Lost two of three heater speeds on my truck, which has the Heavy Duty heater option.
If YOU are having problems, first things first, you need to check the wires going to the heater box to see if they have power when you have the switch in the right positions. Each wire should have 12V at some point in the switches travel. If one or more do not, the problem is "upstream", next stop heater switch. You need to make sure the brown wire is providing 12V to the switch. If it is, the switch is faulty, or the wiring between the heater switch and heater box is. If it is not providing 12V, something before the heater switch is the problem. With 12V at the brown wire, you can CAREFULLY use a small wire and connect the brown wire to the other three wires in the plug to make sure the fan operates with 12V to each one. If they do, the switch is definitely the problem. If they don't, the problem is at the heater box, or the wire(s), to it. Remember that the ignition switch needs to be on to test, and that means you can leave the battery connected for this work, as long as the key isn't in "run". So you can listen to your radio while doing this.
You can use a continuity tester before disassembling the switch if you like, instead of jumpering the wiring in the plug. If the top terminal doesn't have continuity with the corresponding "out" terminal when the switch is in the right position, you've got a switch problem.
Really didn't want to try and rip the actual switch all the way out, since the knob is a "one time" fit. It uses barbs to retain it, which dig into the chromed plastic knob. Disassembly can result in broken pieces, or a loose knob on the switch.
Decided to take the switch apart, see what makes it tick. For reference, the HD heater switch is setup with the bottom position as "off", then low, medium, and high. I am unsure about non-HD heater setups and AC switches, all switches are probably the same actually. (HD heater and AC use the same fan, non-AC/HD trucks use a weaker fan motor) This is at least for the '81+ trucks, earlier trucks (and some later?) had the fan running all the time for ventilation. This setup does not.
The top terminal on the switch/switch plug is the 12V feed from the fuse panel. Moving the switch up or down changes which other wire in the switch plug gets 12V, which then goes to the corresponding resistor mounted on the heater box. Easy...3 total wires go to the heater box from the heater siwtch plug...one is straight 12V to the fan for high, the other two go through resistors to cut the voltage down to the fan.
In any event, heres what you do to disassemble the switch, I'm not going to talk about getting the dash bezel or anything else off, that's a given. The switch pieces all fit together only one way, so no worries there! Except the copper plate, but I detail that below.
Unbolt the heater head from the dash. 4 sheet metal screws. Probably want to disconnect the control wires to the heater box so you can more easily move the control head. Everything is mounted to plastic which can and will break with enough force. Remove the switch plug. It has locking tabs on both sides, so pull those apart and push back on the plug.
Find the screw on the passenger side of the switch, on the backside of the control head. Remove.
On the same side of the switch, locate the white locking tabs. You can see one of the two locking tabs here:
The other tab is in the same cavity, just up a bit higher so you can't see it. To unlock that piece, you need a SMALL flat blade screwdriver. You won't have much luck using needle nose pliers, you need to unlock one side at a time. Turn the switch/heater head so the locking tabs are facing up.
Unlock the tabs, and the white piece will fall off the other side. The white piece is what "clicks" and sets the position for the lever on each fan speed. This is the "drivers side" of the switch, with the other side of the white plastic piece shown here:
You can see the grooves in the brown/black plastic piece (which is the part the lever is attached to) that are the switch detents. The white plastic piece has teeth that ride in those for the speed settings.
When the white piece pops free, the orange plastic piece and brown plastic piece will seperate. There are three springs in cups in the brown plastic piece, with a copper plate over the top of them. Don't lose these pieces, they are not retained once the white piece pops free. The below and above picture are the same piece, different sides. Here, two of the springs are removed, as is the copper plate:
Note that the black/brown piece stays in the heater head at all time, since the lever goes through the front of the heater head. Also that the three spring pockets are NOT equidistant. This means the copper plate will only fit one way with the springs seated correctly. Also there are two alignment tabs in the plastic, and two corresponding slots on the outer edge of the copper plate. Again, this helps assembly, since the copper plate can't rotate when depressed against the springs.
