greetings all! - it's been a while!

to the point in the absence of my helms manual;
1988 vette,
auto,r-12,
electronic a/c control "panel", etc........

...if at any time i turn on the a/c are not the fan(s) at the condenser to come on regardless of the temps inside or out?....i seem to recall that they do. fans (***both***) test to be good.

....no problems with the refrigerant charge, h/l pressure switches, and compressor runs fine.....i am noticing that the fans (condensor) aren't coming on when i switch the ac on in a "cold ambient temp"....i did however substitute a good known relay near drivers firewall for the fan(s) with no change........THANKS.........**NOTE;to clarify - when i activated the fan(s) manually, they came on at that time. I did not suspect that the radiator fan was INTERMITTENT and on it's last legs...go figure!

 

One of the fans is supposed to turn on anytime the compressor is running.

 

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.....thanks for the reply.....yeah, i realize that (i thought so) but, what could be the culprit in this....i do not have helms handy....

 

The ECM monitors the AC Coolant Fan Switch that's mounted on the high
pressure line near the evaporator box under the hood.

The AC Coolant Fan Switch closes when the high pressure line reaches 240 psi. The
The ECM will then turn on the primary fan. When the pressure drops below
190 psi. the ECM will turn the fan off.

The auxillary fan is controlled by a Fan Switch screwed into the side of
the driver side head. The auxillary fan is turned on when the engine temp.
reaches around 228 degrees F.

 

I had the same issue on my '89 which has an '88 air conditioner. This was the fix:

http://shop.advanceautoparts.com/web..._435429008____

Find this switch on your high pressure line. Unplug the connector and see if your fans come on. Then you will have your answer- need to replace this switch.

 

Don't worry about having to evacuate and recharge when replacing this switch. The line has a schrader valve under the switch.

 

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**THANKS FOR THE REPLY**

The ECM monitors the AC Coolant Fan Switch that's mounted on the high
pressure line near the evaporator box under the hood.
**YUP, I KNOW WHERE THAT IS

The AC Coolant Fan Switch closes when the high pressure line reaches 240 psi.
**THE FANS SHOULD COME ON AT AN INSTANT WHEN THE AC IS TURNED ON...THERE WILL BE NO WAY THAT THE PRESSURE WOULD REACH THAT POINT IN A SPLIT SECOND...I THINK THERE MUST BE SOMETHING THAT NEEDS TO DROP TO "GROUND' WHEN A/C SWITCH COMES ON..AS IT STANDS, IT SHOULD TAKE A MIN OR SO TO REACH HE PRESSURE YOU HAVE MENTIONED.


The ECM will then turn on the primary fan. When the pressure drops below 190 psi. the ECM will turn the fan off.
**WISH I HAD MY MANUAL PRESENT!

The auxillary fan is controlled by a Fan Switch screwed into the side of
the driver side head.
**YES, I KNOW..TESTED AND IS OK..CAN SHORT TO GROUND AND FAN WILL RUN.

The auxillary fan is turned on when the engine temp.
reaches around 228 degrees F.
**THIS TOO I KNOW.I HAVE A MODIFIED SET-UP THAT BOTH FANS WILL COME ON AT 180* SO, I WILL DISMANTLE THAT SETUP AND RETURN TO STOCK 9EXCEPT FOR SENSOR) AND SEE WHAT HAPPENS THERE ALTHOUGH, I DO NOT THINK THAT IS TEH LOCATION OF TEH PROBLEM...

 

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thanks for the reply..yes i know..have done a lot of ac work and on this vehicle and hold a universal license...they make an excellent tool to extract a defective shrader w/out losing charge - one of the better tools i have purchased.....if you are referring to the pressure switches, those check good....

 

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thanks for te reply...geez, i answered the other reply first.ha!..at any rate, i will re-check this switch again.....

 

Here's the schematic for a 89. 88 should be similiar if not the same.

