Hooking up Electric Fan to AC

[JP422]

Hey guys.. I know some of you have electric fans... and some of you have manual overide switches to turn them on... but has anyone hooked up the AC turn on line successfully to the AC?

I have the PermaCool fans.. (they're awsome) and wanted to hook up the AC turn on wire (blue wire) from the Fan controller. Instructions say to hook it up to the pressure switch on the Drier. That's simple enough... so I tapped it into the green wire on the pressure switch (the switch has 2 wires... a blk/wht, and a green... this green one was recommended by another guy).

I believe my AC system works fine... I just had it recharged a couple days ago, and the new Sanden compressor works fine... but I had to manually turn on the Efans (attaching (+) power to the blue line) when the shop was charging the system. It blew nice and cold.

I tried hooking up the blue line to the drier switch last night, and the fans would not turn on when the AC was on... and the AC clutch was spinning fine too. This is not good. I tried unplugging the connector from the pressure switch, and then the fans turned on.... and the AC compressor stopped.
What gives... is my pressure switch bad? (my AC works ok).

Has anyone had any luck hooking up the EFans to activate w/ the AC compressor?

I plan to hook up a manual switch eventually, but would like it to turn on w/ the AC automatically anyway.

Any luck here?

 

[95TwinTT]

Hey guys.. I know some of you have electric fans... and some of you have manual overide switches to turn them on... but has anyone hooked up the AC turn on line successfully to the AC?

I have the PermaCool fans.. (they're awsome) and wanted to hook up the AC turn on wire (blue wire) from the Fan controller. Instructions say to hook it up to the pressure switch on the Drier. That's simple enough... so I tapped it into the green wire on the pressure switch (the switch has 2 wires... a blk/wht, and a green... this green one was recommended by another guy).

I believe my AC system works fine... I just had it recharged a couple days ago, and the new Sanden compressor works fine... but I had to manually turn on the Efans (attaching (+) power to the blue line) when the shop was charging the system. It blew nice and cold.

I tried hooking up the blue line to the drier switch last night, and the fans would not turn on when the AC was on... and the AC clutch was spinning fine too. This is not good. I tried unplugging the connector from the pressure switch, and then the fans turned on.... and the AC compressor stopped.
What gives... is my pressure switch bad? (my AC works ok).

Has anyone had any luck hooking up the EFans to activate w/ the AC compressor?

I plan to hook up a manual switch eventually, but would like it to turn on w/ the AC automatically anyway.

Any luck here?

The switch with the blk/wht and green wire is the A/C cycling switch. I think you want the low pressure switch. That one has lt grn and dk grn / wht. The best one there would be the lt green. That should give you fans on with the A/C running.

 

[JP422]

Interesting... Thanks for the input ..again!

eh.. but excuse my ignorance on this... but where is the low pressure switch? Is it the on the back of the compressor? When I called PermaCool, the guy just said he hooks it up to the pressure switch on the drier. Is there another switch on the drier, becasue I only see one (which is the cycling switch)...

Thanks!!!

 

[95TwinTT]

I was going by the wire colors called out on the schematic. I went out and looked at mine and I’ve got orange and green on my pressure switch. I don’t know what GM is doing with wire colors here.

I’m pretty sure all you are looking for is a +12 when the A/C is on. Just take a VOM or test meter and see if you have that voltage at the wires on the one of the wires plugged into the tank like device next to the firewall, passenger side.

With everything off, the pressure switch should have continuity. Mine has a vacuum line going to the cycling switch, but it too is connected to that tank.

You don’t want the fans going on and off with the clutch, so the cycling switch should be avoided.

The schematic also shows a auxiliary cooling fan relay in the under hood fuse-relay center. It might be worth looking to see if it is populated with a fuse and relay. It says it has a 30 amp mini fuse on the schematic.

Let me know what you find……… :cool2:

 

[JP422]

that was one of my problems... my mulitmeter went bezerk last night, so I had no readings... Gotta get a new one.

Anyway, I'm confused about which is a cycling switch and which is a pressure switch (on the AC drier .. the canister cylinder thing on the pass side firewall..right?). I only see one electrical sensor...

Some guys even say to just wire it to the AC compressor clutch... and I'm positive this will cycle it w/ on-off like you said... Am I missing something here? Who woulda thought this would be so complicated?

The PermaCool tech also mentioned that GM changed the wire colors often, so he couldn't keep up w/ all the wire color combinations... so he just said to wire it to the drier. This doesn't help much.

I don't understand why the green wire from the drier switch will show (+) when disconnected and be able to trigger the fan... but not trigger the fan when the connector is plugged back into the drier. I'm tempted to get a new sensor or whatever the thing is on the drier), but that also measn I have to recharge the AC system again...

Anyway, I hope I can figure this out... it should be much simpler than all this..

 

[95TwinTT]

There are three separate switches on the freon system. Low Pressure cut out, high pressure cut out, and compressor cycling switch. Two of those switches have one pin hooked to ground. They should also have at least one black wire, hopefully the ground wire.