Here is what the copper plate looks like, and the orange piece, which is where the magic happens:
You'll want to check for cracks in the copper here, you can use a continuity tester if you've got one.
Note that the springs fit into the depressions on the back of the copper piece, not this side. As you can see on the orange piece, the far right terminal has melted the plastic. This is the 12V feed from the fuse panel. The springs provide the force that keeps the copper piece against the contacts, but in my case, the bubbled up plastic pushed the copper plate away from the terminals, meaning lost fan speeds. I trimmed that plastic down to where it should be, problem solved. This fix is not going to last forever, as the copper terminal has receeded into the plastic...eventually it will receed further and lose contact with the plate. I first cleaned all the contacts, used dielectric grease, and re-tested to try and fix, but the problem was the plastic. Problem probably occurred BECAUSE of the corrosion/crud generating heat, but too late now to change that.
Assembly is the reverse. It's not difficult at all to get the two halves together, even with the springs and copper plate. It's not a real precise fit, so it goes together easy.
Probably not many out there that will use this, but it's certainly the cheapest fix out there, which can't make things worse if your heater switch is defective already. Since all but the lever piece is seperate, a wrecking yard piece can be swapped in, as long as it's any piece OTHER than the brown plastic piece with the lever.
Please let me know if there is anything unclear in this...I can't take more pics since I reassembled it, but I can describe more if necessary.
Update: Heater switches aren't all the same. Pulled a switch out of a 1989 cab/chassis truck, and noticed that the heater switch uses a spring/detent ball for the speed selector settings, unlike the one pictured above. The 1989 switch was missing the ball, so I'm going to call it an inferior design (more parts), but that's just my opinion. I noticed that similar vintage cars used the detent ball switch as well, so it may have been a perceived "comfort" thing, in being an easier to manipulate switch. Orange plastic contact plate is the same however, as is the copper piece that moves and conducts the current.
If YOU are having problems, first things first, you need to check the wires going to the heater box to see if they have power when you have the switch in the right positions. Each wire should have 12V at some point in the switches travel. If one or more do not, the problem is "upstream", next stop heater switch. You need to make sure the brown wire is providing 12V to the switch. If it is, the switch is faulty, or the wiring between the heater switch and heater box is. If it is not providing 12V, something before the heater switch is the problem. With 12V at the brown wire, you can CAREFULLY use a small wire and connect the brown wire to the other three wires in the plug to make sure the fan operates with 12V to each one. If they do, the switch is definitely the problem. If they don't, the problem is at the heater box, or the wire(s), to it. Remember that the ignition switch needs to be on to test, and that means you can leave the battery connected for this work, as long as the key isn't in "run". So you can listen to your radio while doing this.
You can use a continuity tester before disassembling the switch if you like, instead of jumpering the wiring in the plug. If the top terminal doesn't have continuity with the corresponding "out" terminal when the switch is in the right position, you've got a switch problem.Really didn't want to try and rip the actual switch all the way out, since the knob is a "one time" fit. It uses barbs to retain it, which dig into the chromed plastic knob. Disassembly can result in broken pieces, or a loose knob on the switch.
Decided to take the switch apart, see what makes it tick. For reference, the HD heater switch is setup with the bottom position as "off", then low, medium, and high. I am unsure about non-HD heater setups and AC switches, all switches are probably the same actually. (HD heater and AC use the same fan, non-AC/HD trucks use a weaker fan motor) This is at least for the '81+ trucks, earlier trucks (and some later?) had the fan running all the time for ventilation. This setup does not.
The top terminal on the switch/switch plug is the 12V feed from the fuse panel. Moving the switch up or down changes which other wire in the switch plug gets 12V, which then goes to the corresponding resistor mounted on the heater box. Easy...3 total wires go to the heater box from the heater siwtch plug...one is straight 12V to the fan for high, the other two go through resistors to cut the voltage down to the fan.
