Normal operation for aux cooling fan?

Hi folks -

My 1993 Suburban 7.4L has the OEM auxiliary pusher fan installed, and I'm beginning to wonder if it's doing what it's supposed to do. I only hear it run after I get back into the truck after some in-town driving, so your typical stop-n-go stuff that will always have temps creep. I do NOT really hear it otherwise, even though I'm under the impression it should come on whenever I turn on the AC.

So, what are the conditions that are supposed to trigger this thing?

The two "issues" I'm tracking down are AC-related. First is that the AC is not all that cold at idle and around town. This may be a charging issue, but I'm looking at all possibilities. The second is that the engine temps jump more than I'd like with the AC engaged, again only when idleing and around town. Typical for my truck is around 200*, but with the AC on and in town, that will creep up a good 10* or so.

All parts of the cooling system are new, including radiator, fan, clutch, hoses, pump, and thermostat.

Mike

Tinkering a bit...

I pulled the harness off the switch located in the passenger side head. I ran some wire from it to ground, and with the ignition on, the fan started blowing. Looks like the relay up on the driver side fender near the firewall drives this guy, and it obviously works, too.

So, question still is, should it be coming on with the AC and, if so, what's supposed to trigger that?

Mike

This is the fan in front of the condenser, right?

I’ve read that those are controlled by a temperature switch on the block to engage at 225-F.

Mine does the same,I wired in a toggle switch to control the fan.It never came on when the A/C was on so I helped it a little
Taken from ALLDATA:
''When the Ignition Switch is on the RUN, BULB TEST or START positions, voltage is applied to the coil (power side) of the Auxiliary Cooling Fan Relay through the IGN E Fuse. Ground is supplied to the coil (ground side) of the Auxiliary Cooling Fan Relay through either the Auxiliary Cooling Fan Temperature Switch, High Pressure Switch or the A/C Controller. When either of the above three components provide ground to the coil of the Auxiliary Cooling Fan Relay, it energizes and the contacts close. Voltage is applied through the AUX FAN Fuse and the closed contacts of the Auxiliary Cooling Fan Relay to the Auxiliary Cooling Fan Motor. Since the Auxiliary Cooling Fan Motor is grounded at G112, it runs.''

east302 said:

This is the fan in front of the condenser, right?

Click to expand...

Yep

grampadirt said:

Mine does the same,I wired in a toggle switch to control the fan.It never came on when the A/C was on so I helped it a little
Taken from ALLDATA:
''When the Ignition Switch is on the RUN, BULB TEST or START positions, voltage is applied to the coil (power side) of the Auxiliary Cooling Fan Relay through the IGN E Fuse. Ground is supplied to the coil (ground side) of the Auxiliary Cooling Fan Relay through either the Auxiliary Cooling Fan Temperature Switch, High Pressure Switch or the A/C Controller. When either of the above three components provide ground to the coil of the Auxiliary Cooling Fan Relay, it energizes and the contacts close. Voltage is applied through the AUX FAN Fuse and the closed contacts of the Auxiliary Cooling Fan Relay to the Auxiliary Cooling Fan Motor. Since the Auxiliary Cooling Fan Motor is grounded at G112, it runs.''

Click to expand...

Ok, interesting. Definitely not coming on with anything AC-related now. I'm debating the switch approach, but I'd still like to figure out why it isn't coming on with the AC if that's what it's supposed to do...

Mike

whiteboyslo said:

Ok, interesting. Definitely not coming on with anything AC-related now. I'm debating the switch approach, but I'd still like to figure out why it isn't coming on with the AC if that's what it's supposed to do...

Mike

Click to expand...

Yeah,me too.Some day I'll get my MM out and find the problem.

Here’s another discussion on it. It sounds like it isn’t supposed to be on all of the time, but some have thought about modifying it to turn on whenever the compressor is on to assist in cooling.

https://www.gmfullsize.com/threads/where-does-the-ac-condenser-fan-draw-signal-from.192185/

east302 said:

Here’s another discussion on it. It sounds like it isn’t supposed to be on all of the time, but some have thought about modifying it to turn on whenever the compressor is on to assist in cooling.

https://www.gmfullsize.com/threads/where-does-the-ac-condenser-fan-draw-signal-from.192185/

Click to expand...

I'm definitely seeing conflicting opinions on what should cause the fan to turn on. Some diagrams I have found show that it is ONLY triggered by the coolant temp switch (nothing tied to AC), others suggest it comes on if the High Pressure switch on the compressor engages, others say that just having the AC running should turn it on.

I'm going to experiment with having the wire off the temp switch ground out using a relay. I'm going to run the relay off the AC clutch so that, whenever the clutch is engaged, the wire to the temp switch will go to ground. It's a bit unconventional because a) I'm using the relay to ground something (as opposed to powering it) and b) I'm using a relay to trigger another relay, but I don't see why it shouldn't work. I thought about just running a switch into the interior that would also ground the temp switch wire, but this seems cleaner. I also don't have to worry about accidentally leaving the fan on all the time when it isn't needed.

I bought a basic 40AMP SPST relay kit off Amazon that comes with a harness and pigtail. Should be here in a few days. I'll wire it in and report back.

Mike

Just reading along guys. I can't think of any, but just asking the question...is there any detriment to wiring an aux fan to trigger off the AC clutch instead of the high pressure switch?