Four speed HVAC fan

[Kkortman112]

Way back in 1993 a farmer I worked for purchased a new eclb K2500 with a 350 in it. Unfortunately he was never satisfied with the towing capacity of it, even after installing a Hyperchip in it. So the following year he traded it in on a eclb K2500 with a 6.5TD which suited his needs much better. Anyway besides having the newer bullet grill and 3rd brake light integrated into the cargo light I believe the HVAC system had 4 fan speeds instead of the 3 the '93 had. Granted it's been a long time ago lol! I was thinking instead of Low, Med and Hi it would read Low, Low-Med, Med-Hi and then Hi on the HVAC screen. If this is correct is it something I could upgrade my '93 to? Is it just as simple as going to a 4 speed resistor setup or is it that plus a different control head and extra wiring? If it's easily obtainable I thought it would probably be a worthwhile upgrade.

 

[R422b]

I don't know anything about that specifically but I run my ac with the blower as high as I can stand the sound of and adjust the temp so I wouldn't think it would be worthwhile.
I find that if you keep the AC on with plenty of air flow and just raise the temp when you get too cold it keeps the humidity low and is more comfortable than if you just keep it on cold and turn down the fan.

That's my$0.02
Sent from my moto g(7) play using Tapatalk

 

[AK49BWL]

It's not that simple unfortunately. What's interesting is my 93 had a 4 speed system.

There's actually a good chance you don't need to change heads, because the later part numbers could run 3 or 4 speed systems depending on a certain pin being grounded at the module. If you get me the 8 digit part number I might be able to say whether it'll run the 4-speed setup. However, if you only have a three speed resistor and only three relays, you'll need to replace the entire HVAC harness, resistor pack, and add the extra relay the four-speed system uses. The nice thing about that is, you don't need to replace the door motors, and the HVAC harness is an independent harness that you can fairly simply hot-swap between trucks.

 

[Kkortman112]

Thanks Brandon. I have 2 of the control heads so when I get time and the next time I have my dash apart I'll snap pictures of the numbers. So I also would need to find a known 4 speed truck and rob the harness and relays/resistor board then too? Interesting that your '93 had 4 speeds, I wonder if there was a special option for it. This was just something I thought of as I was dozing off to sleep last night so I haven't done any real research on it in the parts book or electrical manual but I will now. Thanks!

 

[AK49BWL]

Mine might have been a late 93 model. I can't remember anymore lol. But yes, you would need to grab the full harness, relays, and resistor plate. The relays you have will work, so keep them around as spares, but the 4-speed system uses an additional relay for the extra speed selection. Pretty much ALL 94 models were 4-speed, so that's a good place to start.

 

[someotherguy]

I'd be sure the hole in the HVAC box is the same between the two styles. Those older blower motor resistors were pretty different; the larger hole and the two screw holes may not be the same pattern, and you'll probably end up dropping the dash to modify that. Not that it's a huge deal on an 88-94, but just an FYI to watch out for.

Richard

 

[Kkortman112]

When I have some more energy and free time I'll do some looking in the parts books and service manual's. I just thought this might be a cool mod if it isn't too hard to do. Was 120° in the old tubing mill today so I don't have much motivation tonight lol!

 

[east302]

High would be the full 12V (or so) to the fan regardless, right? In other words, would an 88 with the three speed blow the same cfm as a 94 if both were on high?

 

[AK49BWL]

Should. The four speed systems only add a speed between what would be med and hi on the 3 speed systems.

 

[Kkortman112]

I personally just thought that it would be nice to have 2 intermediate speeds instead of just one. From what I have found out early 93s still had the 3 speed like my truck which was built in early November 1992 at Ft. Wayne but later 93s had the 4 speed fan controls, it wasn't just a 94 year feature.