Max AC control fan.

[Freedomring]

Just looking for some feedback. When I turn my dash AC control knob to max AC the fan slows down gradually then stops. It's not the switch all power is there, and the switch is new. Any ideas on where the trouble may lie?

[DavidL]

If the fan motor has constant voltage and solid ground, it should spin the same speed.  If it slows down, possibly overheating, brush resistance, bearing seizing (but there should be a noise associated with that).

Did you check the ground?  Possibly, the fan is a variable speed motor, and the ground changes to change the speed?

A voltmeter on the fan motor leads should tell the story.

[Tom Cherry]

40 minutes ago, Freedomring said:

Just looking for some feedback. When I turn my dash AC control knob to max AC the fan slows down gradually then stops. It's not the switch all power is there, and the switch is new. Any ideas on where the trouble may lie?

Try this trouble shooting….  If you can. Put a VOM on the fan motor wehn you switch it on.  If the switch is putting out a constant 12 VDC or whatever, then monitor it.  The voltage should stay high or close to the original.  If the voltage remains high or doesn’t vary, then the motor is seizing up.  If the original switch was OK, then the issue is in the motor.  You can also put a SPDT switch with the center out to the motor.  Hook up one side to the switched 12 VDC.  Then the other to a known good 12 VDC source.  Turn on the system.  Then if the motor starts slowing down, flip the switch.  If it continues to slow down….motor….if it speeds back up….switch or a high resistance connection somewhere.  You can also check, the incoming voltage to the switch before and after turning on the fan.  

Gotta know that you have good voltage…. Lowering the voltage causes a spike in the current draw.  More current draw heats up windings and/or damages the brushes.  Fan may or may not have a resettable thermal overload.  See if you can find the specs on the motor and then do some research on whether it has a thermal overload.  No way to tell you, or at least I can’t, without knowing the characteristics of the incoming power.

[Happycarz]

Another thought; does the motor physically slow dow or is the air that is coming out of the registers (outlets) slowing down.  
 

After checking the motor voltage with the selector in both positions, you will know if it a motor issue or if the plenum doors are not directing airflow to the proper outlets.  
 

If you haven’t yet tried, see what happens with the selector in each of the different positions. 
 

Just trying to cover all bases with your issue.
 

 

[Bill R]

Have you visually looked at your fan to see it has stopped spinning?  You could be freezing up in the evaporator coils thinking it is the fan.  Something to check.