73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: LiamC20Chev on November 01, 2017, 09:14:30 am
-
I have a 77’ C20 and Every time I turn on the accessories just before I actually turn it over the fan on the passenger footwell side starts running immediately. Even with all the fan/heat/AC switches turned off, it runs immediately when the accessories are on.
Is this normal?
Sorry if it’s a newb question but this is the first Chev I’ve owned.
Sent from my iPhone using Tapatalk
-
That is totally normal for the vehicle. Its purpose is to maintain air circulation through the ducts and cabin to prevent mildew formation in the ducts and provide a constant turnover of cabin air.
-
That's correct, GM designed it to always run the fan on low. There is no "off" position. Also, if you have an A/C truck, and put the A/C on the max position, it should turn the blower on high. It also closes off two of the vacuum-operated doors so that you get recirculated air.
Another item to check is the fuse for high speed, and the blower relay. The blower relay is mounted under the hood on the A/C plenum (passenger side), and on high speed this relay puts the full 12 volts to the fan, and bypasses the resistors used for lower speeds. I'm not sure if a non-A/C truck has the same relay.
Running across the top edge of the firewall there is a power wire (orange, I think) for the blower relay, with an inline 30 amp fuse in a bullet-shaped fuse holder. For some reason this fuse holder often runs hot, and you may find that the fuse holder is melted, which will usually knock out high speed on the blower motor. You can replace it with a newer blade fuse holder and 30 amp fuse.
Bruce