Hot Air thru Vent w/temp on Cold?
05-27-2007, 10:25 AM
#1
CF JASOC Member
Thread Starter
Hot Air thru Vent w/temp on Cold?
'71 A/C car.
Everything appears to be functioning properly, but when set to Vent/Cold the air coming out of the vents is Hot. When set to A/C, it blows plenty cool, but I think it may be fighting the heater core.
Can't see the cable that goes to the plenum door, but I can hear it moving from one stop to the other behind the dash. The hot water valve behind the right fender vent is getting vacuum, but can't tell if it is closing (or opening) the valve.
I believe that the control head wheel set to Heat just moves the plenum door, and the temp wheel set to Hot opens the hot water valve. Is this an incorrect assumption?
Question: If the hot water valve isn't working, could this be my problem even if the plenum door is moving as it should since hot water may still be flowing through the heater core?
The pictures in the GM manual seem to do a resonably good job of showing everything except the cable going to the plenum door. Anybody got a pic of their dash apart that shows it?
Thanks.
Everything appears to be functioning properly, but when set to Vent/Cold the air coming out of the vents is Hot. When set to A/C, it blows plenty cool, but I think it may be fighting the heater core.
Can't see the cable that goes to the plenum door, but I can hear it moving from one stop to the other behind the dash. The hot water valve behind the right fender vent is getting vacuum, but can't tell if it is closing (or opening) the valve.
I believe that the control head wheel set to Heat just moves the plenum door, and the temp wheel set to Hot opens the hot water valve. Is this an incorrect assumption?
Question: If the hot water valve isn't working, could this be my problem even if the plenum door is moving as it should since hot water may still be flowing through the heater core?
The pictures in the GM manual seem to do a resonably good job of showing everything except the cable going to the plenum door. Anybody got a pic of their dash apart that shows it?
Thanks.
Last edited by xCCTer; 05-27-2007 at 10:34 AM.
05-27-2007, 11:04 AM
#2
Le Mans Master
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Yes the valve may not be closing and causing a problem. Easy to verify, bypass it. Also the fresh air door may not be closing all the way, mine is hosed up from the factory, with it closed there is a 1/2 inch gap along part of the lip. Have not thought much on how to fix it yet
05-27-2007, 12:20 PM
#4
Safety Car
I had the same problem--the annoying hot air coming from the vents--most noticeable with t-tops off.
Here is an experiment I performed to find the cause:
After insuring all a/c system vacuum actuated flappers/doors were operating correctly:
And--after completely disconnecting the heater core from engine coolant--I removed and capped the heater hoses.
Fan Speed on HIGH. Selector set to VENT. Hood seal installed correctly and brand new.
1. I measured temperature coming from the center vent. When engine was cold the thermometer read ambiant outside air temperature.
2. As the engine/engine bay heated up, the temperature slowly rose to 25F above ambiant--causing annoying warm air to enter the cabin.
* Remember, there was no possibility of the heater core being the problem as hoses were completely disconnected.
** I checked to see if air was being sucked from the engine bay into the evaporator fan thus causing the heat. I did this by placing the selector on MAX (recirc), then closing both windows except for a crack at the top of one. Then I blew smoke to see how much air was leaving the cabin. It turned out extrememly little--I have a well sealed system. If it had been sucking engine bay air, it would have pressurized the cabin and forced the air out the through crack.
3. I then put a 8 x 8" x 0.035" sheet of titanium (aluminum would work as well, I just happened to have the piece lying around) between the exhaust manifold and evaporator case. Air temperature slowly dropped 7F.
4. I then put pipe insulation on the aluminum refrigerant lines coming out from the evaporator--this dropped the air temperature another 10F--but much more rapidly.
5. I then covered the entire evaporator case and fan motor with high temperature insulation--from Summit.
Problem solved--ambiant temperature air now coming from the vent (2-3F rise is all that I measured).
Also, now a/c air is much colder at warm startup and 7F colder running.
Conclusion:
Heat is conducted 3 ways into the evaporator box:
1. As radiant heat from the exhaust manifold.
2. Through conduction from the aluminum evaporator lines into the evaporator itself.
3. Through conduction into the evaporator case as a whole.
Check your water valve, but it's not always the problem.
Here is an experiment I performed to find the cause:
After insuring all a/c system vacuum actuated flappers/doors were operating correctly:
And--after completely disconnecting the heater core from engine coolant--I removed and capped the heater hoses.
