HVAC Control help needed
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Laughing Gas
Joined: Aug 2004
Posts: 856
Likes: 270
From: SoCal
HVAC Control help needed
I just picked up this truck and have found my first undisclosed problem. The A/C only works on MAX. If you turn the **** to any other setting, regardless of selected temp, the air blows hot. And I mean full hot! I was thinking the control panel assembly is bad?
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,078
From: St Louis
Do NOT screw with the vacuum lines, they are not the issue. It is a blend door that is not operating properly. The blend door is electrically operated, it is not operated by vacuum. Might be as simple as a stripped temperature control **** on the control panel.
The reason you get proper air conditioning in MAX is that the vacuum-operated coolant valve in the heater core loop is shutting off the coolant flow to the core in the MAX position so there is no re-heating of the conditioned air.
The reason you get proper air conditioning in MAX is that the vacuum-operated coolant valve in the heater core loop is shutting off the coolant flow to the core in the MAX position so there is no re-heating of the conditioned air.
Thread Starter
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Laughing Gas
Joined: Aug 2004
Posts: 856
Likes: 270
From: SoCal
Do NOT screw with the vacuum lines, they are not the issue. It is a blend door that is not operating properly. The blend door is electrically operated, it is not operated by vacuum. Might be as simple as a stripped temperature control **** on the control panel.
The reason you get proper air conditioning in MAX is that the vacuum-operated coolant valve in the heater core loop is shutting off the coolant flow to the core in the MAX position so there is no re-heating of the conditioned air.
The reason you get proper air conditioning in MAX is that the vacuum-operated coolant valve in the heater core loop is shutting off the coolant flow to the core in the MAX position so there is no re-heating of the conditioned air.
Fleet Mechanic
Joined: Nov 2011
Posts: 1,825
Likes: 43
From: Land of Taxes
This applies to newer trucks say 07-13s or 14s. Not real sure on all the design changed from 04 up to 08 or 13-15.
This is general info for HVAC. So no temp control or blower motor control sounds like two things. The blower motor resistor PCB and the blend door. Not sure where either are located on an 04.
A bad blend door will fluctuate temp while driving and/or will exhibit a large hysteresis when you adjust temp a little bit. Or wont respond at all like yours.
A vacuum control problem usually shows up as only the defrosters will blow any air, that's the default with a vacuum leak in that circuit. Which is usually caused by a bad/leaking vac hose down on the front axle on the ESOF auto locking 4WD hub option.
This is general info for HVAC. So no temp control or blower motor control sounds like two things. The blower motor resistor PCB and the blend door. Not sure where either are located on an 04.
A bad blend door will fluctuate temp while driving and/or will exhibit a large hysteresis when you adjust temp a little bit. Or wont respond at all like yours.
A vacuum control problem usually shows up as only the defrosters will blow any air, that's the default with a vacuum leak in that circuit. Which is usually caused by a bad/leaking vac hose down on the front axle on the ESOF auto locking 4WD hub option.
Hotshot
Joined: Jan 2004
Posts: 19,760
Likes: 1,078
From: St Louis
I'm "guessing" you're working on the 04, you never specifically identified your project.
If so, it's fairly easy to drop the glove box door out and to get to the blend door actuator in top of the plenum. Pop it off, and exercise the temp **** and see if the actuator shaft moves correctly in relation to the ****'s positioning.
I had a very similar problem with my 01 last fall but it was intermittent. I finally found a cold solder joint on the circuit board inside the actuator that, once it was re-flowed, has worked correctly since then.
If so, it's fairly easy to drop the glove box door out and to get to the blend door actuator in top of the plenum. Pop it off, and exercise the temp **** and see if the actuator shaft moves correctly in relation to the ****'s positioning.
I had a very similar problem with my 01 last fall but it was intermittent. I finally found a cold solder joint on the circuit board inside the actuator that, once it was re-flowed, has worked correctly since then.
Thread Starter
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Laughing Gas
Joined: Aug 2004
Posts: 856
Likes: 270
From: SoCal
I'm "guessing" you're working on the 04, you never specifically identified your project.
If so, it's fairly easy to drop the glove box door out and to get to the blend door actuator in top of the plenum. Pop it off, and exercise the temp **** and see if the actuator shaft moves correctly in relation to the ****'s positioning.
I had a very similar problem with my 01 last fall but it was intermittent. I finally found a cold solder joint on the circuit board inside the actuator that, once it was re-flowed, has worked correctly since then.
If so, it's fairly easy to drop the glove box door out and to get to the blend door actuator in top of the plenum. Pop it off, and exercise the temp **** and see if the actuator shaft moves correctly in relation to the ****'s positioning.
I had a very similar problem with my 01 last fall but it was intermittent. I finally found a cold solder joint on the circuit board inside the actuator that, once it was re-flowed, has worked correctly since then.
I will check the blend door as you suggest - thank you!
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