'79 Cabin Heat
Thread Starter
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
'79 Cabin Heat
Happy New Year!
I know this has been covered, I did a search but couldn't find exactly what I was looking for.
My 79 blows heat out of the vents constantly. Currently my AC is not functioning, but I will save that for another thread. Yes, I do know that on a 79 the fan blows constantly, even when it's 'off'.
The hood wasn't fulling closing, so I adjusted the latches to make it a tighter fit. My thought process was that engine heat is being drawn in to the vents...but that was no help.
Today, i removed the coolant shutoff valve, to make sure that was working. With the valve out, and heater hoses plugged, i tested it with a vacuum pump, it works fine. Then, I started the car, and plugged in the vacuum line. It defaults to closed, and when I move the heater control to heat, it opens... so that is not the problem.
I know there is an adjustment on the cable for the that controls the 'blend'. Could that be whats causing the problem? I have adjusted it previously.... so i don't think that is problem, but I could be wrong.
If it's not the cable, what are the next steps?
And advise is appreciated.
I know this has been covered, I did a search but couldn't find exactly what I was looking for.
My 79 blows heat out of the vents constantly. Currently my AC is not functioning, but I will save that for another thread. Yes, I do know that on a 79 the fan blows constantly, even when it's 'off'.
The hood wasn't fulling closing, so I adjusted the latches to make it a tighter fit. My thought process was that engine heat is being drawn in to the vents...but that was no help.
Today, i removed the coolant shutoff valve, to make sure that was working. With the valve out, and heater hoses plugged, i tested it with a vacuum pump, it works fine. Then, I started the car, and plugged in the vacuum line. It defaults to closed, and when I move the heater control to heat, it opens... so that is not the problem.
I know there is an adjustment on the cable for the that controls the 'blend'. Could that be whats causing the problem? I have adjusted it previously.... so i don't think that is problem, but I could be wrong.
If it's not the cable, what are the next steps?
And advise is appreciated.
Last edited by blk79nj; Dec 31, 2018 at 11:51 AM. Reason: spelling error
Instructor
Joined: Jan 2010
Posts: 129
Likes: 4
From: Perth western Australia
I have the same problem in my 79, worked out its the heat form the engine bay coming thru the vents.
No matter how much I tried to seal it with thicker foam around the lip it is still getting hot air in.
Now I drive with the bonnet popped and all the heat goes out the gap and not into the cabin.
Not a look everyone likes but it solves the problem on a long drive.
No matter how much I tried to seal it with thicker foam around the lip it is still getting hot air in.
Now I drive with the bonnet popped and all the heat goes out the gap and not into the cabin.
Not a look everyone likes but it solves the problem on a long drive.
Melting Slicks
Joined: Sep 2006
Posts: 2,815
Likes: 470
From: Wichita Kansas
I found quite by accident this summer that if you turn the vent on, just to low, it helps, because then the air you get is at least from outside and not the engine bay. You can even shut the vents or diverters or aim them away from you, but at least it changes the source from the hot hot engine bay to just the hot outside air. I don't know how many times I have wished that Chevrolet had never come up with their 'flow-thru ventilation'. I suppose they were only trying to help keep us safe......
Race Director
Joined: Mar 2017
Posts: 11,949
Likes: 4,507
From: Virginia
Are you certain the heater core valve is blocking 100% of the coolant? Check the temp on the outflow hose after the car has been running. I bypassed the cores in my vehicles, and it made a tremendous difference.
Racer
Joined: Dec 2014
Posts: 402
Likes: 44
From: Pittsburgh PA
I would start with checking the hot water valve which is located on the right rear side engine compartment. This valve work off the vacuum from the engine is held closed by vacuum when the temp lever is on cold. When you move the lever to hot it shuts off the vacuum and the valve opens. If valve is not getting vacuum or the diaphragm is bad it would be in an open state all the time. You can use one of those hand held vacuum pump testers to see if the valve is working like it should. After that you should check all you vacuum lines going to and coming from the climate control in the center console.
