Trucker2k16
Well-Known Member
Hey guys im lost and need a little help my heater fuse keeps blowing i cant find out why i checked blower wires and ac/heater controls.
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Heater fuse keeps blowing
- Thread starter Trucker2k16
- Start date
ak diesel driver
6.5 driver
sometimes as the blower motor ages it will draw more power but still seem to work fine. If you have access to a clamp on ammeter you might see what it's drawing
Trucker2k16
Well-Known Member
I got a oms meter that does amps it never blew with ac but with heat it does
Will L.
Well-Known Member
Ooh, a mystery! Get the Scooby snacks...
Been way too long since messing with the hvac circuitry for my memory. Schematics would be useful here. I cant remember if one fuse covers the blower separate from the control circuits. What is the amp rating on your meter - is in inline or clamp on style? and what size fuse is blowing?
Without schematics and testing each component in it, an optional diagnostic is as follows:
If the blower motor doesn’t trip fuse in a/c, it means thats ok. So control circuit to the system is the cause. Does it blow the instant you turn it to heat?
Does it blow the fuse only when certain commands are given like blower speed; blend levels: vent vs floor or max heat vs 75% heat 25% cool air?
Knowing what ONE change blows the fuse is needed. If you dont know-
With a cold truck, Note the time before beginning. Start truck, Turn on the a/c and operate controls one at a time until you determine what blows the fuse. Leave the fan speed at max setting until all other controls are operated. When the fuse blows note the time.
Now recreate the blown fuse again as fast as possible by doing that one same action that caused it to verify it was the reason. You may need to let the truck cool and restart noting the time incase it is a collective heat/ load causing the over current.
Once the component thread is known, you can test the end device, the control, etc. to verify what is bad.
Been way too long since messing with the hvac circuitry for my memory. Schematics would be useful here. I cant remember if one fuse covers the blower separate from the control circuits. What is the amp rating on your meter - is in inline or clamp on style? and what size fuse is blowing?
Without schematics and testing each component in it, an optional diagnostic is as follows:
If the blower motor doesn’t trip fuse in a/c, it means thats ok. So control circuit to the system is the cause. Does it blow the instant you turn it to heat?
Does it blow the fuse only when certain commands are given like blower speed; blend levels: vent vs floor or max heat vs 75% heat 25% cool air?
Knowing what ONE change blows the fuse is needed. If you dont know-
With a cold truck, Note the time before beginning. Start truck, Turn on the a/c and operate controls one at a time until you determine what blows the fuse. Leave the fan speed at max setting until all other controls are operated. When the fuse blows note the time.
Now recreate the blown fuse again as fast as possible by doing that one same action that caused it to verify it was the reason. You may need to let the truck cool and restart noting the time incase it is a collective heat/ load causing the over current.
Once the component thread is known, you can test the end device, the control, etc. to verify what is bad.
Trucker2k16
Well-Known Member
My ohms meter has probe style. It blew a few seconds after i cut fan on at a stop light if im in the yard just idling and slowly turn fan to hi it seems to not blow its crazy i dont get it. But also i still have heat coming thru the vents after the fuse blew once i got going i could feel heat unless i wasnt moving.
Will L.
Well-Known Member
Sounds like ak diesel driver hit the nail on the head.
You could have bad connections, bad resistor, bad motor, or combination of the 3. Getting into them is your next step. My guess would be Suspect the resistor first and motor second. If you can afford it- plan in both, but install the resistor and test it, then do the motor. The motor getting old puts a lot more load on the resistor causing them to burn out quicker. If tight on money, check the bearings on the motor- could be they get replaced and help for less nickels.
This is to explain what’s happening so you don’t go crazy trying to understand:
Rule of thumb is turning on an electric motor takes up to seven times more amperage to start than to operate. these next numbers are to give the idea- they ARE NOT accurate numbers for your truck. If low operates at 1 amp, it takes 7 amps to get it spinning, medium is 3 amps, it takes 19 amps to get it spinning- notice not 21. Because there is a more load at the first bump that eases as the rate of acceleration increases. In high normally 5 amps taking 33 amps to get it turning.
When you start it on low, 7 amps falls to 1, then you go to medium which goes up to 15 then settles at 3. But the increase is not as high - note 15 instead of the 19 because it was already spinning. Then you bump it to high and it peaks to 23 amps, settling down to 5. Again a peak, but no where near as much load because it was already turning.
Another way to think of it is like driving and mashing the throttle full to get to 60 mph fast as possible. Burns a lot of fuel. As opposed to slowly up to 20, then to 40, then to 60. Slower to get up to speed but less peak load on the engine.
You could have bad connections, bad resistor, bad motor, or combination of the 3. Getting into them is your next step. My guess would be Suspect the resistor first and motor second. If you can afford it- plan in both, but install the resistor and test it, then do the motor. The motor getting old puts a lot more load on the resistor causing them to burn out quicker. If tight on money, check the bearings on the motor- could be they get replaced and help for less nickels.
This is to explain what’s happening so you don’t go crazy trying to understand:
Rule of thumb is turning on an electric motor takes up to seven times more amperage to start than to operate. these next numbers are to give the idea- they ARE NOT accurate numbers for your truck. If low operates at 1 amp, it takes 7 amps to get it spinning, medium is 3 amps, it takes 19 amps to get it spinning- notice not 21. Because there is a more load at the first bump that eases as the rate of acceleration increases. In high normally 5 amps taking 33 amps to get it turning.
When you start it on low, 7 amps falls to 1, then you go to medium which goes up to 15 then settles at 3. But the increase is not as high - note 15 instead of the 19 because it was already spinning. Then you bump it to high and it peaks to 23 amps, settling down to 5. Again a peak, but no where near as much load because it was already turning.
Another way to think of it is like driving and mashing the throttle full to get to 60 mph fast as possible. Burns a lot of fuel. As opposed to slowly up to 20, then to 40, then to 60. Slower to get up to speed but less peak load on the engine.
Trucker2k16
Well-Known Member
I did find out that if i go to hi then back to low it stays on hi unless i play with switch then i hear the heater relay click. I picked up a new relay and a resistor also with new AC controls and a blower motor I'm just trying to find the tube that goes from the Hvac box to the blower motor to keep it cool