84
So I've needed to replace the AC pressure switch on the compressor. (this is held in with the o-ring and snap ring,just so we are on the same page)
The 84 is a grounded circuit switch, 1 wire.
The new switches seem to be all 2 wires and everyone I got is a normally closed sensor. Per the instructions 1 wire goes to the original sensor wire and the second wire goes to ground. Well what happens is when you turn the key on... the radiator fan turns on and won't shut off.
So I'm going to try remove the ground wire under the assumption that the fan will turn off since its not completing the circuit right away.

Since these switches are normally closed and the FSM says it closes when you turn on the AC can someone explain to me exactly how this works?
thanks

 

I think what you have - or your Parts Supplier is selling you - is a High Pressure Limit. Source is from the Panel, through the Switch, and onto the Compressor Clutch. Normally closed, it opens above 400 psi and kills power to the Compressor. That's why there's a 2 pronged terminal, the circuit - hot - is completed through this Switch. The Fan Switch simply opens/closes the ground side of the Fan Relay. It's grounded through the Compressor Body (then engine to chassis). It probably closes somewhere around 220 psi and that kicks on the Fan and opens once the pressure drops below 200 psi or so. It only needs the single wire. Finding the right one may be problematic; though you want the fan to cycle within a range to maintain an ideal flow of liquid into the Evaporator. If the Fan runs all the time, the charge will cool to the point that the Compressor cycles off/on raising vent temps and causing excessive wear on the clutch components.

 

Poked around a bit and see that you've tried my friends at www.ackits.com though you might call them. I don't see a replacement anywhere. Even Corvette Central is offering the later years (for an '84) which threads into the high line and that's a normally closed switch which opens (you want something that closes) at 230 psi signalling the ECM to trip the Fan Relay. These switches are 2 wire because the line doesn't provide much of a ground for the signal. The only other thought would be to communicate with the C3 folks. I think the later years used the R4 compressor, but I don't know if they had electric fans.

 

Thanks for the reply. The only thing offered is this http://shop.advanceautoparts.com/web...ressure+switch

I as well have searched all the part stores online and can't find an exact replacement. Since this is N/C and not N/O my assumption is it won't work correctly?
I was also under the impression that this allows the coolant fan to turn on when I turn my AC on. Is that correct? or does it cycle the fan thru the pressure it reads?
There is a AC cycle switch that is two prong and threads onto a Schrader that goes into the High Side. But that is not connected to the Fan Relay in any way according to the FSM.
thanks

 

That looks like a High Pressure Limit.

There is a Low Pressure Limit on the Evaporator Outlet or the larger, upper line leading to the Accumulator. It cuts power to the Compressor when the pressure drops low enough for the Evaporator to ice over. Normal wiring (on most manual) a/c systems is from the a/c fuse, to the controls, to the Low Cutout, to the High Limit, to the Compressor Clutch. Clutch ground is from the Coil to Chassis.

Coolant Fan, for the later years is controlled by the ECM. 12 volts is sent to a normally closed switch on the high line. It opens at 230 psi, so the voltage signal rises at the ECM and that signals the ECM to drive (ground) the Fan Relay. It'll reclose at around 190 psi. These switches have 2 wires as there isn't a reliable - if any - ground in that line.

As best as I know, the '84 used a switch in the compressor to control the Fan. Normally open, it closes and completes the Fan Relay ground at 230 psi. That turns on the Fan. Absent a/c, the Fan is controlled by a switch in the Right head which opens/closes ground based on Coolant Temp.

Fixed cycling (orifice) systems require a high side pressure that averages around 200 psi to keep the Evaporator at anywhere from freezing to something in the mid 40's. Cycling the Coolant Fan achieves this at idle and low speeds. You're going to need something that will do this absent the ECM; ie, a switch mounted somewhere on the high side which will open/close the ground side of the Fan Relay.

At this point I'd check with one of the Vette Boneyards. Hopefully, they haven't sold all of their old R4 compressors to the aftermarket and they can send you one intact for a cheap price (hell, new is never more that $250, so I can't imagine a big price on a used R4). You could also x-reference usage for '84 - www.acdelco.com. GM used the R4 on a ton of stuff back than and any Buick, etc may have had the same set up (though maybe not given the scarcity of this Switch).

 

As you can see from the diagram, this is why I'm questioning its operation

Last year the entire AC system is completely new, no used or rebuilt parts. I damaged the connector for the High pressure sensor on the compressor, so that's why i'm replacing it.

The thought just came into mind. Maybe because the AC system is empty the pressure switch when wired up with both wires thinks it needs to be on.

 

Son of a ..... gun! After searching ACkits archive I came across a delco part number for the switch... then was able to track down the part from napa

http://www.napaonline.com/Catalog/Re...Dp%3d3%26N%3d0

For future use for anyone looking for the switch
Napa
Item#: TEM207087
Price: $21.69
tax and shipping not included
Attributes:
# of Terminals:1
Pressure Rating:150 PSI Close - Normally Open
Thread Size:Compressor Mounted


AC Delco# 15-2235

 

Fantastic! Couldn't find it there myself, but it simply supplies a Ground to the Relay. Unfortunately, I think you will need to discharge to replace it. Also, a 150 psi threshold for fan operation is a bit low for R12; but not bad for R134. OEM specs may be in the Fan or A/C Sections of your Manual. If the system is empty, the compressor won't engage as the Low Pressure Switch Contacts will be open.

 

The GM/OE from '84 is 2724279 and NAPA shows the number you've mentioned as a "change" & should be correct. If you don't do well I believe I can supply you with a couple dealers with stock still on the shelf.

 

Thanks.. I was able to get one ordered today from Napa. Now since I have a few of the correct part numbers I can find them. Most are being used on 99-03 chevy trucks.
Anyone looking to replace the one in the 84.. BE CAREFUL when going to the local stores..even Napa. They will sell you the 2 wire since that is what there computers are telling them the correct part is. Its not. Just a FYI

 

I realize this is an old post from 2013, but I have the same problem and my local NAPA show the single wire but when they use the number to order, it was the two wire, they said it was the replacement and would work..I cannot find the single wire at any store, guess I'll waste my $$ and try this two wire, but sure would like info on how/where to purchase the original single wire.

Thanks !!!

 

You can take the OE # 2724279 to your local GM's or AC jobbers to see if they have any "old stock" and a GM dealer could likely locate a dealer with the "old stock" if you wanted.

 

Ill give that a try next week, I did replace the NAPA switch today and tried to replace my freon but it was so cool here it only took a few ounces and the compressor wouldn't start I think due to low freon. I'll wait till it warms up here in Michigan and try again.

Gary