Fan Speed on HIGH. Selector set to VENT. Hood seal installed correctly and brand new.
1. I measured temperature coming from the center vent. When engine was cold the thermometer read ambiant outside air temperature.
2. As the engine/engine bay heated up, the temperature slowly rose to 25F above ambiant--causing annoying warm air to enter the cabin.
* Remember, there was no possibility of the heater core being the problem as hoses were completely disconnected.
** I checked to see if air was being sucked from the engine bay into the evaporator fan thus causing the heat. I did this by placing the selector on MAX (recirc), then closing both windows except for a crack at the top of one. Then I blew smoke to see how much air was leaving the cabin. It turned out extrememly little--I have a well sealed system. If it had been sucking engine bay air, it would have pressurized the cabin and forced the air out the through crack.
3. I then put a 8 x 8" x 0.035" sheet of titanium (aluminum would work as well, I just happened to have the piece lying around) between the exhaust manifold and evaporator case. Air temperature slowly dropped 7F.
4. I then put pipe insulation on the aluminum refrigerant lines coming out from the evaporator--this dropped the air temperature another 10F--but much more rapidly.
5. I then covered the entire evaporator case and fan motor with high temperature insulation--from Summit.
Problem solved--ambiant temperature air now coming from the vent (2-3F rise is all that I measured).
Also, now a/c air is much colder at warm startup and 7F colder running.
Conclusion:
Heat is conducted 3 ways into the evaporator box:
1. As radiant heat from the exhaust manifold.
2. Through conduction from the aluminum evaporator lines into the evaporator itself.
3. Through conduction into the evaporator case as a whole.
Check your water valve, but it's not always the problem.
05-27-2007, 01:03 PM
#5
Le Mans Master
Photovette1, GOOD INFO!
Even after sealing my system up as best I could, and installing a ball valve on the heater hose, I still get about 95* heat coming in through the vents, thats even if its only 50-60* outside. If its 85* outside, I still get about the same 95* coming in. I sealed all the holes I could find on the evap box. My AC still manages to cool the system down to 40* or so but....it could always be colder, not to mention when cruising with the tops off and the AC turned off, I could live without the 100* heat coming in.
Even after sealing my system up as best I could, and installing a ball valve on the heater hose, I still get about 95* heat coming in through the vents, thats even if its only 50-60* outside. If its 85* outside, I still get about the same 95* coming in. I sealed all the holes I could find on the evap box. My AC still manages to cool the system down to 40* or so but....it could always be colder, not to mention when cruising with the tops off and the AC turned off, I could live without the 100* heat coming in.
05-27-2007, 08:34 PM
#6
CF JASOC Member
Thread Starter
I had the same problem--the annoying hot air coming from the vents--most noticeable with t-tops off.
Conclusion:
Heat is conducted 3 ways into the evaporator box:
1. As radiant heat from the exhaust manifold.
2. Through conduction from the aluminum evaporator lines into the evaporator itself.
3. Through conduction into the evaporator case as a whole.
Check your water valve, but it's not always the problem.
Conclusion:
Heat is conducted 3 ways into the evaporator box:
1. As radiant heat from the exhaust manifold.
2. Through conduction from the aluminum evaporator lines into the evaporator itself.
3. Through conduction into the evaporator case as a whole.
Check your water valve, but it's not always the problem.
Thanx so much for taking the time to write all this down. It makes perfect sense. The valve is on the way, and I'll be taking your conclusions under advisement from there.
Have a Great Holiday,
xccter
05-28-2007, 08:21 AM
#7
Burning Brakes
John (Photovette1),
Excellent write up! Can you post photos of your evap box after you installed the high temp insulation on it?
The AC evap box is so close to the right hand exhaust manifold that it gets extremely hot from the manifold. I have been strongely considering putting a high temp insulation on my evap box for a long time. My opinion is the same as yours.
Radiant heat is one of the major sources of interior heat in C3's.
Excellent write up! Can you post photos of your evap box after you installed the high temp insulation on it?
The AC evap box is so close to the right hand exhaust manifold that it gets extremely hot from the manifold. I have been strongely considering putting a high temp insulation on my evap box for a long time. My opinion is the same as yours.
Radiant heat is one of the major sources of interior heat in C3's.
