No speed control on heater blower motor

1998 FORD E-SERIES VAN
92,420 MILES • 6 CYL • 2WD • AUTOMATIC
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WATFORD
  • MEMBER
  • 2 POSTS
This is my second winter with no real heat.
I discovered by turning function control to vent with maximum heat on dial I get a little heat drifting into the cab, but this is really not adequate enough especially when demisting is required on the windshield.
What I have done so far is check fuses, replaced blower motor, checked resister and replaced but think the old one is still good.Also have bought a new 4 wire pigtail and fitted. But found this to be burnt and socket has crumbled so needs replacing again.
I read your remedy on this and tried to find power with multi-meter with ignition on.
All 3 colored wires had 6 volts and the thick black ground wire had no power.
Any suggestions please?
Nov 18, 2019 at 5:21 AM
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JACOBANDNICKOLAS
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  • 110,175 POSTS
Hi.

You should see different voltages at the resistor. I attached a pic and will explain how this works. First, power isn't supplied via the switch but instead, the switch is a gateway to ground. If you have the switch on high, 12v should be supplied to the blower motor. As you slow the speed down, power flow changes to different locations in the resister which causes voltages will lessen.

The idea that the connector was brittle and needs replaced again indicates there is a bad connection at some point allowing the power to most likely arc in the connection and create excessive heat, or the blower motor is drawing too much amperage. With that, you checked power at the resister. Was there 6v at all of the connections all the time? If that is the case, replace the blower motor switch. It is shorted internally causing excessive power to the resister and heating up the connector..

If that isn't the case, I suspect one of the grounds is weak or missing. Take a look through the schematic I provided. Make sure there is 12v to the motor itself (orange/red wire). If there is, check the two grounds I circled. One is for the switch and the other the resister.

Do this and let me know what you find. Remember, when checking ground, there will be no power. You are checking for continuity between the connector and a known good ground. Your multi meter should be set for testing ohms.

Here are a few links you may find helpful:

https://www.2carpros.com/articles/how-to-use-a-test-light-circuit-tester

https://www.2carpros.com/articles/how-to-use-a-voltmeter

https://www.2carpros.com/articles/how-to-check-wiring

Let me know if this helps, what you find, and if you have other questions.

Take care,
Joe
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Nov 18, 2019 at 7:15 PM
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WATFORD
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Hi Joe,
Thank you for answering my question so concisely.
I took the dashboard cover off and removed the blower switch along with the 4 wire connection, both were burnt.
The socket was melted and falling apart.
After replacing the switch and splicing new wiring onto the old harness to the blower I now have a properly functioning heater.
Prior to to permanently splicing these wires I checked very well they corresponded to the correct low to high settings.
Thank you Joe for your excellent help!
Nov 25, 2019 at 8:31 AM
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