You might be able to do some good with careful use of a pipe cleaner. Just some ideas. I would propably go for the deoxit since I already have some.