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1985 Ford F-150 XLT Lariat 302 EFI w/ Air Conditioning. I only have heat in defrost mode. I was told to check the vacuum lines. All the pots(?) under the dash can be operated manually. While fishing under the dash. I found the bottom control for off AC Max / Normal, vent, floor, mix and defrost has no cable attached to it. I cannot
find the cable. I can't see or feel a lever on the heater box that the cable would attach to. There's one lever on top of the heater box, behind the glove box that the top ****, cool to warm operates. It operates as it should. The on / off under the hood operates as it should. I need a photo or diagram of the lower cable and where it attaches to on the heater box.
DaveF is 100% right as that is how my factory AC is set up.
Now if you out have air blowing out the defrost it can be 1 of 2 things and you will need to do more checking.
It could be the vacuum control is bad and not directing vacuum were it needs to go.
Mine kind of dose that between AC and vent you have to play with it.
The other and most likely the hinge for the door inside the box is broken.
You should have a vacuum motor on the top of the box behind the glove box.
Move the control between AC / floor / defrost. If the control works you should see the motor arm move. If so the hinge is broken.
If the arm dose not move you will need to see if there is vacuum to the motor or not.
No vacuum bad control or no vacuum to the control (yes this can happen dont ask how I know ). Vacuum to motor then bad motor.
Dave ----
Can you please clarify this observation? Are you referring to the temperature of the airflow? Or the destination of the airflow? I THINK you mean the latter, but want to be sure.
As D2 have already mentioned, trucks with factory AC only have a single cable, which operates the hot/cold (temperature control) door. The other doors, which control the airflow destination, are vacuum operated.
These vacuum actuators are spring-loaded in one direction. If there's a problem with the vacuum supply, these actuators automatically position the doors to send all airflow to the defrost outlets. The logic is to keep the windshield clear for safety in the event of a failure with the vacuum supply or control system.
More details about the control system in the beginning of this thread, including how to test it:
Most of that thread covers how to fix the hinge for the door to the vents on the face of the dash. This hinge is a very common failure point, but I don't think your hinge has failed. If it had, most airflow comes out the dash vents, not the defrost.
Can you please clarify this observation? Are you referring to the temperature of the airflow? Or the destination of the airflow? I THINK you mean the latter, but want to be sure.
As D2 have already mentioned, trucks with factory AC only have a single cable, which operates the hot/cold (temperature control) door. The other doors, which control the airflow destination, are vacuum operated.
These vacuum actuators are spring-loaded in one direction. If there's a problem with the vacuum supply, these actuators automatically position the doors to send all airflow to the defrost outlets. The logic is to keep the windshield clear for safety in the event of a failure with the vacuum supply or control system.
More details about the control system in the beginning of this thread, including how to test it:
Most of that thread covers how to fix the hinge for the door to the vents on the face of the dash. This hinge is a very common failure point, but I don't think your hinge has failed. If it had, most airflow comes out the dash vents, not the defrost.
Or the destination of the airflow? I THINK you mean the latter, but want to be sure, yes destination of the air flow. At least I now know there is no cable. I'll have to get a vacuum gauge and start testing. That you for all the help. I was questioning the vacuum manifold on the right side of the controller. Any idea why it has an open port? Vent?
I'll have to get a vacuum gauge and start testing. That you for all the help. I was questioning the vacuum manifold on the right side of the controller. Any idea why it has an open port? Vent?
IIRC, not all ports on the back of the controller are used. Judging by the picture, there don't appear to be any marks from a hose having been previously installed. You may find some of those ports have closed ends, and were never drilled out.
I'd suggest tracing out the hoses and finding which one is the vacuum supply from the engine. Look under the hood for the vacuum reservoir. It's located between the battery and heater fan motor. It looks like either a plastic cannonball or a metal tomato can, depending on the year. Next to this reservoir is a small check valve with 3 hoses. One goes to the engine, another to the vacuum reservoir, and the third to the HVAC controller. You can see these components in the top left corner of the diagram in post #2 above. With the engine at idle, you should have a strong vacuum present on the line to the controller. Make sure that is present before digging deeper.
If you have the metal reservoir, look underneath. They are notorious for rusting out at the bottom and causing a vacuum leak. That could reduce the vacuum available to the controller.
IIRC, not all ports on the back of the controller are used. Judging by the picture, there don't appear to be any marks from a hose having been previously installed. You may find some of those ports have closed ends, and were never drilled out.
I'd suggest tracing out the hoses and finding which one is the vacuum supply from the engine. Look under the hood for the vacuum reservoir. It's located between the battery and heater fan motor. It looks like either a plastic cannonball or a metal tomato can, depending on the year. Next to this reservoir is a small check valve with 3 hoses. One goes to the engine, another to the vacuum reservoir, and the third to the HVAC controller. You can see these components in the top left corner of the diagram in post #2 above. With the engine at idle, you should have a strong vacuum present on the line to the controller. Make sure that is present before digging deeper.
If you have the metal reservoir, look underneath. They are notorious for rusting out at the bottom and causing a vacuum leak. That could reduce the vacuum available to the controller.
Thanks, I have vacuum to the actuator.in the engine bay that open & closes the door to stop air into the cab. Reservoir is plastic. Thanks for your help!
So the arm on the vacuum motor moves but the air flow dose not change where ti is going to?
If you were checking vacuum in the engine bay to the fire wall and have vacuum to that point great but you need to check for vacuum inside the cab.
I have had vacuum to the fire wall but not make it inside the cab. The vacuum line broke inside that rubber pass thru part so have vacuum on the motor side but not inside.
With that said you need to make sure vacuum is at the control and then to the vacuum motors.
Dave ----
So the arm on the vacuum motor moves but the air flow dose not change where ti is going to?
If you were checking vacuum in the engine bay to the fire wall and have vacuum to that point great but you need to check for vacuum inside the cab.
I have had vacuum to the fire wall but not make it inside the cab. The vacuum line broke inside that rubber pass thru part so have vacuum on the motor side but not inside.
With that said you need to make sure vacuum is at the control and then to the vacuum motors.
Dave ----
I found the issue. the vacuum manifold, (?), on the climate control panel is cracked.
Good find
Wonder if that is why mine dose not switch with out moving the lever?
It also looks like that PN will work for me as I have the later panel installed in my 81 F100 as there are 2 different panels.
IIRC the vent & floor or something like that are in different places.
Will try and find it cheaper than the $100 that I first found with that part number
Dave ----
). Vacuum to motor then bad motor.
