Have a 1991 F-250 300ci. and everytime the heater is turned on the battery discharges.I have replaced the battery,alternator,blower motor,wiring harness has been checked and fuse box has been removed and checked.When the blower motor is not used everything is fine.
Battery voltage with engine running and blower motor on,about 10volts,with engine running and blower motor off,about 14volts.
Any ideas? Thanks tjh

 

[updated:LAST EDITED ON 28-Dec-02 AT 01:47 PM (EST)] It sounds like the alternator cant handle the blower motors electrical demand.
Are these voltage readings at idle? If so what RPM is your idle? Does the voltage drop when the engine is running at say 1500rpm and you turn on the blower?
Is the correct sized pulley on the alternator? If it is the wrong size the alt speed is too slow at engine idle speed, and as a result the alterantor doesnt have enough output to maintain high electrical demands.

Sparky

ps
When did this problem start? All of a sudden or after some work was done? Or is this a problem you inherited when you got the truck?

 

Could be the dash ground is loose, but any competent auto electrician should be able to narrow this problem down - that circuit just isn't very complicated. If it happens at all blower settings, then it's NOT the resistor pack. If the motor doesn't get BLAZING hot, it's not the motor. If NOTHING gets unusually hot, then it's either the alternator or the alternator's regulator circuit.

How long does it take with the blower on for the voltage to drop, and how long before the battery is too weak to crank the engine?

 

How about the blower motor is getting so old it is straining to turn which causes it to draw more power?

Perhaps a cleaning & lubing of the motor is in order.




Dennis

F.T.E. Assistant Administrator

http://www.clubfte.com/users/mil1ion/SigSanta.JPG
[font color=red]
"May The Spirit Of Christmas Be An Inspiration To You Throughout The Year"[/font]

[link:www.ford-trucks.com/guidelines.html|Club FTE]

[link: motorhaven.autoanything.com|How YOU Can Support This Site]

[link:www.clubfte.com/users/mil1ion/Mil1ion.html|My Website,"North Of The 49th"]

 

To answer Sparky,big6 and Dennis..the problem with the heater started when the first alternator was changed.The pulley size is correct.the voltage reading are at a high idle.
New blower motor has been installed.
Also if the truck has been running for three hours or so with the heater running and the truck is turned off,then it will not re-start.Also what would be the difference between a factory alternator and a rebuild? Could that be some of my problem?

I might add there has been 3 alternators on that truck.Thanks tjh

The spelling of alternator has been corrected by administration for better efficiency in word related Fte searching

 

[updated:LAST EDITED ON 28-Dec-02 AT 06:33 PM (EST)]If it worked before the alt change, and NOT after, I'd have the alt tested at several places - many parts stores do it free on the vehicle or off. I'm still leaning toward an alt/VR problem.

It's not painted, is it?

 

The Big Four Huge Gobblers of Electric power in a Automotive application.

Not in any specific order:
1)Headlights
2)Heater Motors
3)Air Conditioners
4)Windshield Wipers


Dennis

F.T.E. Assistant Administrator

http://www.clubfte.com/users/mil1ion/SigSanta.JPG
[font color=red]
"May The Spirit Of Christmas Be An Inspiration To You Throughout The Year"[/font]

[link:www.ford-trucks.com/guidelines.html|Club FTE]

[link: motorhaven.autoanything.com|How YOU Can Support This Site]

[link:www.clubfte.com/users/mil1ion/Mil1ion.html|My Website,"North Of The 49th"]

 

You forgot the starter!

 

Thank Steve, I should have said with the engine sometimes Running or Not.

The starting sytem is different.

But you knew that!

Dennis

F.T.E. Assistant Administrator

http://www.clubfte.com/users/mil1ion/SigSanta.JPG
[font color=red]
"May The Spirit Of Christmas Be An Inspiration To You Throughout The Year"[/font]

[link:www.ford-trucks.com/guidelines.html|Club FTE]

[link: motorhaven.autoanything.com|How YOU Can Support This Site]

[link:www.clubfte.com/users/mil1ion/Mil1ion.html|My Website,"North Of The 49th"]

 

[updated:LAST EDITED ON 29-Dec-02 AT 03:27 AM (EST)]>..the problem with the
>heater started when the first alternator was
>changed.The pulley size is correct.the voltage reading are
>at a high idle.
>New blower motor has been installed.
>Also if the truck has been running for three hours or so
>with the heater running and the truck is turned off,then it
>will not re-start.

I think I have to vote for a voltage regulator problem. Does it have an internal one? Also if you have tried several different alternators with the same result you could be having a wiring problem Like corrosion....electricity's biggest foe
Check and clean the wiring connectors on the alternator/regulator.

Sparky

 

i think it sounds somewhat like a bad ground somewhere causing the alts to short out or the vr is shot. when you turn on your blower does it slow the engine down like its straing? and also it may not be a bad idea to cheack your wires from the alt to the bat. oh and you forgot the amp as being a big puller pwr wise. myne almost made the headlamps go completly off and my cousins would kill the truck.