Heater Blower Questions

[Gonzo]

Ok I know I'm missing something here but, exactly how does the heater blower work. I just bought one & I hooked it up but when I pulled the lever up it only spins when the blower touches the engine block. What am I doing wrong? Also where do I install it at & what holds it?

[JP Noonan]

The switch give the blower relay a ground, a grn/wht wire goes from the switch to the relay. However if giving the blown a ground turns it on I guess the relay is working. Check the ground point under the relay board I think this is where the fan is grounded.

The fan is mounted differently depending on the year. My 72 had a special bracket that mounted to the 1.7L motor or blower housing. The 75-76 has a mount welded to the driver side engine shelf. The fan is bolted to the mount on the 72 and hose clamped on the 75-76. The fans themselves are also different. The 72 had 2 outlets, the 75 only had one that went to a splitter. BTW my 74 has the mount welded on but didn't come with a fan so I don't know which fan it came with.

if it only works when it touches the block then its not grounded and/or doesnt have a good ground connection, and it mounts on the fan shroud w/ a mounting piece on the back...if you dont have that then you need to get one, hope this helps.

[Dave at Pelican Parts]

JP's right.

A bit more detailed info: The power and ground wires for the blower go to the relay board. The power wire is connected to the output of the heater blower relay, which is controlled by grounding the switch on the heater lever.

The ground wire trace goes through the relay board to the "main" wiring harness (the T-14 connector on the front side of the board). From there it goes to the ground point under the relay board in the lower-left-front corner of the engine compartment.

Check the ground path. Check the wire that goes from the board to the blower (should have ZERO resistance between the end of the wire and the blower case). Check the continuity of the path through the relay board--look at your Haynes book's diagram for the board, or the one Pelican has on-line here. Check the wire from the T-14 connector to a good known ground. All should show a good clean path, zero resistance or VERY VERY close to it. (A couple of ohms is too much!)

Finally, check the resistances of the various parts of the path. Blower case to T-14 connector, blower connector on relay board to ground, blower case to ground. This will help test the connections.

Infinite resistance means a broken wire or trace. Fix or replace the broken wire or relay board. A relatively-high resistance in one of the connected segments means a dirty contact. Disconnect the suspect contact and use a pen eraser, wire brush, or emery cloth to make it shiny. TV tuner cleaner can help also.

Last, protect the ground point under the relay board with some dielectric grease AFTER the connection is together and clean and tight. You don't want water getting in there to corrode things, since corrosion doesn't conduct very well.

--DD