A/C guys....I need your help please.

[trevor73402]

Hi all,

I have a few bugs in my A/C that im trying to get worked out since "hot" weather as arrived in southern oklahoma. The truck is a '84 K10 SWB. The A/C blows cold air, there are just a few problems.

1.) This seems to be a common problem.....most of my air is blowing out the bottom floor vent. Ive seen many people talk about this, but ive never read how to actually fix it? I have air coming out the top vents, just not very much.

2.) When the A/C is turned on, the truck runs/idles at alot higher RPM, but it stays on high idle even when the compressor kicks off. It never drops down as the comp cycles on and off. Is this normal?

3.) Lastly, and most odd of all. On my A/C control panel the "Off" setting will not shut the compressor off from cycling. The air will stop blowing from the blower, but the comp continues to cycle in and out on the "Off" setting. I have to slide the lever over to the "Vent" setting to get the compressor to shut completly off and stay off. Max and Norm settings work correctly as they should, but for some reason the "Off" setting is not shutting the comp off??

This is a factory A/C setup. Any and all help on these issues would be greatly appreciated.
Thanks,

[draggin86]

im sorry i dont have any answers for you but your truck looks great!

[CaliDude76]

You know.. it seems that you have a vacuum problem somewhere... I've had to pull out the whole distribution box out of my 84, to replace the heater core... and it was all vacuum driven. There's little vacuum pods that actuate the flapper doors inside the box, via when you flip it to heater, or a/c or defrost mode. You very well may have a disconnected hose under there.. or a leak in one.. that may not be giving it enough umph to flip the lever to distribute the air up on thru the dash vents. Also.. there's vacuum lines that run behind your Temp control deal itself.. if your having problems with it not shuttng the comp off... it might be that whole unit itself.. might have to replace, or get a second hand one from the junk-yard for cheap.. just to see if its that... also.. check to hear for any constant 'hissing' noise from either your dist box.. or temp control... possible clue for a leak. good luck

[CaliDude76]

As far as the idle situation.. in my truck.. there's a little actuator sitting in front of the throttle on the carb. When you kick on the A/C. a plunger pushes agianst the throttle to raise R.P.M.'s.. G.M's solution to Compressor Lag.. (Pre-TBI)... I had the same problem with mine... thing is.. is that when you turn the A/C off it's suppose to flick back off of the throttle automatically.. but it didn't.. I had to open the hood and push it back by hand... these were problematic... for me anyway... I just went without.. and during summer raised the throttle just a bit to compensate for lag. Stuck a 350 in it.. and no problems with the A/C... it was the 305 that gave me problems

[tucsonjwt]

I don't know what is wrong with your truck, but here is what I experienced with my 83 C20.
Airflow to the upper vents in the dash was restricted by the hoses and vent ducts not being completely connected. I took out the dash pad, glove box, etc. and started following the ducts and hoses to make them secure. I used HVAC type silver tape to wrap up the connections to make sure that they did not slip loose. I also added some foam type house door insulation where the ducts did not seat firmly against the dash. The factory used foam to help seal these gaps also. If you look at the duct system, you will see that the ducts and hoses just barely fit together loosely - not a very good set up.
I have my carburetor set to a low idle. The fast idle solenoid on the carburetor for A/C operation does not add much to engine R.P.M. Still, when I come to a stop at a traffic light, the engine revs higher than normal, when the A/C is not on. I think the throttle linkage is sticking somewhere, but I just jab the accelerator a little and it returns to its normal low idle. If the A/C is on, I just don't jab the accelerator and the idle is high enough to keep it from stalling. As far as I am concerned, as long as the engine doesn't stall at idle with the A/C on, I don't care if the fast idle solenoid works. I would look at capping off that fast idle solenoid and increasing the throttle screw slightly - or replace the fast idle solenoid.
If your compressor will not shut off when the dash control is in the off position, I would think that the switch is not functioning in the off position.
Obviously, an auto A/C guy is the person to talk to, but they usually don't work cheap, and you can replace a lot of parts for the cost of a diagnosis/misdiagnosis from a professional. They also make a lot of money off their markup on parts - if they can find them. I would check your ducts/connections, fiddle with the fast idle solenoid, and price a new HVAC switch or possibly replace the whole assembly, before I spent money on a pro.
BTW, the vacuum lines under the dash are a tiny diameter and I have not found anyplace that sells them. Also, it looks like major disassembly would be required to trace them all.
Good luck.