'86 A/C Control Woes...
Thread Starter
Instructor
Joined: Nov 2012
Posts: 119
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'86 A/C Control Woes...
I topped off the R12 the other day and got it blowing nice, cold air. I noticed that the cold air seems to come out "everywhere"...like the lever in the dash does nothing but turn the A/C on. It won't divert it to any of the specific regions. Any advice?
I also only have high speed on the fan. I replaced the rheostat to no availe. Any help is GREATLY appreciated. Thanks in Advance
I also only have high speed on the fan. I replaced the rheostat to no availe. Any help is GREATLY appreciated. Thanks in Advance
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
The various doors in the HVAC system are controlled by vacuum. If you don't have vacuum at the control head then you won't be able to change the HVAC mode. That's usually caused by a bad vacuum check valve (next to the distributor on the driver's side), a $4 part at any auto parts store. Also check the various vacuum lines to make sure they're OK.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
The various doors in the HVAC system are controlled by vacuum. If you don't have vacuum at the control head then you won't be able to change the HVAC mode. That's usually caused by a bad vacuum check valve (next to the distributor on the driver's side), a $4 part at any auto parts store. Also check the various vacuum lines to make sure they're OK.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
"I also only have high speed on the fan" tells me he doesn't have the lower speeds when selected.. but he can select high which is a circuit into it's self..
OP could you describe your fan problem.
Race Director
Joined: Apr 2002
Posts: 10,036
Likes: 346
From: Anaheim CA
There are two scenarios here
1 - Fan runs on high speed no matter what position the fan switch is put into.
2 - Fan does NOT run when the fan switch is put in one of the lower speed positions. It DOES run in the HI position.
I was thinking #1. Didn't think of #2.
He said:
I suggested a shorted relay, and...
Looking at the wiring diagram, you're right.
Here's a diagram I found somewhere:
1 - Fan runs on high speed no matter what position the fan switch is put into.
2 - Fan does NOT run when the fan switch is put in one of the lower speed positions. It DOES run in the HI position.
I was thinking #1. Didn't think of #2.
He said:
I suggested a shorted relay, and...
Looking at the wiring diagram, you're right.
Here's a diagram I found somewhere:
Last edited by Cliff Harris; Jul 19, 2013 at 10:44 PM.
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Race Director
Joined: Aug 2007
Posts: 11,889
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From: Whitefish Falls Ontario
St. Jude Donor '08-'09
This drawing is for the 84 but the circuit and wiring is identical to the 86. Time for a meter to check resistances and voltages. Obviously the relay works for the high setting, normally when none of the lower speeds work, the problem is the blower resistors. With a meter on the ohms scale check for resistance from the blk/red wire at the blower to the drk/blue on the resistor, not sure of the value but if infinity, either problem with relay n/c contact or broken wire. With setting for one of the lower speeds you should get a voltage reading between ground and the dark blue on the blower resistors and the n/c contact of the relay..
Race Director
Joined: Aug 2007
Posts: 11,889
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From: Whitefish Falls Ontario
St. Jude Donor '08-'09
Melting Slicks
Joined: Aug 2008
Posts: 2,082
Likes: 50
From: Palmdale CA
I think we covered this.
Thread Starter
Instructor
Joined: Nov 2012
Posts: 119
Likes: 0
The various doors in the HVAC system are controlled by vacuum. If you don't have vacuum at the control head then you won't be able to change the HVAC mode. That's usually caused by a bad vacuum check valve (next to the distributor on the driver's side), a $4 part at any auto parts store. Also check the various vacuum lines to make sure they're OK.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
Only high fan speed is usually a bad relay. It's mounted on the firewall next to the blower motor.
. I'll pick up another one later this week.
Le Mans Master
Joined: Dec 2000
Posts: 7,839
Likes: 22
From: San Diego, Ca
With a new Resistor Pod, I'd guess a bad Blower Switch. Brief search of ac delco's web seems to show that it's still available. Get the part # and a competent Parts Counter person might be able to get it for you. You'll have to get the Center Panel Off to access the controls, but it's not a difficult repair.
Thread Starter
Instructor
Joined: Nov 2012
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Ordered a blower switch.
Interesting find on the HVAC doors. They are controlled by vacuum...a small rotaty switch w/ a toothed rack on the back of the heater control module. Mine had a small piece of tie-wrap stuck between the 2 and the teeth wouldn't engage. I removed the offending piece of plastic...but the teeth still wouldn't engage. I found a thicker piece of plastic and placed it under the rack...so it would engege the teeth on the rotary dial for the vacuum control **** and..... VIOLA! Heater control is functional and bi-level, vent and defroster all work as they should. I even scare myself sometimes!
Interesting find on the HVAC doors. They are controlled by vacuum...a small rotaty switch w/ a toothed rack on the back of the heater control module. Mine had a small piece of tie-wrap stuck between the 2 and the teeth wouldn't engage. I removed the offending piece of plastic...but the teeth still wouldn't engage. I found a thicker piece of plastic and placed it under the rack...so it would engege the teeth on the rotary dial for the vacuum control **** and..... VIOLA! Heater control is functional and bi-level, vent and defroster all work as they should. I even scare myself sometimes!
