Ac condenser fan

[57taskforce]

Can anyone tell me how the 96-0whatever vortec 454 factory auxiliary electric condenser fan is supposed to work? I’ve recently put my 98 back to daily driver use and have noticed it’s not kicking on the same as it used too. I’ve only noticed it running once lately and my idle/traffic ac vent temps are close to 60* when cruising they are at or slightly below 40* with it close to 100 outside. The ac charge is not the issue. When it gets to about 210 the mechanical clutch fan will kick in and the ac will get cooler. I seem to remember that auxiliary fan mostly always being on when the ac was on in the past but I really haven’t driven the truck really much at all over the last 9 years so maybe I’m remembering wrong.

[Richard]

A couple of pages from my recently acquired Chilton manual. In diagram 27 it looks like the fan can be activated by both a temperature switch and an A/C switch.

[57taskforce]

Thanks Richard. That does help confirm some reading I’ve done. Im pretty sure on the vortec stuff the PCM actually commands the fan based on those two inputs you mentioned… or so the internet says…

I jumped the ac high pressure switch earlier today and the fan came on right away, so maybe my pressures aren’t as high as is necessary to close the switch. I did some research and it should have a 300lb switch in it. I know the temps likely don’t get high enough to trip it as it never really goes over 210. It supposedly should turn the fan on around 225… again or so the internet says. On the freeway at 60-70mph the vent temp is about 38*. I guess I’ll leave it be for a bit and see what happens.

[Ol Blue K20]

I'm kinda sure my 95 is a bit different. But, I'm having the same issue. Keep us informed and maybe I can figure mine out.

[Richard]

Wish I could help more. My 94 does not use the Aux fan. Would start by finding the A/C switch controlling the fan relay. Have no idea if pressure, mechanical or electronic.

[Richard]

Was thinking, you said you jumped the high pressure switch and fan came on. The high pressure switch would be normally closed and open on high pressure to shut off compressor. Jumping out the high pressure switch would not do anything on a pressurized system. Thinking the switch you jumped is the fan switch.

Edit- My 94 uses the R4 compressor. Well, used to as I converted to a Sanden. The high pressure cut off switch is mounted in the back of an R4 compressor. The cycling switch will be in the high pressure line and low pressure switch in the suction line.

[57taskforce]

I was actually thinking along these lines as well, maybe the high side has two switches because when I jumped the switch on top of the compressor where the high side line exits the compressor it kicked the fan on but the compressor didn’t stop like I had expected it too. I had the grill out of it yesterday morning and didn’t see any other switches but it’s tight down on the passenger side of the inner fender and core support where the lines come thru to the condenser so I could have missed it.
I had mostly just assumed that the cycling switch and the aux fan both of which would be in the high side, were one in the same and the computer just did what it was programmed to do with the signals received from the switch. Maybe I’m wrong here.

After reading over the schematic above more, I’m a little confused. I definitely didn’t jump an engine temp switch, and it doesn’t show the high side pressure switch having anything to do with aux fan. I certainly did jump the high side switch.

And… in this case that particular high pressure switch would almost certainly have to be a normally open switch so when it hits the prescribed pressure it closes, completing the circuit to the computer or relay… unless the pcm is looking for a lost hot or ground reference I guess. Now I’m gonna have to see if the pigtail is hot or ground on one side just because I’m curious.