The switch that you want is the Low Pressure switch. As I look at the schematic, I would think that with everything turned off, you should be able to identify the Low Pressure switch, by pulling the plug off the switch and check both sides to ground with a VOM. It should be open on both pins. Both the other switches, the A/C compressor cycling switch and the high pressure cutout will both have one pin showing continuity with ground.

After identifying the low pressure plug, turn on the ignition with the A/C on and see which side of that plug shows + 12 volts. That is the wire you want to splice into for the fan switch.

 

[JP422]

Thank you for the thorough instructions... I'm gonna pick up a new mulitmeter and give it a try tonight!

 

[JP422]

OK... done!

I picked up a new multimeter from RadioShack... The ones that fold up in a case and fit in your pocket... (man, these used to be $10-15 back in the days... now it's almost double that... but I was desperate). Anyway I got some more tips... and my curiosity got me.. so I ended up stripping back small hidden sections on the sensors to test them... (while they were plugged into the sensors)

-The sensor on the AC drier (which turns out to be a cycling switch). Green and Blk/wht. The PermaCool tech told me he taps into this sensor...but it's wrong.

-The pressure sensor on the AC piping near the AC compressor (low pressure switch?) I also tested these wires, and they didn't activate the fan either.

-I skipped the high pressure switch on the back of the AC compressor because it was hard to reach, plus I felt like I'd get the same results.

-The AC clutch wire was my last resort... and sure enough... it worked perfectly. When the AC is turned on, then it will feed a (+) and (-)... so just find the right one (I believe the pos wire was blue... I was working under poor lighting so that's what it looked like to me). Interestingly, the Blue fan activation wire has a shorter path running to the AC compressor than to the Dryer on the firewall.

All the wires were taped up, covered in loom, and zip tied for a nice clean appearance. One day I'll add a manual turn on switch as well.
Now the fan works just as it should, and AC is ice cold. Hopefully this is the last of working on the AC system!

Thanks for the tips and advice!

-Joe

 

[95TwinTT]

Sounds like your Tahoe has the correct wire colors. Congrats on getting the Perma Cool’s hooked to the A/C.

I wonder if you could check something on your truck? The schematic leads me to believe that the low pressure switch has +12 volts on the lt grn wire. Since it did not work to turn on your, fan, I’m wondering if it is actually 5 Volts.

It goes from the heat and A/C control module, through the Low Pressure Switch and then to the VCM on the dk grn/wht wire.

The schematic does not call out voltage, it only shows connections. It would be good to add some notes to the schematic……..

I went out to check this on my Tahoe and I don’t have the same setup. I’m missing the high pressure switch and my low pressure switch goes to ground.

The schematic say’s 1995 and later, they must have meant 1996 and later, with OBD-2. Thanks…….

 

[JP422]

TwinTT... thanks for your input on this issue. As for the wire you as for, here's what I noticed.

First off though, I'm a grease monkey, love wrenching, but not very familiar w/ all aspects of an AC system. I do have lots of reference, and schematics too... but the GM schematics seem to be the most vague or have the most variations.. which drives me nuts. They end up just being guidelines to what I'm after.

This truck is the deepest I've gone into an AC system, and mostly w/ what I learned from the internet research... and schematics.


Here's some things I noticed:

-The low pressure switch (the one on the alumnium pipe near the service ports) never gave me a (+) reading. This baffled me, and I tested both wires w/ a multimeter, and w/ the Fan activation wire. I tested it w/ no key, then w/ key on... then w/ AC on. Nothing. It could have been that the probe touching ground might have been bad (my back was aching after crouching over the fenders on a foot stool), but it still didn't trigger the fans. As for your 5V theory... I can't disprove it, but my multimeter didn't read any (+) voltage this time.

-The cycling switch was interesting. (the sensor on the AC Dryer). When hooked up to the green(?) wire, unplugged from the sensor, then it reads (+) when the key is in the ON position regardless of AC on or off. But when I plug the wire back onto the cycling switch, then the (+) is gone... (grounds out?).

-The AC clutch plug was easy. No voltage when key is on... but once you activate the AC, then a nice healthy 12v (+) turns on (and a ground on the second wire).

-I couldnt tell you if there was a 5V signal.. but your throe does make sense too... however, so far in my quick and dirty testing, I never saw any steady 5V anywhere.

-------------------------------

As for more things to think about... this was a quote from PSWired from another forum:

"The older systems ran the current for the compressor clutch straight through the cycling switch on the drier (or maybe it's the relay trigger voltage, in either case it's a +12 signal). The newer systems have one side of the cycling switch tied to ground, then the other side goes to either the PCM or HVAC module depending on application. The module sends a sampling current down the line and senses when the switch is closed, then activates the AC relay as necessary. Looks like they had changed to the new system by 99."

 

[95TwinTT]

Thanks for the info. I think I will get rid of this book of schematic’s. It is not much good if it is only correct part of the time.

I must have the older system that grounds the +12 for cycling. I’m using a aftermarket computer to run everything, so there is not much stock wiring left in my Hoe.

Thanks again for the feed back.