Dash AC/Heat Blower Acting Strangely

[jfxg48]

About 5 days ago I noticed a problem that I have not yet had time to jump on.

The dashboard mounted AC/heat console on my '02 DutchStar is pretty standard, I presume; four-speed fan selector, variable temp selector, and multiple modes of heat, a/c, or vent. (I tried to include a pic but the forum wouldn't take it)

The problem is that when I select any operating mode other than "vent", the blower motor cycles on and off rythmically. The cycling rate depends on the fan speed selected; slow blower will cycle at about 8 seconds on, 8 seconds off, while high speed blower cycles at 3 seconds on, 3 seconds off. As far as I can tell, the unit still seems to produce warm or cold air respectively, only the fan speed cycles. In the vent mode, the blower fan runs continuously at the selected speed, and the temperature is variable.

Has anyone encountered this sort of thing before? The cycling is so precise I'm thinking it is some kind of preset behavior to highlight a failure somewhere in the system.

As always, thanks in advance.

John

[dickandlois]

John,

Sounds like a current or thermal issue. I'm going with the current thought, in the supply voltage circuit, not a thermal breaker in the motor housing.

You could just disconnect the blower motor plug and supply 12 volts and a ground directly to the motor. If it works fine, a circuit issue. If it turns on and off its a blower motor issue. There is a resistor array built into the blower circuit for the speed(s) one bad connection at the common circuit point could also cause issues.

There might be a auto reset breaker in the 12 volt supply that is just weak. A weak one would auto reset faster as the higher current required for the faster motor speed increases.

Could be a thermal reset in the motor that is cycling the same way. Not a common setup though. That would require replacing the blower motor.

I would look for the fuse, should be in the 12 volt dc supplied from the main power buss, through a fuse to the motor in a circuit controlled by a power relay. The switches built into the dash control do not have high current capability. If you find a reset type fuse, jumper it and see if the problem goes away.

Rich.