Dash HVAC fan speed only operates on slow.

August 20, 2024, 12:59:32 pm

I have replaced the OEM 3-speed switch with a new one from FOT parts. This has not resolved the issue. I have contacted FOT technical support via email and requested a schematic of the dash HVAC wiring system and any suggestion they would have to resolve the issue. I mentioned that it was difficult for me to travel the 750 miles to FOT. After only 5 days they did respond thusly:

Service normally sees the rectifier bridge bad.
Foretravel does not write service manuals for installed equipment.
Recommend scheduling a service appointment with FOT for repair.

A search of the Foreforum brought up this thread:
No High Speed Fan on Dash Vent

I have attempted to contact Forum members but still do not know how to proceed. The schematic in the thread shows a device (relay? or bridge rectifier?) with two yellow wires going to it. That is my best guess as to what part may have failed. But I cannot locate where the device is located in my dash. I have attached a picture of my dash. Five relays marked 1-5 are labeled 4RD 960388-08 by Hella. I associate Hella with fog lights and headlights. Are the bridge rectifiers to the right of the Hella relays? Could someone help identify what device I need to replace and where it is located on the attached photo?

Thanks

Bob

Re: Dash HVAC fan speed only operates on slow.

Reply #1 – August 20, 2024, 06:04:31 pm

In your picture, there are 5 relays marked 1-2-3-4-5. To the right of them are 6 bridge rectifiers.

In my case, the fan worked on low and medium but not high. After chasing wires in the dash, I found the red wire from the switch did not have continuity to the connector at the other end (also in the dash). I ran a new wire and have had no issues since.

See the right side of this schematic.

This is for my 2003.

Re: Dash HVAC fan speed only operates on slow.

Reply #2 – August 20, 2024, 07:10:03 pm

Do you have a multi meter so you can check the voltage at the blower switch?

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