Ken
Ken
Thread Starter
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
I would start with checking the hot water valve which is located on the right rear side engine compartment. This valve work off the vacuum from the engine is held closed by vacuum when the temp lever is on cold. When you move the lever to hot it shuts off the vacuum and the valve opens. If valve is not getting vacuum or the diaphragm is bad it would be in an open state all the time. You can use one of those hand held vacuum pump testers to see if the valve is working like it should. After that you should check all you vacuum lines going to and coming from the climate control in the center console.
Ken
Ken
Drifting
Joined: Jun 2004
Posts: 1,881
Likes: 9
From: staten island ny
the heater valves are notorious for hot water bypassing the valve and heating the cabin, the standard fix is to cut both heater core hoses, use gates or ball valves with some short nipples from Lowes and shut them during the summer....
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Safety Car
Joined: Sep 1999
Posts: 4,910
Likes: 698
From: grand rapids, lowell mi. area
well yrs. ago ,I put a shut off valve on the rubber pipe running to the heater outside by the motor,then when it started to get cold I could open the valve and there would be heat again from my heater!
Advanced
Joined: Jul 2017
Posts: 68
Likes: 59
From: Dallas Texas
I just searched for this thread...I gonna install gate valve to shut off hot water to the cockpit on my 75 with A/C but thought only the top hose would be enough to stop the flow. Don't know much about nuthin, so why install on both hoses? Thanks in advance!
Drifting
Joined: Apr 2004
Posts: 1,424
Likes: 127
From: Mequon WI
You tested the water valve outside the car, right ? And you did not indicate that you have air only from the defroster. This tells me that your valve works, tour vacuum works, your control works.
I suggest removing th glove box. Behind it you will find where the temp cable attaches to (1) a vacuum valve that feeds vacuum to the water valve. This cable also attaches to the damper that regulates the source of air outside or over coil.
You could very possibly have a disconnected cable. Easy, cheap fix.
You could also unplug the vacuum line at the water valve. You should have vacuum when the temp lever is fully left on cold. No vacuum would indicate a disconnected cable or a bad switch behind the glove box.
Lastly there is a diverter valve in the passenger football. That could be bad but I would suspect that last.
Goo Luck.
I suggest removing th glove box. Behind it you will find where the temp cable attaches to (1) a vacuum valve that feeds vacuum to the water valve. This cable also attaches to the damper that regulates the source of air outside or over coil.
You could very possibly have a disconnected cable. Easy, cheap fix.
You could also unplug the vacuum line at the water valve. You should have vacuum when the temp lever is fully left on cold. No vacuum would indicate a disconnected cable or a bad switch behind the glove box.
Lastly there is a diverter valve in the passenger football. That could be bad but I would suspect that last.
Goo Luck.
Thread Starter
Pro
Joined: Aug 2007
Posts: 707
Likes: 31
From: Pitman NJ
I tested the valve outside the car, with the car running using the heater controls (i pinched off the heater hoses).
I also have somewhat of an update. I noticed that the foam piece on the lower AC line going into the box was hanging out of the hold. It was sucking air in through it with the fan blowing. I cut a new piece of foam, and used some heat tape to hold it in. It has helped, but i'm still getting some heat.
I have also since replaced all the o-rings, the oraface tube, receiver/dryer and the soft AC lines. I am getting the AC charged on Tuesday, crossing my fingers that the compressor is good.
I also have somewhat of an update. I noticed that the foam piece on the lower AC line going into the box was hanging out of the hold. It was sucking air in through it with the fan blowing. I cut a new piece of foam, and used some heat tape to hold it in. It has helped, but i'm still getting some heat.
I have also since replaced all the o-rings, the oraface tube, receiver/dryer and the soft AC lines. I am getting the AC charged on Tuesday, crossing my fingers that the compressor is good.
Last edited by blk79nj; Mar 31, 2019 at 09:04 PM.