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On my 81 Vette the AC blows cold air as it should but, when I shut it off, I get hot air in the cabin. The hot air does not come through the vents on the dash, It comes from the floor somewhere. I have replaced the hot water shut off valve. So I'm struggling to see what is causing this issue.
You replaced the hot water shut off. Did you test the vacuum line to it to make certain the switch on top the heater box is actually working properly and the vacuum line holds vacuum?
Have you felt the return heater hose to see if it remains cool?
Do you have general heat coming through the floor pans that 99 percent of all C3's have? Have you added any heat and noise insulation to your floors and firewall? Is the foam heat collar still in place over the bellhousing?
4-Vettes, Correct, I will be checking the hot water shutoff valve this week to ensure proper operation. And I know for a fact there is no insulation on the bellhousing. Thanks for this and I'll post after these task are performed. Thanks again.
Could be the side vent door (gaskets) are shot. They're down by the drivers/pass' feet. Easy to rebuild with some $2 foam from a sewing or craft store.
5 inches of vacuum is extremely low you do know? Correct?
your engine idles at how many inches of vacuum? A totally stock setup around 18 inches.
A car with a nice street performance cam, around 14 inches of vacuum.
So, you have vacuum to the hot water shut off valve although it is VERY slight. Have you tested if it is actually able to shut the hot water off? Those heater hoses should remain cool to the touch if no water is flowing through them.
Reach behnd glove box and force shut off valve / plunger and recheck vacuum. If better adjust cable to force plunger and hot water shut
off.
i would also add shut off valve as when you shut off car vacuum is lost and it opens some anyway.
The cold lever should not hot the left side of bezel. That is the push for the plunger.
Ok, A couple of things I noticed. First, the vacuum hose for the a/c is currently connected to port on the carburetor, I think that should be manifold vacuum. right? Next, question - can the heater shut off valve be connected backwards? or does it really manner?
Are you getting hot air? As in moving, blowing air?
Or is the heat more like radiating from the tunnel? You may have air leaking in through the firewall.
Those vacuum water valves are crap. I tried several on my 82 and they always flowed water. I also installed a shut off valve and it really made a huge difference in the heat by my feet.
I installed one with a bar type handle I could remove in the summer for cosmetic reasons. I would hit the occasional car show with 82CE. I just put it back on the fall/winter. If you look close you can see it.
Ok, Sorry for the late post, but I have finally found the issue. I smoked tested the entire vacuum and discovered that the AC vacuum selector switch in the dash and the hotter vacuum cutoff switch were both leaking. New switches have been ordered and after installing them, I'll smoke test it again and post the results.
Ok, Sorry for the late post, but I have finally found the issue. I smoked tested the entire vacuum and discovered that the AC vacuum selector switch in the dash and the hotter vacuum cutoff switch were both leaking. New switches have been ordered and after installing them, I'll smoke test it again and post the results.
Thanks,
Both of those switches do have exhaust ports.
The hot water vacuum switch is easy to troubleshoot but the rotary vacuum switch is more complex.
Keep your old parts...
Agreed, I always keep them. The vacuum switch had several leaks, The main connector ( corrected now) and the rubber disc. the hot water vacuum switch was leaking for around the shaft, brings shot!!
Update, I changed the hot water vacuum switch (mounted on top of the ac box). And a new problem (of course) The new vacuum switch will not stay the fully engaged. It's almost like the spring on the vacuum switch is too strong and is pushing it open. Is there an adjust on the cold/hot cable to increase the tension? the below photo is the vacuum switch I used.
Update, I changed the hot water vacuum switch (mounted on top of the ac box). And a new problem (of course) The new vacuum switch will not stay the fully engaged. It's almost like the spring on the vacuum switch is too strong and is pushing it open. Is there an adjust on the cold/hot cable to increase the tension? the below photo is the vacuum switch I used.
81 Corvette HVAC Issue
