Heater Fan only blows Low

[Caprice Master]

On my 85 Caprice, the fan switch only works on Low, and no matter
which setting it is on, it blows on Low. Low, Med, High all blow as if it is on Low. The blower motor is 4 years old, so I think it is OK. Is it time to replace the switch ? Could it be the blower, or something else?
Thanks

[TommySS]

Before spending any more money, check all the connections to the blower motor, the relays, and the switch.

Inspect for corrosion, arcing, burned wires, shorted contacts, loss of ground. This is a cheap, albeit somewhat labor intensive chore that you're gonna end up doing anyway, so start with that. Sand the connectors and put some dielectric grease on them before reassembly.

Before replacing the switch, cycle the switch rapidly (i.e., low-high-low-high-low-high, etc) to see if that cleans the contacts.

If that doesn't work, check the blower motor relay. The default is "low" speed and faults usually result in loss of "high".

If that doesn't work, then pull the switch and look for burned contacts/replace if necessary.

If the car has sat for any particular length of time, the relay/switch contacts may have corroded.

Good luck

[Caprice Master]

------------
Before replacing the switch, cycle the switch rapidly (i.e., low-high-low-high-low-high, etc) to see if that cleans the contacts.
-------------

Tommy S.S.

Thanks. I did that and now I have High back. So I have Low and
High, which should be fine. If and when High goes away, I guess I'll replace the switch or bypass it somehow.

[TommySS]

The contacts must've been dirty. You can get some contact cleaner from Radio Shack. Spray it on the contacts and then cycle the switch quickly (up/down real fast), and see if medium comes back.

Loss of medium indicates a blower resistor may be blown, which blew because the blower motor is dirty and taking too much juice to turn.