Heater

[my70chevyc10]

My heater isnt working and i have changed the switch,resistor,fuse and motor. There is power going to the fuse box and across the fuse but not to the switch. someone said there was a relay between the use block and the switch. I have looked on the wiring diagram and didnt see any relay. Please help.

[raycow]

Unless you are doing a stock resto for points, just cheat. Run a jumper from the fuse block to the switch. Nobody but you will ever know.

Ray

[RustyParts]

First thing I would do is check the blower motor, unplug the harness at the firewall in the engine compartment and connect one end of a jumper wire to the heater motor lead and touch the other end to the positive battery post. This way bypasses the rest of the circuit.

The motor should run, if it doesn't check to make sure the ground wire for the heater motor is clean and has a good connection. If it still doesn't run chances are the motor is bad or the fan is caught on something.

If the heater motor runs the next item working backwards is the resistor. The blower speeds are regulated here by changing the resistance going to the blower. Low and medium speeds are controlled by resistance and high speed is not. Yellow and blue wires are low and medium and orange is fed straight to the blower.

The other device that completes the circuit is the switch on the heater control panel.

To check the circuit I would use a test light. Make sure it works before using,...that's another story.
Turn the ignition switch to the "On" position and check the brown wire at the heater switch. If it lights up you have power at the switch, If it doesn't there is a problem with this wire going back to the fuse panel ie. cut.

If you have power at the brown wire, place the test light on either the Yellow or blue wire and move the blower speed lever to low or medium speed the light should come on as you move the lever. Do the same for the other wire.

Move the fan speed lever to high and check the Orange wire it should light up. If you have power at the brown wire and no power to any of the others, the switch is bad.

If you have power to all the connections at the heater switch the only other thing left is the resistor you will have to check for power at the resistor using the previous method. If you have power to all the connections here and the blower is still not running, the blower motor is bad or the wire going to it is open or has a bad connection.

Long post but hopefully it helps you solve your problem. Good Luck.

[mightyatom]

Great post RustyParts. I also have the same issue so will be going through this sequence next weekends. I was just going to wing it but thought I would search the forum and got this thread first time. This will save a lot of wasted time I am sure. Maybe a good one to add in the FAQ section.

Anyways, many thanks for the details.

[68C10HotRod]

RustyParts said to use a test light & that is very important. I replaced a couple motors just because I used a meter & had continuity & volts through all the connections but one of the wires (brown) is broke just bad enough to not allow any current to flow across it. Probably would have found it right off if I would have used a test light but didn't have one at the time. A buddy thought this motor was bad too but when I said "the 3rd one!" he said, let's jumper power straight to it & see if it works then - sure did.