In any event, heres what you do to disassemble the switch, I'm not going to talk about getting the dash bezel or anything else off, that's a given. The switch pieces all fit together only one way, so no worries there! Except the copper plate, but I detail that below.
Unbolt the heater head from the dash. 4 sheet metal screws. Probably want to disconnect the control wires to the heater box so you can more easily move the control head. Everything is mounted to plastic which can and will break with enough force. Remove the switch plug. It has locking tabs on both sides, so pull those apart and push back on the plug.
Find the screw on the passenger side of the switch, on the backside of the control head. Remove.
On the same side of the switch, locate the white locking tabs. You can see one of the two locking tabs here:
The other tab is in the same cavity, just up a bit higher so you can't see it. To unlock that piece, you need a SMALL flat blade screwdriver. You won't have much luck using needle nose pliers, you need to unlock one side at a time. Turn the switch/heater head so the locking tabs are facing up.
Unlock the tabs, and the white piece will fall off the other side. The white piece is what "clicks" and sets the position for the lever on each fan speed. This is the "drivers side" of the switch, with the other side of the white plastic piece shown here:
You can see the grooves in the brown/black plastic piece (which is the part the lever is attached to) that are the switch detents. The white plastic piece has teeth that ride in those for the speed settings.
When the white piece pops free, the orange plastic piece and brown plastic piece will seperate. There are three springs in cups in the brown plastic piece, with a copper plate over the top of them. Don't lose these pieces, they are not retained once the white piece pops free. The below and above picture are the same piece, different sides. Here, two of the springs are removed, as is the copper plate:
Note that the black/brown piece stays in the heater head at all time, since the lever goes through the front of the heater head. Also that the three spring pockets are NOT equidistant. This means the copper plate will only fit one way with the springs seated correctly. Also there are two alignment tabs in the plastic, and two corresponding slots on the outer edge of the copper plate. Again, this helps assembly, since the copper plate can't rotate when depressed against the springs.
Here is what the copper plate looks like, and the orange piece, which is where the magic happens:
You'll want to check for cracks in the copper here, you can use a continuity tester if you've got one.
Note that the springs fit into the depressions on the back of the copper piece, not this side. As you can see on the orange piece, the far right terminal has melted the plastic. This is the 12V feed from the fuse panel. The springs provide the force that keeps the copper piece against the contacts, but in my case, the bubbled up plastic pushed the copper plate away from the terminals, meaning lost fan speeds. I trimmed that plastic down to where it should be, problem solved. This fix is not going to last forever, as the copper terminal has receeded into the plastic...eventually it will receed further and lose contact with the plate. I first cleaned all the contacts, used dielectric grease, and re-tested to try and fix, but the problem was the plastic. Problem probably occurred BECAUSE of the corrosion/crud generating heat, but too late now to change that.
Assembly is the reverse. It's not difficult at all to get the two halves together, even with the springs and copper plate. It's not a real precise fit, so it goes together easy.
Probably not many out there that will use this, but it's certainly the cheapest fix out there, which can't make things worse if your heater switch is defective already. Since all but the lever piece is seperate, a wrecking yard piece can be swapped in, as long as it's any piece OTHER than the brown plastic piece with the lever.
Please let me know if there is anything unclear in this...I can't take more pics since I reassembled it, but I can describe more if necessary.
Update: Heater switches aren't all the same. Pulled a switch out of a 1989 cab/chassis truck, and noticed that the heater switch uses a spring/detent ball for the speed selector settings, unlike the one pictured above. The 1989 switch was missing the ball, so I'm going to call it an inferior design (more parts), but that's just my opinion. I noticed that similar vintage cars used the detent ball switch as well, so it may have been a perceived "comfort" thing, in being an easier to manipulate switch. Orange plastic contact plate is the same however, as is the copper piece that moves and conducts the current.
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