eljefedavies

93 LE extended cab 4WD. I have looked everywhere and could not find my problem. My blower motor does not work on heater or defrost. It works on every other setting and all the speeds work. When I switch it over to heater or defrost I can a very vague noise coming from the vent/box which is over the transmission tunnel but nothing else. If I have the setting on vent with the heater on the highest setting the blower works on all speeds and I get heat from the vents. I have read that there is a vacuum that works the heater and the defroster. Could a faulty vacuum system cause the blower not to work? Thanks for any help

simplysmn

Or better yet a broken Vac line or jammed up selector valve on heater

thrashingcows

Yup sounds like either one of the vacuum operated doors is not opening, or switching the way it should.

There is a big block of vacuum lines that run up to your heater control panel. Some times one or more of the nipples on teh heater control panel break off. If this happens then the vacuum will not get re-directed to the proper pot.

As simplysmn said you could have a vacuum line worn through as well. Or you might have a bad vacuum pot, or the door in the heater box itself could be seized up at the pivot points.

Jim Lane

All of the operations of the blower motor are controlled by the Heater/ Defroster selector switch the Heater Blower Switch and the Blower Motor Resistor.

Here is a wiring diagram for a 1991-93



There is a vacuum switch that is piggyback with the control that routes the vacuum to the proper servo to operate the Recirculate, Heater/ Defroster, Vent and also control the hot water, the vacuum has no control over the blower motor electrical circuits.



If you blower motor is drawing excessive current worst case scenario.
It can burn the contacts in the switch, the fuse panel, wiring harness and ignition switch.

https://www.dieseltruckresource.com/...d.php?t=158400

Jim

eljefedavies

I may have not explained this very well or I may not be understanding your solutions so here I go again. My blower is working fine on A/C and vent, when i press in the heater or defrost button the blower stops. I have opened up the vent box on the transmission tunnel and the door opens fine. I opened up the back of the glove box and can see the vacuum working moving the rod to open and close the vent's. According to Jim the vacuum has nothing to do with the electrical circuit. Is there a connection between the heater and defrost buttons that tells the blower to run? I would think the blower works or doesn't. Obviously I am wrong so please point me in the right direction. Jim I have read al your posts on relays and how to get more power out of your blower. I think my problem is a little different, is it or not? Thanks

Jim Lane

The Heat /Vent/ Defrost lever operates a switch inside the control that turns the blower on and off according to its position.

Check the connector on the rear of the control for loose or burned terminals and sniff the switch to see if it has burned.

You can use the diagram and a test light or DMM to verify the contacts are good as you move it through its operating range.

They need be able to pass about 30 amps.

Jim

eljefedavies

Thanks Jim,
I got the fan to work on heat and defrost. I did not say I fixed it, I just started looking around at the back of the controller and BAM the blower starts working. I could not smell any burning and did not see any signs of it either. I hope it was just a loose connection since winter is around the corner. I have noticed how weak the blower is on heat/defrost as compared to A/C. I will look into doing your upgrade in the future.