Heater upgrade.

[HO455]

Since fall seems to be right around the corner I will post the blower fan upgrade I did on my Burban here for everyone who shuns the Suburban section. I did this back in March of 2022 and has worked flawlessly since.

For the most part I am cutting and pasting the information from my Working Man's Burbon thread.

The heater blower on the WMB was starting to die. Some times on start up or shut down it would give out a mournful wail. It also seemed low on air output. So me being me I was unable to simply just replace it, I am going to put an A/C blower motor instead of the heater only blower. Because modified is better right?

The A/C blower turns at a higher RPM and moves more air but draws more amperage than the heater only one. GM added a high speed relay circuit to safely supply the higher amperage on a vehicle with A/C.

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 amp 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. (Although since then I have found that running in medium speed is my new favorite speed.)

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. The first photo shows my CAD plan for the new wire to the blower from the relay. (CAD= cardboard aided dimensioning)

I will be using a Bosch style lighting relay instead of the factory style relay. (Last photo.) Mostly as I already have 5 of them being used on the truck already. Consistency is good in my world.

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