Heater/ac blower
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Junior User
Joined: Feb 2003
Posts: 55
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From: Alabama
Heater/ac blower
Hi;When I turn on the heat or ac in my 89 f150,the volt meter immediately goes to discharge.When I turn it off the meter goes back to where it was.Do you think I have a bad fan motor or should I be looking at something else like those resistors,which makes the fan go from the low speed to the high speed?Also,if it is the fan motor,how hard is it to replace the motor?
Thanks for the info;
Jack
Thanks for the info;
Jack
Elder User
Joined: Sep 2004
Posts: 941
Likes: 4
If the blower spins at the appropriate speed at the various switch settings, there is probably nothing wrong with it.
It is normal for the vehicle voltage to drop somewhat when you turn the blower on, especially at idle, and especially if you have the headlights on as well. You can reduce this somewhat by cleaning up the battery connections and chassis grounds. If the alternator has a bad diode, the voltage drop will be larger and persist to a higher RPM.
The voltage should not drop with the vehicle at 1500 RPM or more with good battery connections and clean grounds. If it does, the blower motor may be bad. It is not hard to change it out.
Remember that the alternator current output is a function of engine RPM, and that it is common for vehicle alternators to not be able to keep up with the worst-case load when the engine is idling.
For all that we make fun of Ford's "idiot light" oil pressure guage, sometimes guages provide "too much information" -- as may be happening here.
It is normal for the vehicle voltage to drop somewhat when you turn the blower on, especially at idle, and especially if you have the headlights on as well. You can reduce this somewhat by cleaning up the battery connections and chassis grounds. If the alternator has a bad diode, the voltage drop will be larger and persist to a higher RPM.
The voltage should not drop with the vehicle at 1500 RPM or more with good battery connections and clean grounds. If it does, the blower motor may be bad. It is not hard to change it out.
Remember that the alternator current output is a function of engine RPM, and that it is common for vehicle alternators to not be able to keep up with the worst-case load when the engine is idling.
For all that we make fun of Ford's "idiot light" oil pressure guage, sometimes guages provide "too much information" -- as may be happening here.
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