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

[HO455]

I did the same kind of A/C blower motor upgrade in my GTO years ago and several years later the fan switch started acting up and after disassembly I discovered the contacts were arced and burnt. Fortunately I was able to rebuild them with some solder. It could have been the switch was just worn out from over 200k miles or the A/C blower was too much or some combination of both.

Whatever the cause was I haven't had to mess with it since. Its not a daily driver anymore but has over just 300K on it now. It's likely to last forever now since I picked up a spare switch years ago.

Here is a schematic of the hybrid harness I built.

[HO455]

And the results are in! The A/C blower is a significant increase in air movement. Especially over my old one.

Before the blower was replaced we used my buddy's hand held anemometer to measure the output on the passenger side defroster vent.
The old motor air output registered 7.2 mph.
The new blower motor motor with the unmodified (Factory) harness registered 9.4 mph. (The photo only shows 9.1 due to me being unable to hold the anemometer and take the photo at the same time.)
And the new blower with the hybrid harness registered 12.7 mph!
The anemometer confirmed what my ears had told me.

During the testing the 10 amp fuse in the fuse box blew so I replaced it with a 15 amp that seems to be holding. I have yet to get a amperage measurement but as soon as I get a new a battery for my multimeter. I decided that the fuse blew due to the increased amp draw on start up once running at speed the amperage dropped below 10 amps.

In order to mount the relay on the really convenient tab on the heater box (Photo #2 green arrow) I had to lengthen the wire from the high speed contact on the blower switch to the relay coil.

The hybrid harness was made using parts of a factory non-A/C harness.

[truckster]

I have factory A/C, but I wanted more air flow. I used this thread as a starting point:

http://www.67-72chevytrucks.com/vboa...ghlight=blower

I did it a little differently. I cut the back off my blower wheel and used JB Weld to secure it to the new one. It blows air like a modern vehicle does.