heater fuse blows when truck is running

[dmjlambert]

Well that is interesting. I would say if it is a replacement for non a/c and a/c trucks, that means it is an a/c fan. Perhaps the true heater fan is not available easily. The a/c fan draws more power and is more powerful.

The thing is, if a truck has a/c and runs the more powerful fan, they not only have a bigger fuse, but the wiring includes a relay to power the fan at the highest speed so all the current is not going through the fan selector switch. The "four season system" section of the wiring diagram shows the wiring for that, and I don't know if there is an online version of that diagram, but here's one attached. I don't know if Chevrolet is different from GMC but I'm thinking probably not. This is for 1969 Chevrolet. I'm thinking it may be a good idea to use a relay for the high speed, in addition to increasing the fuse rating.

[coldgin]

Thanks for the diagram

[HO455]

Originally Posted by dmjlambert

Well that is interesting. I would say if it is a replacement for non a/c and a/c trucks, that means it is an a/c fan. Perhaps the true heater fan is not available easily. The a/c fan draws more power and is more powerful.

The thing is, if a truck has a/c and runs the more powerful fan, they not only have a bigger fuse, but the wiring includes a relay to power the fan at the highest speed so all the current is not going through the fan selector switch. The "four season system" section of the wiring diagram shows the wiring for that, and I don't know if there is an online version of that diagram, but here's one attached. I don't know if Chevrolet is different from GMC but I'm thinking probably not. This is for 1969 Chevrolet. I'm thinking it may be a good idea to use a relay for the high speed, in addition to increasing the fuse rating.

Don't forget the resistor and the switches are built to handle the larger amperage of the A/C blower motor. Found that out the hard way on my GTO. Yes, the A/C blower made my defroster work ten times better, but when the switch and wiring melted a month later it wasn't so good. And back then switches were a junk yard only part. So it was a cold couple of weeks.

[coldgin]

Talking to some buddies at work they both have 65 c10....have replaced their blower motors....one of them had same problem and just replaced 10a fuse with a 20a....no more problems....it is a non a.c. truck....still haven't got into the truck yet....hopefully this week

[HO455]

If you can get a DC amp-meter measure the amp load as close to the fuse as possible. If is about 15 amps you should be ok. The higher the amp draw is the more likely you will have issues with the switch down the road.