Gmt800/900 fan in Gmt400?

[400North]

Hey, so I wanted to upgrade my fan blower motor since it starting squealing, only works on high (I gotta change the resistor still), and the air it pushes out of the vents on high is terribly low (and yes I’ve done just about every other thing mentioned in other threads to “fix” poor airflow).

So my question is, does anyone know the voltage/amps of a gmt400 and a gmt800/900 blower motor? And possibly of the resistors? I don’t know much about electrical and don’t want to burn my Yukon down haha.

I just finished cutting up my hvac box where the blower motor sits to fit a gmt800/900 blower motor and it seems to push more air through the vents (it’s done but not done well haha, the section where the blower motor sits is removable but I cracked and broke some of the plastic since I didn’t know the best way to remove it at the time so a lot of air was coming out behind the dashboard when I tested it, so I will get another one for my final assembly, and will have to find a way to properly secure the blower motor to the hvac box since the blower motor I got just twists into place). Once I am done and happy with my final result I can post another thread on how I did it if people want (and if I find that it makes a considerable improvement, part of me thinks that the path of the air in the hvac box is sort of the low airflow culprit).

 

[98chevy2500SS]

One way to test how much voltage is coming out of the blower motor is using your volt meter with those sowing "T" pins stuck in behind the connector (of course, the truck needs to have the key 2 clicks forward to get the blower running). Once your resistor gets replaced, then you should get a reading of how many volts the blower motor is putting out when you start going through the speeds on the climate control unit.

 

[HotWheelsBurban]

The 800 series blower motor has threads on it like a big jar lid, so it just screws into the HVAC box. If you could find a damaged one in the yard, and graft that part of it to the 400 box, that may help....

 

[400North]

One way to test how much voltage is coming out of the blower motor is using your volt meter with those sowing "T" pins stuck in behind the connector (of course, the truck needs to have the key 2 clicks forward to get the blower running). Once your resistor gets replaced, then you should get a reading of how many volts the blower motor is putting out when you start going through the speeds on the climate control unit.

Okay thanks, ya I will have to replace the blower motor resistor first. Then I can use that to check the voltage difference between the gmt400 and gmt800 blower, thanks!

 

[400North]

The 800 series blower motor has threads on it like a big jar lid, so it just screws into the HVAC box. If you could find a damaged one in the yard, and graft that part of it to the 400 box, that may help....

Ya I was thinking of getting a gmt800 hvac box from a junkyard and plastic welding just the section where the blower motor sits to the gmt400 box. I will see what I can find/make this week.

 

[stutaeng]

If possible, get early GMT 800 parts. I've got a 99 NBS, and I've never had to mess with blower motor resistor blowing out on that truck.

My brother had an 06 that went thru resistors often. Not sure why. I bought an 04 project SUV, and that was one of the first things I had to change. And my 2000 k3500 GMT 400 also had the resistor blown when I bought it...

Also, out of all those trucks, the 99 is the only one with a cabin filter. Not sure if that's a 99-02 thing, but at some point the cabin filter was deleted. May not matter to you though.

 

[400North]

So I replaced the resistor which got the gmt800 fan working on all fan speeds now, but the resistor started smoking right away (it smokes on all speed settings not just high). So I will have to find a wiring diagram for gmt400 and gmt800 and figure out how to wire the gmt800 resistor in.

 

[GoToGuy]

The " I don't much about electrical" at the beginning sort of explains the smoking parts. Do you have a fire extinguisher nearby, that's works?

 

[400North]

The " I don't much about electrical" at the beginning sort of explains the smoking parts. Do you have a fire extinguisher nearby, that's works?

Lol, ya I do. I disconnected the battery right away and I unplugged the resistor.

 

[400North]

So I combined the center part of a gmt800 blower motor shrowd with a gmt400 shrowd and put it back together in my truck to test it on high, it blew a bit more air through the vents but not as much as I was hoping for or not enough for me to find this modification worth it. So I’m putting this modification on hold for now, I might open up the hvac box more and see what I can find.

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