[HO455]

The heater blower is starting to die. Some times on start up or shut down it gives out a mournful wail. Not to mention it seems to be low on air output. So being unable to simply just replace it, I am going to put an A/C blower motor instead of the heater only blower.

The A/C blower turns at a higher RPM and as such draws more amperage than the heater only one. GM added a high speed relay circuit to adequately supply the higher amperage. For my conversion I made a hybrid wiring harness that will plug into my existing blower switch and the low/medium speed resistor. Then the relay will supply power to the blower when the switch is in the high speed position. The relay will supply power through a 20 amp fused separate line the way the factory did.

The low/medium speed will be supplied by the existing 10 fuse and wiring. My interweb research was unable to determine if there is a difference in the resistor values of a heater only resistor block and a A/C resistor block. They are physically different but electrically I don't know. The same goes for the blower speed switch. But leaving them on the original fuse size should protect them. It may not be an issue as I generally have the blower on full or off.

I upsized the blower supply wire to 12AWG to match the factory A/C wiring (See link). Fortunately I was able to remove the firewall grommet from the old harness I used to make the conversion harness and after lubing it and the wire up I got the larger wire through it. I wanted to keep the rubber booted connector at the blower so I cut the old 14AWG one as close as possible and soldered it to the larger wire. The rest was just swapping the wires around and crimping some new Packard connectors on.

I will be using a Bosch style lighting relay instead of the factory style relay. Mostly as I already have 5 of them being used on the truck already.

More to follow.

https://67-72chevytrucks.com/vboard/...d.php?t=731399