Blower motor power draw?
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Senior User
Joined: Jun 1999
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Blower motor power draw?
Greetings,
Here's the problem: Whenever I run the A/C on my 1988 F150 351W at full, the voltage drops to 12VDC or less while at idle. (it will go to about 12.5 or 13 when at 1000RPM or more.) When this happens my turn signals blink about once every two seconds or so. I have replaced the alternator, regulator, battery and blower moter. If I connect the blower motor directly to the battery it only draws 15-20Amps and does not suck the voltage down any. So Im guessing that there is a problem with the power going to the blower through regualar means? Am I making any sense?
I guess what Im trying to say is that the voltage drops at least two volts with the blower on full.
I greatly appreciate any ideas/suggestions!
Thanks much!
Here's the problem: Whenever I run the A/C on my 1988 F150 351W at full, the voltage drops to 12VDC or less while at idle. (it will go to about 12.5 or 13 when at 1000RPM or more.) When this happens my turn signals blink about once every two seconds or so. I have replaced the alternator, regulator, battery and blower moter. If I connect the blower motor directly to the battery it only draws 15-20Amps and does not suck the voltage down any. So Im guessing that there is a problem with the power going to the blower through regualar means? Am I making any sense?
I guess what Im trying to say is that the voltage drops at least two volts with the blower on full.
I greatly appreciate any ideas/suggestions!
Thanks much!
Postmaster
Joined: Jul 1999
Posts: 3,172
Likes: 4
Blower motor power draw?
Is the blower motor making any noises like its bearings are on the way out ? How big is your battery ? On any other setting but high , the fan's current goes thru a resistor , this is how the various fan speeds are achieved . On high the current bypasses the resistor . Are you running any other high draw electrical parts ? Check all the underhood grounds & the battery's ground cable & make sure they are all clean & secure .
Elder User
Joined: Apr 2001
Posts: 772
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From: Glen Burnie Maryland
Blower motor power draw?
Blower on high with voltage drop is normal.
The problem is that Ford, and all the other Auto makers power the blower motor from the fuse panel(from the alternator) and not from the battery (directly via a separate relay). The supply wires to the fuse panel are never of a sufficient size to handle all the loads at once or a heavy load without the rest of the system showing a drop.
What your seeing is a voltage drop from the alternator feed to the system. The alternator is NOT designed to make a lot of volts/amps at idle speed. That's why you have to rev the engine to raise volts/amps. It won't hurt anything and all the accessories are designed with a operating voltage range from approx. 10V-15V.
If your really worried about this, wire up the power to the battery thru a HEAVY DUTY relay that is switched off the ignition, this will keep you from leaving it on when you shut off engine and killing the battery.
Larry
The problem is that Ford, and all the other Auto makers power the blower motor from the fuse panel(from the alternator) and not from the battery (directly via a separate relay). The supply wires to the fuse panel are never of a sufficient size to handle all the loads at once or a heavy load without the rest of the system showing a drop.
What your seeing is a voltage drop from the alternator feed to the system. The alternator is NOT designed to make a lot of volts/amps at idle speed. That's why you have to rev the engine to raise volts/amps. It won't hurt anything and all the accessories are designed with a operating voltage range from approx. 10V-15V.
If your really worried about this, wire up the power to the battery thru a HEAVY DUTY relay that is switched off the ignition, this will keep you from leaving it on when you shut off engine and killing the battery.
Larry
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