help with A/C control please,,,,,,,,,,,

olskool

Apprentice
Sep 26, 2021
55
18
i have a 1986 monte carlo ss, i am sure this is a common thing. the A/C blows in the floor only. i was told that it was the "rotary switch" is that the proper name? and might that be the problem? any help is greatly appreciated. i have helped a couple of folks on here with transmission questions, i have 45 years' experience as a professional rebuilder. so, if i can return the favor i will be glad to.

thanks mike
 

Oldcarjunkie

Apprentice
Supporting Member
Feb 4, 2022
64
18
Fate,Texas
i have a 1986 monte carlo ss, i am sure this is a common thing. the A/C blows in the floor only. i was told that it was the "rotary switch" is that the proper name? and might that be the problem? any help is greatly appreciated. i have helped a couple of folks on here with transmission questions, i have 45 years' experience as a professional rebuilder. so, if i can return the favor i will be glad to.

thanks mike
I believe it's called heater door blend actuator or just actuator.
 
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melloelky

Comic Book Super Hero
Oct 22, 2017
3,703
113
mass
yes usually when that switch leaks(as it's a rubber diaphragm)it'll default to floor and defrost.
 

Oldcarjunkie

Apprentice
Supporting Member
Feb 4, 2022
64
18
Fate,Texas
Could also possibly be a disconnected vacuum line running from passenger side of firewall engine compartment. Small pinkish line I think.
 
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57 Handyman

Greasemonkey
Feb 6, 2017
243
63
That problem is related to the blend door actuators not opening/closing properly in the HVAC. In order to verify that malfunction, you'll need to check and test that the vacuum system has no leaks. Vacuum is how the 3 actuators direct fan air flow through the HVAC.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,613
113
That "disk" is part of the function control switch to determine vacuum path to operate the vacuum pods in each mode. If you find a new one, you will likely pay out the nose for it, unfortunately. Used to be a $9 part. Best price I've seen lately is $75 plus shipping. GM p/n 16037778.

It COULD just be a problem with the dual vacuum actuator pod with the yellow/red lines going to it. It controls the lower door which fortunately, isn't that tough to reach. GM p/n 1996729 if you need one. They can be found on other G-bodies and possibly earlier 70's A-body cars. According to the parts information, older part numbers were 1996574 and 1996628. An interesting thing is that the older parts BOOKS show 1996564 was used on the A-body cars. Which has a different actuator arm than the later G-body. So if it's not a 1996729, not sure if it would have the right connector on the business end. It's going to be a PITA no matter what the issue is here.

This may give a bit of insight.
HVAC.jpg


They call it the lower mode valve. See the locations here.

AC vacuum lines.JPG
 
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SS_Malibu

G-Body Guru
Sep 27, 2021
520
93
Mesa, AZ
That "Disk" that 69hurstolds is talking about was a problem with mine. I went wrecking yarding and found one out of a front wheel drive late 80's Chevy that had the same looking controls and pulled it off of that control. Yes, that disk just "followed" me home and I've gave it the love it deserves ever since. Now I need to fine those plastic purple and tan colored vacuum hoses the run from the control switch in the dash to under the hood to the vacuum ball and heater control switch.
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,613
113
Just make sure you get the correct 9 port, otherwise it'll fugg up your day.

For the price of the new selector switch nowadays, you can get a complete used unit that's probably in good shape. Most of the time, the plastic center clip gets brittle and breaks, and some have said to just replace it with a screw and nut. The 2-port jobbie solely for the water valve is also a booger to find new as well.
 
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