Vent question not AC

[Alex Brooks]

Ok so my mode switch works. ac works and blows cold.
But went I just want to bring in out side with the vent set to cold hot air still comes out of the vents in the car.

I check to see if the heater control valve close and it does close on max ac.
Is my temp control knob dead ?

[CriticalB]

Is your blend door opening/closing when you adjust the temp knob? you might be able to see if the door is actuating from the passenger footwell. Even if the heater core isn't getting hot, maybe the air is still bypassing the evaporator.

[eight8toy]

I just tore apart my HVAC to replace my evaporator and I don't think the air ever bypasses the evap to my knowledge. Would just blow past it on its way to the heater core for hot air. Someone correct me if I'm wrong though.

I would agree your blend door may not be working properly with the temp control knob. Should be able to hear it move back and forth in the passenger foot well when adjusting it. To be honest, before I fixed my AC, even when I had the cold temp set to vent, the air still came through fairly warm, at least warmer than outside temps. Man the car was miserable to drive when it was hot out!

[dn010]

I just tore apart my HVAC to replace my evaporator and I don't think the air ever bypasses the evap to my knowledge. Would just blow past it on its way to the heater core for hot air. Someone correct me if I'm wrong though.

I would agree your blend door may not be working properly with the temp control knob. Should be able to hear it move back and forth in the passenger foot well when adjusting it. To be honest, before I fixed my AC, even when I had the cold temp set to vent, the air still came through fairly warm, at least warmer than outside temps. Man the car was miserable to drive when it was hot out!

+1. Check the cable to the blend flap.

[Alex Brooks]

+1. Check the cable to the blend flap.

Ok I will check that today are the blend motors vaccum powered ?
Thank you for the replies.

[dn010]

The door that is controlled by the temp knob uses a cable. The rest are vacuum.

[Alex Brooks]

The door that is controlled by the temp knob uses a cable. The rest are vacuum.

So I should be able to hear it move with the car running ?

[dn010]

If you're asking about the temp knob I think it would be difficult to tell if the cable is actually working without looking at the ends and making sure it's connected and moving - you won't hear the actual door, you might notice a difference in air sound from full hot to full cold though when the fan is running. If you use the mode switch you should hear things opening and closing. There are not that many things to check and most can be seen just by looking under the dash. My control cable is light blue in color so it is easy to identify, I'm not sure if all original cables are like that or not but if so, that is what you're looking for as far as the temp control issue.

[eight8toy]

Mine was light blue as well.

Make sure to turn the engine on just to build vacuum in the system so all the doors and stuff are "charged". The blend door won't need vacuum though to work...

I would think you would be able to hear faintly the door moving when you adjust the temp control knob but your ear would have to be right next to the HVAC box I guess. The knob would probably be much easier to twist if the cable is indeed not connected anymore. Is your temp knob turning freely or do you feel some normal resistance while adjusting it?

[Alex Brooks]

Mine was light blue as well.

Make sure to turn the engine on just to build vacuum in the system so all the doors and stuff are "charged". The blend door won't need vacuum though to work...

I would think you would be able to hear faintly the door moving when you adjust the temp control knob but your ear would have to be right next to the HVAC box I guess. The knob would probably be much easier to twist if the cable is indeed not connected anymore. Is your temp knob turning freely or do you feel some normal resistance while adjusting it?

The knob I feel is somewhat hard to turn but I can hear it moving something. Mine is also light blue. I’m quite perplexed why I keep getting warm air. It if I turn the air on the air gets cold. But like this morning it’s 50 degrees I would like to just bring in some fresh air.

[eight8toy]

So if the blend door appears to be working then your mode switch might be the problem? Maybe one of the little vacuum lines got disconnected or has rotted out? I know I just pulled my radio and while doing so the wires caught that octopus contraption and pulled it off so I had to reattach everything. You done any radio or other work in that area recently?

When you turn the engine on and then from the OFF position attempt to switch it to VENT do you hear anything back there snap open/close?

If all else fails you can do what I used to do and even with the fan blowing air in I basically had to drive like Ace Ventura with my head pressed against the toll window opening to catch any fresh air since it was hot all the time!

57971

[SS Spoiler]

Only if your Jim Reeves [he is tiny enough to
climb through his window!]

[Alex Brooks]

So if the blend door appears to be working then your mode switch might be the problem? Maybe one of the little vacuum lines got disconnected or has rotted out? I know I just pulled my radio and while doing so the wires caught that octopus contraption and pulled it off so I had to reattach everything. You done any radio or other work in that area recently?

When you turn the engine on and then from the OFF position attempt to switch it to VENT do you hear anything back there snap open/close?

If all else fails you can do what I used to do and even with the fan blowing air in I basically had to drive like Ace Ventura with my head pressed against the toll window opening to catch any fresh air since it was hot all the time!

57971

I have not had any radio work done at all. so no one was messing around in there I will go check the mode switch right now. just seem weird that I can cold AC but no vent.

[dn010]

I'd still go by sight and not sound. If room allows, position your cellphone recording video at the cable end and move the switch to confirm. Even better is if you can remove the cable end and test the flap by hand. If no work has been done on your hvac box then you'll also have flaps on which the foam has long disintegrated and is now missing and not fully sealing.

[Alex Brooks]

I'd still go by sight and not sound. If room allows, position your cellphone recording video at the cable end and move the switch to confirm. Even better is if you can remove the cable end and test the flap by hand. If no work has been done on your hvac box then you'll also have flaps on which the foam has long disintegrated and is now missing and not fully sealing.

I’m on drive right now in the car an it all is working normal now I guess it is a DeLorean miracle.
Thank you all for your help
Will check for foam blocking it. When I get home.
I had not drove the car for about a month until yesterday.

Any ideas what would cause it to be an intermittent problem if this returns

[CriticalB]

I have not had any radio work done at all. so no one was messing around in there I will go check the mode switch right now. just seem weird that I can cold AC but no vent.

If the mode switch is on vent, the recirculation door should be closed, which its default position on anything except max AC. When this door is closed, fresh air is pulled across an ambient-temp evaporator directly to the floor and face vents. According to the workshop manual, the heater valve only closes on max ac, so the heater core will be hot. If the blend door (controlled by the temp control knob) is set to full cold, the heater core should be completely bypassed. The other likely place heat could escape is if the foam on the back of the heater box is loose or missing, but you would feel that warm air in the driver footwell rather than from the face vents.

I'm thinking it has to be something with the blend door. The heater core is always hot except on Max AC, and even if your recirc door was somehow stuck open, it still mixes enough fresh air with the cabin air that it shouldn't feel hot - as long as the blend door is fully closed.

[hippieman9]

I have not had any radio work done at all. so no one was messing around in there I will go check the mode switch right now. just seem weird that I can cold AC but no vent.

If you're not the original owner you never know what the PO did or didn't do. I found my vacuum lines in the wrong places and the T connector for the hot water valve/ recirc was disconnected.
There is a diagram in the Technical manual that shows where each line should go.