Factory AC and Heater help

[Richard H.]

It seems as if I have run into another little snag from my trucks previous life. In April I was going to swap out my engine for my new 383 and decided to re-do every thing up front from the ground up. My first clue that it had been wrecked once was the pass side fender was once white not the original ochre. Then yesterday I noticed the cab had been mashed a little near the heater. The AC control valve (door) was kinda knocked around also. Can I do away with this or seal it permanently ? I Don't care about outside air or venting. Also if I seal the door in the kick panel while I'm at it will the ac , heat and defrost all still work?
I have to patch where the fan motor seals , can't see it in the pic but it warped pretty bad and maybe cut in new metal in the corner where the most damage is if there isn't enough air flow. I am assuming both ac and heat recirculate the cab air?

[Richard H.]

ttt

[JimKshortstep4x4]

My suggestion would be to fix the truck in the damaged areas. Sealing the flapper valve to prevent outside air from coming in is possible but not recommended. Sealing off the passenger side vent door will stop the air recirculation.

Jim

[Richard H.]

Got any reason for why it would not be recommended to seal the ac valve? Also I can't really tell where the fan gets it's supply. I can see the small steal ductwork that feeds but not the supply. Lmc calls the seal an AC shut off ??? Does that mean it has to have fresh air? Don't seem to efficient.

[JimKshortstep4x4]

The fan gets its air supply from the cowl area, (outside air) or the right side vent, (inside air). Blocking one or both will effectively stop your fan from blowing air.

The outside air is blocked by the closed flapper valve when the AC is on so that recirculated air is used. The flapper door is open when the heater is on so outside air is used.

Here is the vacuum control schematic.

Jim

[GMC Jim]

Previous owner of my truck had cut the refrigerant lines to the evaporator and removed the compressor and condenser. I used condenser, compressor, evaporator and hoses from a 1971 Pontiac. ( The parts were interchangeable. ) I also removed the outside air door and diaphragm and plugged the vacuum hose; leaving vacuum to the water valve as required. I also disconnected the recirculated (inside) air vacuum lines and sealed the door in closed position.
This ensured that all air to the heater/ air cond system was outside air. This simplification of the air intake system has worked out very satisfatory. I also mounted a toggle switch which turns compressor on/off; on the under lip of dash just below the air cond./ heater control assembly.
This arrangement gives control to the system; heated, air cond or plain outside air thru the outlets; heater, air cond or defrost. Using outside air as a source for the system keeps a supply of fresh air in the cab at all times. If you or any of your passengers are smokers; keeping the cab interior with clean outside air is quite desirable, next to a necessity!........... Jim

[GMC Jim]

I might add that the modifcation described above was done over 10 years ago; with no regrets..The vacuum lines are simplified...Vac source to vac reservoir, to control head vac switch. From the vac switch a line to water valve.

[Richard H.]

Originally Posted by JimKshortstep4x4

The fan gets its air supply from the cowl area, (outside air) or the right side vent, (inside air). Blocking one or both will effectively stop your fan from blowing air.

The outside air is blocked by the closed flapper valve when the AC is on so that recirculated air is used. The flapper door is open when the heater is on so outside air is used.

Here is the vacuum control schematic.

Jim

Thanks , good explanation and I also saw some good pics from you in the search area.

[GMC Jim]

Richard H.---I disagree that blocking one or both will stop the fan from blowing air.... As I stated, my system uses outside air exclusively with no restriction.... Either inside air OR outside air can be used quite satisfactorily. As long as either outside air or inside air is used, the fan will operate normally.... Jim

[Richard H.]

GMC Jim ,sorry for not posting back yesterday You are both saying the same thing about the vents and I am going to hook it all up stock. Then I will find away to disable the outside air for my self and if there is a next owner he can have it his way. I will also come up with a way to run the ac pump while in defrost mode.
Thanks for your help RH

[GMC Jim]

Rich, would be simple to disable the outside air door operation. As I recall the door is open except when vacuum is applied. If you would want the door to remain open; all your would have to do is to remove the vacuum line at the door and plug the hose. And if you want to control the compressor just mount a switch that is fed with 12 volts from the fuse panel and the other end of the wire to the compressor that controls the compressor clutch. You could then remove and tape the existing wire. This will then give you control of refrigerated air at any postion of the heater/air dash contols. Good luck to you on this, as you can see that the operation of the system is dependent upon how you select the vacuum to the design functions........Jim

[Rickey]

Someone messup the heater contols on my truck, I had to tyrap the heater control valve closed so the heater would not work. Where can i find a diagram on the heating and a/c system for a 70 swb.

[Andy4639]

The A/C only works when the factory switch on the back side of the floor vent is activated by the cable pushing the switch in. This is where I hooked my fan motor wiring into also to turn the fan on when the compressor is activated. The fan is hooked to a relay but feed from here. Just remove the factory switch and add the toggle to the dash. I have been considering doing this but haven't gotten it done yet.

[GMC Jim]

Andy, my previous msg states the advantage with the versitality and convenience of simply controling the A/C compressor with a switch. I mounted the switch on the dash lip just below the existing fan speed switch. The relay controls only the high speed fan; lower speeds are controlled by the resistor pack mounted in the top side of the plenum in the air distribution duct in the cab. 3 wires plug into this resistor pack; a 14 gauge yellow wire, a 14 gauge dark blue wire and a 16 gauge light blue wire. Hope this helps clarify the modification I have previously outlined.
Rickey, the GM "Truck Chassis Service Manual", contains the wiring diagram for the air conditioning system. If you don't have this manual, send me your address and I will mail you a copy of this diagram.......... Jim

[Andy4639]

GMC JIM, I have the shop manuals. I'm talking about the little push button switch on the back of the black box on the floor. The cable that runs from the dash right behind the duct work. If this switch isn't ingaged then the compressor will not run.