Heater Recirc Door
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Cargo Master
Joined: May 2004
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Heater Recirc Door
When the 1990 Bronco is running and the heater is off the vacuum closes the door that lets outside air into the heater system. The door closes so that the blower, if it was on, would get air from inside the cab.
When the heater is turned on this vacuum is turned off so that outside air is sucked into the heater system to be heated by the heater core then sent into the cab.
How has anyone else rectified this so that the door can be set to recirculate cabin air instead of sucking -10 degree air from outside.
I have the vacuum motor tied in the closed position with a small piece of cord. I think a zip tie would work also. A better solution would be a switch that would apply vacuum when desired. Mercedes Benz has a switch that does something similar, I'm not sure if it applies vacuum.
Any Ideas out there?
When the heater is turned on this vacuum is turned off so that outside air is sucked into the heater system to be heated by the heater core then sent into the cab.
How has anyone else rectified this so that the door can be set to recirculate cabin air instead of sucking -10 degree air from outside.
I have the vacuum motor tied in the closed position with a small piece of cord. I think a zip tie would work also. A better solution would be a switch that would apply vacuum when desired. Mercedes Benz has a switch that does something similar, I'm not sure if it applies vacuum.
Any Ideas out there?
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Cargo Master
Joined: May 2004
Posts: 3,007
Likes: 5
Now that I've read some more in my 1990 Bronco Service Manual, I've found that the AC does operate in the AC (Max and Norm), Floor/Defrost, and Defrost positions. It's shut off in the Off, Vent, Floor positions.
Posting Guru
Joined: Apr 2006
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You correct about A/C operation. But you origenal question concerned the inlet door. In the norm position the door is open. So thats no help. I'm not sure about the door when in defrost, but I believe its also open. I could be wrong, but I believe the only times that the door is closed is Off and Max A/C.
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Cargo Master
Joined: May 2004
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Well, I'm going to do an experiment tomorrow.
I'll test which condition is best to get the highest temperature air out of the vents.
The three conditions are
1. Max A/C,
2. Vent with the truck set up as designed, i.e. no modification of the outside air vent control, and
3. Vent with the outside door tied shut by modification.
The air temp will be set to max heat in all three of these conditions. I'm using vent because it lessens one variable, that variable being the cabin outlet of the heated air.
My hypothesis is that the modified Vent conditon (3) will produce the highest air temp out of the vents. Followed by the Max AC condition (1), and finally the Vent condition (2) with outside air being heated.
I'll post results tomorrow afternoon.
I'll test which condition is best to get the highest temperature air out of the vents.
The three conditions are
1. Max A/C,
2. Vent with the truck set up as designed, i.e. no modification of the outside air vent control, and
3. Vent with the outside door tied shut by modification.
The air temp will be set to max heat in all three of these conditions. I'm using vent because it lessens one variable, that variable being the cabin outlet of the heated air.
My hypothesis is that the modified Vent conditon (3) will produce the highest air temp out of the vents. Followed by the Max AC condition (1), and finally the Vent condition (2) with outside air being heated.
I'll post results tomorrow afternoon.
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Cargo Master
Joined: May 2004
Posts: 3,007
Likes: 5
Ok, here's the results:
The outside temp in Montana this morning is 20 degrees F
The truck is fully warmed up.
The inside truck Temp is 40 degrees F
The temp of air coming out of the vent at Max AC was 104
The temp of air coming out of the vent at Vent was 103
The temp of air coming out of the vent at Vent M was 103.
Conclusion, it's too cold to be running experiments in Montana and the heat is plenty coming out of the vents.
The outside temp in Montana this morning is 20 degrees F
The truck is fully warmed up.
The inside truck Temp is 40 degrees F
The temp of air coming out of the vent at Max AC was 104
The temp of air coming out of the vent at Vent was 103
The temp of air coming out of the vent at Vent M was 103.
Conclusion, it's too cold to be running experiments in Montana and the heat is plenty coming out of the vents.
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