heat control
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Mountain Pass
Joined: Jan 2003
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heat control
I bought a used 1998 Explorer today that has a heater issue. The **** to control the temperature (the middle **** on the dash) apparently does nothing. The temperature of the air varies from one exteme to the next without the **** moving. The good news is I used that to get a better price on the rig.
I pulled the radio so I could see the back of the switch and found that it's electrical, not a mechanical link as I am used to. I unplugged and plugged the wires from the switch several times and didn't fix anything (I was hoping for a poor connection.)
My question to anyone with experience/ideas is this a problem in the rotary **** or is it elsewhere in the system? I'm guessing the answer could be both, how do I test the **** to see if the problem lies there or somewhere else?
Any help is greatly appreciated, Brian
I pulled the radio so I could see the back of the switch and found that it's electrical, not a mechanical link as I am used to. I unplugged and plugged the wires from the switch several times and didn't fix anything (I was hoping for a poor connection.)
My question to anyone with experience/ideas is this a problem in the rotary **** or is it elsewhere in the system? I'm guessing the answer could be both, how do I test the **** to see if the problem lies there or somewhere else?
Any help is greatly appreciated, Brian
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Joined: Jan 2001
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From: Virginia
I am looking at a 99 Explorer wiring diagram.
First, check fuse #10, 7.5 amp in the fuse box.
The control is just a potientometer like a volume control on a radio. It has three terminals. Get an ohmmeter and check the resistance between the terminals where the yellow/lightgreen and the grey red are. You should get some sort of constant resistance, though I am not sure what it should be. Then while leaving one meter lead on one of the above wires, move the other lead to the darkgreen/orange terminal. When you turn the ****, you should see the resistance value sweep up and down smoothly from zero to the first value you got in the first test.
The only other thing in the system is the unit at the blend door. Apparently the electronics and the actuator are all built together at the temp blend door. The only other connection you could check is a ground that it shows hooked to the actuator unit at the door.
First, check fuse #10, 7.5 amp in the fuse box.
The control is just a potientometer like a volume control on a radio. It has three terminals. Get an ohmmeter and check the resistance between the terminals where the yellow/lightgreen and the grey red are. You should get some sort of constant resistance, though I am not sure what it should be. Then while leaving one meter lead on one of the above wires, move the other lead to the darkgreen/orange terminal. When you turn the ****, you should see the resistance value sweep up and down smoothly from zero to the first value you got in the first test.
The only other thing in the system is the unit at the blend door. Apparently the electronics and the actuator are all built together at the temp blend door. The only other connection you could check is a ground that it shows hooked to the actuator unit at the door.
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Mountain Pass
Joined: Jan 2003
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Thanks, the switch tests out OK.
Is the blend door the one right behind the glove box? I removed the glove box and found a door that opens and closes, when open I can see the fan motor. Judging by where the heater hoses go through the firewall, it's in the right area to be just below the heater core. The actuator at the bottom is vacuum, I removed it and tested it by pushing the plunger in and holding my finger over the end. It held until I removed my finger from the hole and it popped back to it's original position. I can't seem to see where the vacuum lines go. I'm going back out to work on it some more right now.
Thanks again for the help, now I've at least narrowed it down a little bit.
Is the blend door the one right behind the glove box? I removed the glove box and found a door that opens and closes, when open I can see the fan motor. Judging by where the heater hoses go through the firewall, it's in the right area to be just below the heater core. The actuator at the bottom is vacuum, I removed it and tested it by pushing the plunger in and holding my finger over the end. It held until I removed my finger from the hole and it popped back to it's original position. I can't seem to see where the vacuum lines go. I'm going back out to work on it some more right now.
Thanks again for the help, now I've at least narrowed it down a little bit.
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Joined: Jan 2001
Posts: 57,025
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From: Virginia
Here is a nice flow diagram. But it is a cable system. If they just upgraded the control system to electronic, but kept the overall layout, this diagram may help you.
http://www.autozone.com/images/cds/g...3d800b9b6d.gif
http://www.autozone.com/images/cds/g...3d800b9b6d.gif
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