Thomas Simcich

1966 442, heater only blows at one speed, not matter what speed is selected. What could be wrong?

Olds64

It could be the resitstor in your air plenum. I've had to replace theis before to get the fan working correctly. I'm not sure if this is a part that is reporduced. When I got mine I had to go to the salvage yard.

MDchanic

Which speed, and is it in ALL positions, or are there some with no fan?

- Eric

Thomas Simcich

It seems to be in all positions!

MDchanic

Hmmm...

Yours is a '66. I'm not sure when the high fan relay was introduced, but you may have a system without one. If that's the case, it's almost definitely the resistor block. Remove it from the duct it is sitting in and look at it. If any of the coils of wire is melted or missing bits, there's your culprit. If your year is hard to find, you could probably rig another year to work, or use some surplus high-watt resistors.

Olds64

This resistor block is generally on the firewall side of the air plenum. It is fastened to the air plenum with two screws and has a wire connector on the backside.

svnt442

To me knowledge when the resistor block takes a dump the fan won't work unless the switch in in the high position. I don't know what would cause it to be high all the time.

MDchanic

I don't think he said High, just that it's on.

svnt442

OK again if the resistor blows the circuit is dead and the fan shouldn't come on at all. High bypasses the resistor all together so that's why it will work on high if the resistor dies.
So the fan being the same speed on all settings is a bit confusing.

MDchanic

I agree.
I don't know the pre-'68's - does the '66 also have the relay, or does it only have the resistor block?

I'd expect at least one dead speed if the resistor were blown, but that's why I said to actually look at it - I can't think of anywhere else that could have any chance of causing this.

Coltonis

I would start with the fan switch. For one, it should be relatively easy to remove and two it will be a much more definitive test. If it checks out then work your way back to the fan motor.

I'm not familiar with your year specifically either, but the predominant arrangement is a live wire (12V) comes into the fan switch then the switch connects the power to a different branch (wire) for however many speed settings there are. (ie if there are two speeds there are usually three wires on the switch.) The two wires will be connected to each of the resistor wire coils that are mounted in the blower box. (Could be one to a coil and one straight to the fan motor, too, but I think mine has two coils so I'll go with that.) The resistor coils control the amount of power going to the positve lead of the fan motor and then the motor ground wire is connected to the firewall to complete the circuit.

Depending on how it is designed the coils could be used independently (ie when one coil is connected the other one is disconnected) or in combination (ie for one speed power is applied to a single resistor coil and for the other it is applied to both coils).

Testing the fan switch should allow you to deduce for sure what the design is. All you need is a multi-meter with a continuity mode. Check that for each switch position there is a unique electrical continuity at the terminals. So, if none of the terminals have continuity between them in the off position at least two of the terminals should have continuity in the low position and then depending on the circuit design I mentioned above the next setting should have continuity between either a different terminal or all three.

You could be testing things for a long time if you don't start at the switch. No point in fiddling with anything else if the switch isn't doing its thing properly.

Err...I think. lol


PS. After the switch checks out i would check that the speed wires are still electrically "seperate" on both ends of the harness. The fan blower in particular juices a lot of current which will cause the wires to heat up. If they get too hot the sheilding melts and the conductors can short out inside the hareness at some random place (that is usually a PITA to get to). This would cause only one speed to be available to the fan also.

compedgemarine

I think my first question would be has there been any electrical work done? I have run across several cars where the PO tried to fix/change something and put wires in the wrong place. it can cause all kinds of interesting issues.

Thomas Simcich

Checked the fan again and now it never comes on. No fan speed at any selection. Guys, can't it be something simple like a blown fuse? Why does everything have to be so complicated? Many thanks to everyone for your help.

MDchanic

NOW it can be.

But a blown fuse won't make every setting blow at the same speed, unless that speed is Zero.