dunno513

'89 single fan. Fan comes on with engine temps at 226 an off at 213. But it does not come with AC causing over pressure on the high side. Diagnosed AC today, no blockages everything clean, vacuumed and refilled. While driving AC works fine. Stop and the high pressure cutout cycles the compressor.

Would a bad fan relay work for the engine temp, but not for the AC ?

Already pulled the AC high pressure connector and jumped it. All that seems to do is cycle the clutch, no fan.

Even replaced the unit on top of the Evap box (had a spare), not that.

Just wondering where to dig next. Dive into the ECU?

my aftermarket SM doesn't seem to address the single fan units so I'm at a loss.

AGENT 86

Maybe the wire from switch is shorted to ground ?

Cliff Harris

The ECM has an input from the A/C so it knows that the A/C is on. The ECM controls the fan, so if the fan is working then the A/C switch is your problem (or the wiring/fuse associated with it).

Hooked on Vettes

Assuming you have the C68 Auto Climate Control.

The AC Coolant Fan Switch which screws into the high
pressure line Opens around 233-240 psi and Closes around 185-
190 psi.

The Switch has two wires going to it. A Dark Green wire
goes to the ECM. The Black wire is ground.

If you unplug the connector, (simulates over 233 psi), start
the engine, the Radiator fan should run.

If the Fan does not run, there is a problem with the ECM.

If the Fan runs the problem must be the AC Coolant Fan Switch
is closed all the time, the system pressure is never reaching
240 psi which would open the switch or the Dark Green wire is
shorted to ground.

If you remove the plastic wheel well housing you can get
a better look at the Fan Switch.

The switch next to it towards the firewall with the larger
connector plug is the High Pressure cut out switch.

For safety reasons, there would be no reason to short that switch
out unless for testing purposes to see why the AC Clutch won't engage.

The schematic also shows the auxiliary fan which you said you don't
have.

SunCr

I only recall 1 wire to the switch, but it's getting a battery reference from the ECM and since the switch is normally closed (grounded) the ECM sees 0 volts. When the switch opens at the parameters outlined, the reference rises at the ECM and when it sees that, the fan should crank on. You similate the open by disconnecting the harness from the switch. If that turns on the fan, the ECM and wiring are good. Before you run out and buy a new switch, check operating pressures to make sure it's making the psi it needs to open it up. Low gas or ambients below 60 at the Condensor probably won't get it there.

dunno513

Thanks for the responses.

I thought that the sensor closest to the firewall on the high pressure line was the High Pressure AC Switch.. not the Cut Out. I will have to check the second one closest to the front of the car.

After that I will check those wires for grounding, replace the AC control unit then the ECU.. I happen to have some spares kicking around which is helpful.

Last time I replaced an ECU I came in from the bottom under the dash.... is it easier to come in from the top with the dash panel removed?

Hooked on Vettes

According to the factory diagram it is. On my 89 it's the opposite of
the diagram.

So the factory probably just installed either switch in either position
since the plugs are so close to each other.

To identify which is which.

AC Fan switch Dark Green wire and a Black wire. Small plug
High pressure cut off Light Green wire and a Black wire. Larger plug.

Remove the foot well panel that contains the courtesy lamp. Disconnect one electrical plug that crosses under the ECM. Remove two nuts
and the white plastic bracket will drop down along with the ECM.

Here's the AC fan switch operation.

dunno513

Yup, it's the sensor. And yup... they're backwards. When disconnected fan fires right up. Whew.... I really did not want to replace that ECU.

So now the $30 question.... Am I going to loose all my r134a replacing that bugger? I'm assuming that since I have seen over 400 psi on that line more than once and never saw the fan kick on... the switch is a guaranteed bust.

And one final note to anyone replacing the metering valve... Don't put the valve all the way down into the tube first.... Put it half way in, then make sure the tip fits into the top tube. Otherwise it bends it over when tightened...

Hooked on Vettes

Manual doesn't say if the Fan Switch has a schrader valve underneath.
Does show it uses an o'riing.

Only mentions the Low Pressure Cycling Switch has a schrader valve.

Buy the switch and see if has something to depress a schrader valve.
If it doesn't you need to remove the refrigerant.

GM part #14078970
Delco part #15-2351

This Fan Switch was used on vehicles from 1985-1993.

dunno513

There is a valve.

Used one from the donor car is also bad so its off to get a new one. Are these a common failure item? Wierd I have two cars and they are both bad.

Amazon has the best price, but for $5 more I'll go NAPA so I can have it today.

Thanks for the part numbers.

edit.

Spoke too soon.. NAPA quoted me the wrong switch and was almost twice the price so Amazon it is.

SunCr

I'd check pressures - 2 switches bad? Switch is still a Dealer item - bought one for a Member a year or so ago.

ch@0s

Wow! this thread is full of great info you guys rock.

dunno513

Correct $25 switch from Amazon arrived Friday. Back in business.


Thanks to all.

Theatrepc

Hi guys.. hoping for some help here. I bought a 1976 stingray and when I first got the car the blower fan for the a/c would only come on if I was driving. When I would idle at a light, it would turn off.
Now it doesn't come on at all. I have replayed the blower relay. Replaced the blower resistor. Replaced the interior climate controls, fan switch..

Now when the engine runs, I hear and feel the compressor kick on when the switch is set on high. But the fan still does not come on. What am I missing?

Thanks,

Rob

Cliff Harris

What you're missing is that this is the C4 forum. This belongs in the C3 forum.