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A/C blower fan upgrade

  
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A/C blower fan upgrade

 
Brazil Brazil
Addict | Posts: 3889 | Joined: 06/09
Posted: 12/10/13
07:36 AM

My bud Clint just bought a '78 Bandit in great condition down here in Texas (Baytown), and ask me about the weak A/C output.

I haven't run an air conditioner in my birds in years because they always drag down the RPM's and make the motor overheat, especially after any cam upgrade.

Clint's Bird is, from what I understand, pretty much stock. His question to me was is there an A/C fan upgrade that would push some more icey cool out the vents and upon his person.

Can y'all pass some wisdom our way on that?

Braz  

gtojack1366 gtojack1366
Guru | Posts: 1224 | Joined: 11/09
Posted: 12/10/13
07:58 AM

I don't think they make a heavy duty blower motor for the firebird just the stock ac blower motor .There's probably something wrong with his AC doors not working right .You don't need icey cool air now !Icey cool air just open the window ! Grin  Two snow storms in two days here !  

65pmdgto1 65pmdgto1
Enthusiast | Posts: 504 | Joined: 12/07
Posted: 12/10/13
08:37 AM

He probably needs to freshen up the AC control hoses, starting at the source on the engine. Then check out the switch and speed resistor. Those old actuators probably need to be checked out. After standing on his head and scraping up his hands and arms he may just put he windows down.
When all is right with these GM systems they will freeze you out. If the car has been converted to 134 it may need to have a real pro check it out. The proper charge and orifice tube make all the difference in the world.  

Brazil Brazil
Addict | Posts: 3889 | Joined: 06/09
Posted: 12/10/13
01:35 PM

All good advice Clint. The mechanical parts under the dash rust up and won't move. I take them off and use a wire wheel bench sander to make the parts shiny, followed by a little spray of WD-40. The hardened rubber on The vent door could use some light lube too.

The switch and speed resistors function much like the wound copper headlight relay coils. When they get old and corroded, the lights are not as bright. And I have also had a dude install the orifice tube backwards. all the crud that it is supposed to block was shot directly into the evaporator.

I agree that with the nice Trans Am you have aquired, some pro air place would be a good move. Right now A/C is called lowering a window ever so slightly.  

wayne712222 wayne712222
Moderator | Posts: 165 | Joined: 10/13
Posted: 12/10/13
02:33 PM

i would probably make one modification to any GM AC system from the mid 50s up thru the late 80s..

i would add an on off switch to cut off the ac compressor clutch power with a load dropping relay.. .. 30 amp ice cube relay..

pin 30 and 85 from the car wiring to the compressor..
pin 87A to the compressor clutch
pin 86 to a switch.
the other side of the switch is grounded..

in almost all the manual systems and most of the digital climate control systems that came out in the late late 70's and early 80s.. they keep the AC compressor running and cycling when you are also calling for heat..   this give the system the ability to  control the temp to anything you want.. and is a great idea.. except for the fuel economy issues... some cars had a switch like a TH400 kick down switch that actually cut off the ac compressor near wide open throttle..

each year is wired and switched slightly different..

while i had the dash apart.. i would also want to closely inspect the blower switch and the clutch control switch which is a flat rotary device on most of these in the late 70s.. as the contacts burn slightly when they make and break the power to the clutch coil.

i think i have a manual that covers HVAC on late 70s cars.. i will have to look thru it.  somebody gave it to me.. i never opened it but once or twice..


there is one more thing..  there are various fractional horsepower differences in the defroster fan motors between models..  but there is no listing of which ones make more power..  picking the proper one for the application is probably the best..
or ordering a NOS GM version or hopefully a DElCO version.. might get a person something better than the generic small Hp cheep fan motor.. one size fits all..

in my personal opinion i would look for heater/defroster fan motors from big caddy, full size wagons.. suburbans..  if you want the biggest blow for the buck.. wow.. that makes me sound so cheep..  i already give this away for free.  

idrivejunk idrivejunk
Addict | Posts: 4991 | Joined: 12/09
Posted: 12/10/13
05:54 PM

Hi Braz, Clint. Sounds like a nice one. Lots of late model stuff has plastic "blades" (aka squirrel cage or hamster wheel), I wonder if maybe late S-10s or F-bodies had something plastic the right size to swap. Is the blower fan a metal one now? Possibly a lighter weight fan could gain a few RPM or power for ya. I'd bet later motors turn faster too, the controls vary a lot but the motors usually just have + and -. Maybe a guy could add a small fan like for a PC case, to the box somewhere. But absolutely yes, the blend / defrost doors gotta be working to get a good huff out of 'er. And that means the vacuum switch and diaphragms and everything its got. Plus all those old foam seals around the box that get chunked when the heater core blows out and soaks em down, those can make a large difference.  
idrivejunk

gtojack1366 gtojack1366
Guru | Posts: 1224 | Joined: 11/09
Posted: 12/10/13
06:48 PM

There might even be a mouse nest in there ! I've found that before in a 84 el camino . A big pile of seat insulation ! Cleaned out then had tons of air flow !