Does your SC Blow hot air on "vent"?

sd_iconoclast

Registered User
I have an '89 SC and the Air Conditioning seems pretty anemic.
I have recently replaced every component in the whole AC system as my system was aflicted with "the black death". I also retrofitted to R-134 at the same time.
Now the AC seems pretty weak. I get temps around 51-55 degrees on hot days.
But I have noticed that warm air blows out of the vents when I set the system to "vent". This seems to be true even on cold days. It is not nearly as hot as if I turn the system to "heat", I wonder if my AC is OK, but it is being forced to cool some pretty warm air to start.
Does anyone else get warm air on "vent"?
Any thoughts on what the problem is?
 
Sounds like your blend door cable may be off. The slider for cold/warm pulls a cable that opens/closes a diverter flap directing air over/through the heater core. You may have a problem there... or possibly under the bottom side of the A/C control panel where the cable attaches.
 
51-55 degrees on hot days is a weak a/c system ??!!

i think thats pretty damn good.

when u have the vent on is it switched to the warm or cool side ?
 
you need to remember the cowl still gets warm air from the engine flowing by it, its probably residual heat from the engine:rolleyes:




-Tony
 
In every position but MAX, outside air is run through the HVAC box to be either heated or cooled. The air is pulled from below the cowl but behind the firewall.

If the gasket that runs along the cowl and seals that area from the engine compartment when the hood is closed isn't fitting tight (aftermarket hood?) then it is very possible very hot engine compartment air gets pulled in, rather than outside air.

When put on max, a flap door closes that causes air from inside the car to be pulled through the HVAC box.
 
Hmmmm Mike...I wonder if that is/was the reason for the solenoid activated slider valve looking thing that someone posted a picture of a while back that was mounted under the cowl pieces and blocked off the air intake vent?????:confused:
 
51-55 degrees on hot days is a weak a/c system ??!!

i think thats pretty damn good.

when u have the vent on is it switched to the warm or cool side ?

My other cars (all late 80s R-134 conversions) are in the range of 41-43 degrees.

Of course, this is with the vent is switched to the cool side. If I switch it to the hot side, the air is HOT!
 
you need to remember the cowl still gets warm air from the engine flowing by it, its probably residual heat from the engine:rolleyes:




-Tony

Actually, I looked at the air intake at the base of the windshield. It is clear to me that it was designed to avoid taking warm air off the engine, which makes sense. Does yours blow hot air on "vent"
 
In every position but MAX, outside air is run through the HVAC box to be either heated or cooled. The air is pulled from below the cowl but behind the firewall.

If the gasket that runs along the cowl and seals that area from the engine compartment when the hood is closed isn't fitting tight (aftermarket hood?) then it is very possible very hot engine compartment air gets pulled in, rather than outside air.

When put on max, a flap door closes that causes air from inside the car to be pulled through the HVAC box.

My first thought was to look at this gasket. I ruled it out as a problem when I realized that the AC was just as anemic when on MAX. I think I will do some tests to figure out if the hot vent air is coming from the heater.
 
I get warm air on vent, but kick the AC on and in the 100 deg Texas heat it will easily blow 42 deg air. On vent I would guess it's blowing about 90+ deg.

I also have a Cervanis hood which could be the issue as stated above.
 
My first thought was to look at this gasket. I ruled it out as a problem when I realized that the AC was just as anemic when on MAX. I think I will do some tests to figure out if the hot vent air is coming from the heater.

Check the lines going to the compressor when you have it on max and fan on high. the compressor should be running, and one of the lines, the one going to the expansion valve should get frosty.

If that's working, but you still get heat, you could have various issues. Note that the "fail-safe" mode of the HVAC system is to be stuck on heat. That way you don't dye of freezing if something goes to heck.

I don't know if there is a easy way to do this. Probably the 1st thing is to get the info to track down if the right vac signal is going to the blend door to the right place. hmm, just got an idea. If you have a vac leak in your system that shows up when you move the lever to vent, you'll bleed vacuum from the system causing the blend door to go to oh heck mode, thus heat.

So I guess I would want to see what the control panel is doing when the switches are flipped. Make sure the blend door maintains it's signal when you move the which door lever around. You may need to pull the dash to find this, I'd start with flopping the glove box door all the way down and looking behind there for anything cracked or leaking.
 
Make sure the blend door maintains it's signal when you move the which door lever around.
On the 90 model, the blend door is controlled entirely by the cable attached to Cold<--->Hot slider bar. The later year climate control units would control the blend door. All other diverters are vacuum controlled. There are only 3 of them. This is why I stated much earlier in the thread to check the cable.. of course, my suggestion appears to have been ignored. :rolleyes: Oh well... not my car, is it? :D
 
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On the 90 model, the blend door is controlled entirely by the cable attached to Cold<--->Hot slider bar. The later year climate control units would control the blend door. All other diverters are vacuum controlled. There are only 3 of them. This is why I stated much earlier in the thread to check the cable.. of course, my suggestion appears to have been ignored. :rolleyes: Oh well... not my car, is it? :D

Apparently it has been ignored. Though that wouldn't explain a behavior of cooling when set to defrost, or defrost/floor, or A/C or MAX, but hotter when on Vent.

Maybe we need the o.p. to try it in all settings and report the behavior.
 
Though that wouldn't explain a behavior of cooling when set to defrost, or defrost/floor, or A/C or MAX, but hotter when on Vent.
Those three settings, by design, also cycle the compressor so there should be some amount of cooling. MAX-AC recirculates the air inside... all of the other settings, including of course vent, pull in air from the outside duct.
Maybe we need the o.p. to try it in all settings and report the behavior.
Yup. It would be helpful to know if the inside air is actually hotter than the outside air and how/if it changes as the blend lever is moved around.
 
On the 90 model, the blend door is controlled entirely by the cable attached to Cold<--->Hot slider bar. The later year climate control units would control the blend door. All other diverters are vacuum controlled. There are only 3 of them. This is why I stated much earlier in the thread to check the cable.. of course, my suggestion appears to have been ignored. :rolleyes: Oh well... not my car, is it? :D

I did not mean to ignore your suggestion. I just did not have any problesm with it. I intend to chek the cable first. Just trying to get to it...
 
Those three settings, by design, also cycle the compressor so there should be some amount of cooling. MAX-AC recirculates the air inside... all of the other settings, including of course vent, pull in air from the outside duct.
Yup. It would be helpful to know if the inside air is actually hotter than the outside air and how/if it changes as the blend lever is moved around.

Thanks guys, I will try this
 
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