05-28-2007, 10:27 AM
#8
CF JASOC Member
Thread Starter
Yes the valve may not be closing and causing a problem. Easy to verify, bypass it. Also the fresh air door may not be closing all the way, mine is hosed up from the factory, with it closed there is a 1/2 inch gap along part of the lip. Have not thought much on how to fix it yet
Is the plenum door vacuum or cable operated?
Not like you can just stick your head under the dash and look at these things. I'm going to try to do it by feel (if there's enough room to do so) if I can get a better idea of what I'm feeling for. After that, the dash comes apart I guess.
Page 15-50 (Air Conditioning) in the '71 GM Service manual has about the best illustrations I can locate, but still not great.
05-28-2007, 10:51 AM
#9
Safety Car
Thanx. I'm trying to figure out where the plenum door and cable/vacuum motor are located to verify that it's closing/opening properly.
Is the plenum door vacuum or cable operated?
Not like you can just stick your head under the dash and look at these things. I'm going to try to do it by feel (if there's enough room to do so) if I can get a better idea of what I'm feeling for. After that, the dash comes apart I guess.
Page 15-50 (Air Conditioning) in the '71 GM Service manual has about the best illustrations I can locate, but still not great.
Is the plenum door vacuum or cable operated?
Not like you can just stick your head under the dash and look at these things. I'm going to try to do it by feel (if there's enough room to do so) if I can get a better idea of what I'm feeling for. After that, the dash comes apart I guess.
Page 15-50 (Air Conditioning) in the '71 GM Service manual has about the best illustrations I can locate, but still not great.
If you remove the fan motor resistor bank, you can see it through the hole.
05-28-2007, 11:11 AM
#10
Le Mans Master
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The plenum door is vac operated. The vac line comes thru the firewall in the big gromet then goes into the wiper tray and to the door operator, follow the hose.
You can also do a search on my name, I put up a thread a few months ago detailing how that stuff all worked with the cront clip off so you can see the parts.
You can also do a search on my name, I put up a thread a few months ago detailing how that stuff all worked with the cront clip off so you can see the parts.
05-28-2007, 03:50 PM
#11
CF JASOC Member
Thread Starter
Sixfooter
I searched for 20 minutes without any luck. If you have the time and can locate the link to it for me, I'd appreciate it.
I searched for 20 minutes without any luck. If you have the time and can locate the link to it for me, I'd appreciate it.
05-28-2007, 08:28 PM
#13
Le Mans Master
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Here is a pic of the plenum area on the pass side, like above you can see the flap and its operator
This in the inboard side of the flap assy
Another angle from above, you can see the vac line running up on the pic thru the wiper tray where it goes thru the wiper tray firewall and loops into the gromet thru the firewall into the cabin
SOmething I found on mine, you can see where the flap touches the firewall, it has worn mine down so that even with the flap closed it would still leak air past it, I think I'll build up the lip on the flap assy to deal with that.
Photo...nice work.
This in the inboard side of the flap assy
Another angle from above, you can see the vac line running up on the pic thru the wiper tray where it goes thru the wiper tray firewall and loops into the gromet thru the firewall into the cabin
SOmething I found on mine, you can see where the flap touches the firewall, it has worn mine down so that even with the flap closed it would still leak air past it, I think I'll build up the lip on the flap assy to deal with that.
Photo...nice work.
05-28-2007, 09:48 PM
#14
CF JASOC Member
Thread Starter
SIXFOOTER & ajrothm:
Those are the exact pics I needed to see. I know the kick panel door and vacuum motor are working perfectly now after disassembling and lubricating all the parts.
Moving up to the plenum flap/vacuum motor and lines in the morning, and replacing the hot water valve when it arrives later in the week.
This Forum can really make a huge difference in owning and maintaining these wonderful cars.
I hope I can or already have returned the favor to someone in the same way on the C3 or C4 side.
Thanx again!
xccter
Those are the exact pics I needed to see. I know the kick panel door and vacuum motor are working perfectly now after disassembling and lubricating all the parts.
Moving up to the plenum flap/vacuum motor and lines in the morning, and replacing the hot water valve when it arrives later in the week.
This Forum can really make a huge difference in owning and maintaining these wonderful cars.
I hope I can or already have returned the favor to someone in the same way on the C3 or C4 side.
