Welcome to the Corvette Forums at the Corvette Action Center!

News: A/C switch lessons - early C4

WhalePirot

Well-known member
Joined
May 9, 2002
Messages
2,942
Location
SoCA
Corvette
1984 White Z-51/ZF6-40/Shinoda body
Here's what I learned:

My '84 is an early production, Z51 car; January. HotRodRoy's is a month later. The A/C in mine has been inop and mostly removed for years as mods were done, then refined. Recently, things went so well, under ZFDoc's care, that I had new A/C components sent to him for installation. It blew "ice cubes", he said, with the newish R12a gas for many days, then seemingly did a pressure discharge; no more cold and a cycling compressor!

The new compressor (Rock Auto) had no switch on its backside as the old one had, which started my search for what it was (the old one was broken/gone). I was told by one of the best local experts, that a replacement switch could replace an aluminum plug held in by a snap ring and sealed by an o-ring (wetted with refrigerant oil). My local parts guy said it was a certain switch, which I installed. Nope; wrong switch!

I called the outsourced tech help for Four Seasons, polite but no help. However, a Four Seasons product manager (Mark) called me with real info (also a polite car guy). They sell many switches that appear the same, but the differences extend past their color, which indicates what they are: normally open (N.O.)/normally closed/(N.C.), activation pressures, etc.

On my car, that switch (sensor) closes (grounds) when the pressure builds in the compressor when switched on thru its clutch. It is a normally open (N.O.) switch. Compressor activation, therefore, switches the single fan on, as does the engine temp. (ECT) switch via the same relay.

There ISN'T a High Pressure safety switch to deactivate the compressor, in case the system's pressure gets too high, on my car. That switch is in series with the low pressure switch, and IS on Roy's car. It is a 2-terminal switch in the outboard (H.P.) port on the hose fitting attached to the rear side of the compressor. (Another setup I have for my Corvette-powered F100 has none; supposedly from an '87.) I won't put words in Roy's mouth but, while the why of one car having and another not eludes us, Chevy felt my car didn't need one. Actually, the A/C worked well for many years without that switch.

The switch I (wrongly) installed was a high pressure safety; tested closed right from the box (NC= normally closed). The 'tech dude' said it was defective, but a replacement tested the same. In fact, it was operating properly, but was the wrong part#, which became clear in the product manager's call. He had access to wiring diagrams and more product detail.

The fan-relay-activating, N.O. switch tests as it should, normally open with no pressure. It is purple, not light blue, but otherwise appears identical to the HP safety switch (N.C.).

I asked the product manager about the (C4) system I am installing in the F100. That 'wrong' switch can serve its HP safety function if installed in that port on the compressor (the plugged hole). I am doing the truck's wiring, so it is a simple matter to have the fan activate (C-4 single-fan) when I switch on the A/C.

I hope this helps someone (and is clearer than my initial post). :w
 
Last edited:

WhalePirot

Well-known member
Joined
May 9, 2002
Messages
2,942
Location
SoCA
Corvette
1984 White Z-51/ZF6-40/Shinoda body
It was rather easy to install the switch, shown here:
IMAG0748.jpg

Once, that is, the rubber hoses were out of the way. :w

That yellow thing is a bright LED flashlight that has a magnetic clip for pockets and other things. It also swivels and is one of the handiest lights I own.
 
Last edited:

Hot Rod Roy

Well-known member
Joined
Jul 6, 2005
Messages
317
Location
Mission Viejo CA
Corvette
Yellow '84 Coupe
Just to be clear, Mike, you do realize the switch shown in your photo is the "a/c pressure switch" shown on pg. 8A-149 in your elect. manual, and is the switch that activates the radiator fan relay when the a/c is turned on (presuming your a/c is operational). This must be a N.O. (normally open) switch.

This is not the "high pressure cut-out switch" shown on pg. 8A-130. The "high pressure cut-out switch" must be a N.C. (normally closed) switch.

:pat
 

navy2kcoupe

Well-known member
Joined
Dec 16, 2006
Messages
799
Location
West Central FL and SE Mass.
Corvette
2000 Navy Blue Coupe A4 Z51
That yellow thing is a bright LED flashlight that has a magnetic clip for pockets and other things. It also swivels and is one of the handiest lights I own.
Got 1 of those myself, only in blue, and it's PHENOMENAL! :thumb
Andy :w
 

WhalePirot

Well-known member
Joined
May 9, 2002
Messages
2,942
Location
SoCA
Corvette
1984 White Z-51/ZF6-40/Shinoda body
Just to be clear, Mike, you do realize the switch shown in your photo is the "a/c pressure switch" shown on pg. 8A-149 in your elect. manual, and is the switch that activates the radiator fan relay when the a/c is turned on (presuming your a/c is operational). This must be a N.O. (normally open) switch.
Yes, on the Corvette. The second replacement switch is N.O.

This is not the "high pressure cut-out switch" shown on pg. 8A-130. The "high pressure cut-out switch" must be a N.C. (normally closed) switch.:pat
Thanks, Roy. I got it. I am using that (the first switch I bought) as intended, on the F100's Vette driveline and will wire it so the fan (C4) runs when the A/C clutch is activated. :w
 

Corvette Forums

Not a member of the Corvette Action Center?  Join now!  It's free!

Help support the Corvette Action Center!

Supporting Vendors

Dealers:

MacMulkin Chevrolet - The Second Largest Corvette Dealer in the Country!

Parts/Accessories:

Vetteskins

Advertise with the Corvette Action Center!

Double Your Chances!

Partners

Top Bottom