Heater question...
Junior User
Joined: Jan 2001
Posts: 65
Likes: 0
From: Alaska
Heater question...
My heater only works on high. Its a 71 F250. I have swaped in a swich from another parts truck so i don't think that is the problem. Anyone have any ideas what might be causing the low and medium speeds to not work? How is this thing wired up?
Thanks, Craig
Thanks, Craig
Thread Starter
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New User
Joined: Jan 2008
Posts: 0
Likes: 24
Heater question...
There should be a resistor in the heater plenum.
Just un-screw the two mounting screws and check to see if the resistor is shot.
Dennis
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Just un-screw the two mounting screws and check to see if the resistor is shot.
Dennis
F.T.E. Assistant Administrator
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Elder User
Joined: Mar 2002
Posts: 609
Likes: 0
From: Watauga TEXAS
Heater question...
He means the heater box- Look for two wires that look like they hook up to the duct work on the passenger side (I think). Pull the two screws that hold it in place and pull it out. Two of the springs (resistors) are probably broken.
Joe
Joe
Laughing Gas
Joined: Oct 1999
Posts: 1,165
Likes: 3
From: central Alberta
Heater question...
There's an orange and a black wire going toward the front side of the heater housing. You will have to tilt the housing back to access the resistor. There are two coils of wire on it of different resistance. These allow current through at different rates to give you your fan speeds. That's for the two lower speeds and high speed is straight twelve volts. A dead resistor will give you only the high speed.
mike
mike
Elder User
Joined: Jun 2002
Posts: 851
Likes: 0
From: Elizabeth City, NC
Heater question...
Correct me if I'm wrong, an open resistor would yield no current flow. Therefore with a slower speed selected the fan would not turn at all. Resistor hardly ever short, for more than a millisecond anyway, which would have to be the problem to see full current at the motor if these resistor are in series. I would have to see a schematic to believe that this problem is caused by an open resistor.
Russell
1968 F250 LWB 300-6
FORD=First on Race Day
#88 Dale Jarrett-9th in 2002
#21 Elliott Sadler
#97 Kurt Busch-3rd in 2002
#28 Ricky Rudd-10th in 2002
Russell
1968 F250 LWB 300-6
FORD=First on Race Day
#88 Dale Jarrett-9th in 2002
#21 Elliott Sadler
#97 Kurt Busch-3rd in 2002
#28 Ricky Rudd-10th in 2002
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Elder User
Joined: Mar 2002
Posts: 609
Likes: 0
From: Watauga TEXAS
Heater question...
Russell-
This happens all the time. It was also very common with the GM cars and trucks that used the same design. One or two of the resistors would burn in two and the corresponding speed would be lost. The other speed would not be affected and would still be functional.
Joe
This happens all the time. It was also very common with the GM cars and trucks that used the same design. One or two of the resistors would burn in two and the corresponding speed would be lost. The other speed would not be affected and would still be functional.
Joe
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Laughing Gas
Joined: Oct 1999
Posts: 1,165
Likes: 3
From: central Alberta
Heater question...
Russ, I should clarify what I meant. When I said a dead resistor will give you only the high speed, I was referring to the fact that the wire for the high speed position bypasses the resistor assembly totally, supplying a full twelve volts to the blower motor.
mike
mike
Elder User
Joined: Jun 2002
Posts: 851
Likes: 0
From: Elizabeth City, NC
Heater question...
Ok I see now. So the heater fan will only operate when the selector switch is on high. I misuderstood you, I thought you meant that no matter what speed you had selected on the switch it would always run on high.
Russell
1968 F250 LWB 300-6
FORD=First on Race Day
#88 Dale Jarrett-9th in 2002
#21 Elliott Sadler
#97 Kurt Busch-3rd in 2002
#28 Ricky Rudd-10th in 2002
Russell
1968 F250 LWB 300-6
FORD=First on Race Day
#88 Dale Jarrett-9th in 2002
#21 Elliott Sadler
#97 Kurt Busch-3rd in 2002
#28 Ricky Rudd-10th in 2002
Junior User
Joined: Jan 2001
Posts: 65
Likes: 0
From: Alaska
Heater question...
[updated:LAST EDITED ON 19-Dec-02 AT 12:09 PM (EST)]Can anyone tell me where this resister is located? Can I get to it with out removing the heater box? Where is the heater plennum?
Thanks again...
Thanks again...