Thanx again!
xccter
05-28-2007, 10:20 PM
#15
Le Mans Master
Sixfooter, do you know exactly the order the flaps operate? What I mean is, If you have it on MAX AC, does that mean the kick panel flap should be open and the plenum flap should be shut? I would think by looking at the pics, in order to recirculate cabin air, the kick panel flap would have to be open to let the air from the cabin into the blower, and the plenum flap would have to be shut to keep it from leaking in and out.
The reason I ask is, my kick panel flap has got something funny going on. It stays partially open when the engine is off, when I start it, the valve stays open, when I go to MAX AC, the flap shuts(which is opposite of what I would think it should do) if I go to any other ac setting, the flap stays shut until I shut the engine off. Also I can not verify the plenum flap is doing anything and I can't really figure out how to get to it to seal it shut.
The reason I ask is, my kick panel flap has got something funny going on. It stays partially open when the engine is off, when I start it, the valve stays open, when I go to MAX AC, the flap shuts(which is opposite of what I would think it should do) if I go to any other ac setting, the flap stays shut until I shut the engine off. Also I can not verify the plenum flap is doing anything and I can't really figure out how to get to it to seal it shut.
05-28-2007, 10:50 PM
#16
Le Mans Master
OK after running outside and trying mine again, if I put it on MAX AC , my kick panel flap is like partially open, if I reach in there and pull it back, it easily retracts to the open position. IF I move the selector to NORM, the flap closes tightly, I reached in there and tried to pull it and it hold shut pretty tight. Moving it back to MAX, the flap stays shut but if I reach in there and pull it, I can pull it open pretty easy. That leads me to believe the assy. needs cleaning and lube, maybe a new spring or something.
Then I took out my wiper grate and looked down in the plenum, I can see the plenum flap and it appears to be open. I changed the selector too all posistions and the plenum flap doesn't appear to be moving. The hose is still going to the pod but...who knows. I can reach it with a long screw driver and touch the flap and make it move so I know the hinge isn't froze up.
I guess the default position for the plenum door is open? meaning letting outside air in? By looking at yours and my pics, the doors are open in both pics.
Basically right now, my MAX AC is not getting its full potential because the plenum is stuck open letting outside air in.
Any ideas how to get to the plenum flap?
Gosh what a horrible design.
Then I took out my wiper grate and looked down in the plenum, I can see the plenum flap and it appears to be open. I changed the selector too all posistions and the plenum flap doesn't appear to be moving. The hose is still going to the pod but...who knows. I can reach it with a long screw driver and touch the flap and make it move so I know the hinge isn't froze up.
I guess the default position for the plenum door is open? meaning letting outside air in? By looking at yours and my pics, the doors are open in both pics.
Basically right now, my MAX AC is not getting its full potential because the plenum is stuck open letting outside air in.
Any ideas how to get to the plenum flap?
Gosh what a horrible design.
Last edited by ajrothm; 05-28-2007 at 10:54 PM.
05-29-2007, 09:45 AM
#17
Le Mans Master
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The door is open with engine off and gets vac applied only in MAX ac. You can het to it, but its not easy. Remove the plastic screen on the end of the wiper tray and the safety cable if you have one. Then I think you can get to the mount screws for the back side of the flap.
PITA for sure
PITA for sure
05-29-2007, 05:48 PM
#18
Le Mans Master
I am going to mess with it tonight. From what I can see, both flaps run off of the same vacuum hose. It Ts off to each door, they just pull in opposite directions. I am going to test the vacuum at the kick panel flap vac pod and see if its getting vacuum, if it is, then that means my plenum valve is jacked..If not, then that means my main vacuum hose for that circuit is jacked or the controller has a leak. Either way I gotta fix it.
The 71 manual states that plenum door comes out as an assy, you have to remove the wiper door and all hardware to get it out...THAT I do not want to do.
I gotta get the recirc. working though, maybe I can improve my 42-45* vent temps...
The 71 manual states that plenum door comes out as an assy, you have to remove the wiper door and all hardware to get it out...THAT I do not want to do.
I gotta get the recirc. working though, maybe I can improve my 42-45* vent temps...
05-31-2007, 09:48 AM
#20
CF JASOC Member
Thread Starter
Great stuff on the Tech side. I also am not willing to take the wiper door, etc apart until winter. I lubed all parts on the kick panel vent (PITA) and it is now working. That is, held shut by the spring unless in MAX mode. New hot water valve not here yet, and haven't delved into the plenum door situation yet.
Good Luck, and keep us posted.