 

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finally getting back to this....still have the same problem as of today...i have checked any fuses pertaining to the main cooling fan and it is good (i even subbed a known and checked good one) and i have replaced WITH KNOWN GOOD RELAYS all relays pertaining to the main fan...

....as you well know, there is a very confined space to work in and in looking at my helms today, it is virtually the same as in your diagram posted...

....there is a relay on drivers fender well in front of the battery..plugging and unplugging it will activate the primary coil inside same HOWEVER, that only tells me that the relay is closing and not the condition of the contacts inside but, does not tell me if any voltage is reaching the fan.....

...i have noticed that if i give the fan a physical "push", it will start to spin, not fast as it is supposed to, but, will spin....in some dc circuits that usually indicates a current/capacitance problem (much resembling a start capacitor problem on some devices when the capacitor is bad) and, could possible be a similar (current starvation) problem here since the main doesn't use a capacitor to start....

....i have looked for the fusible link (fusible link "D" upper left in diagram) as in the schematics but, damned dark in there and cannot seem to locate with any degree of certainty although some found!.....

.....SO, what i was looking for is some direction as to where i can measure the voltage easily that goes directly to the main fan or, output terminals (or similar) from a relay going to same (needing wire color code and location), so that i do not have to spend part of a day pulling the fan to test it....

i know that there is a aldl that i can short to activate fan but, i do not believe that will help much as there has to be components between that and the fan...follow?.........THANKS.

 

I'm assuming you're troubleshooting the Main fan not coming on?

The Main fan relay is the one mounted on the driverside fenderwell in front
of the battery. The wires going to the relay socket are as follows.

Dark Blue has 12 volts when the ignition is in Run or Start.

Dark Green/White wire is grounded by the ECM to energize the relay. (Such as when you
short A to B on the Diagnostic connector and turn the ignition On).

Red wire comes from fusible link D and has 12 volts at all times.

Black/Red wire goes to the fan motor. When the relay closes, 12 volts from the Red wire then goes to the Red/Black wire causing the fan to run.

If you remove the Relay from the socket, you can take a paper clip and short the
Red wire to the Red/Black. The fan should run even with the ignition off.

If it doesn't you need to verify there is 12 volts on the Red wire which is fusible link D.
If you have 12 volts there, either the fan motor is bad or the ground wire for the fan motor which is a Black wire is not making a good connection. That ground wire bolts to the frame cross member.

Also verify the wires on the bottom of the Main fan relay socket are not burnt.

 

I'm assuming you're troubleshooting the Main fan not coming on?
YES

The Main fan relay is the one mounted on the driverside fenderwell in front of the battery.
YES, I KNOW

The wires going to the relay socket are as follows.

Dark Blue has 12 volts when the ignition is in Run or Start.

Dark Green/White wire is grounded by the ECM to energize the relay. (Such as when you short A to B on the Diagnostic connector and turn the ignition On).

Red wire comes from fusible link D and has 12 volts at all times.
YES, I KNOW THAT BUT VISUALLY CANNOT BE SURE I AM LOOKING AT THE CORRECT LINK.

Black/Red wire goes to the fan motor. When the relay closes, 12 volts from the Red wire then goes to the Red/Black wire causing the fan to run.
THERE IS A SECTION OF WIRE LOOM NEXT TO THE RELAY AT THE FAN SHROUD THAT I WAS UNABLE TO SCREW WITH DUE TO EVERYTHING BEING HOT (TEMP) AT THE TIME...I WOULD ASSUME THAT THOSE WIRES RUN FROM THE FENDER MOUNTED RELAY AND FISH OUT OF THE LOOM AND GO TO THE MAIN FAN...CAN I PULL THE PLUG ON THE FENDER RELAY AND TAP IN 12VDC WHICH SHOULD THEN BE SENT TO THE MAIN FAN TO DETERMINE IF IT IS THE FAN OR SOMETHING ELSE?

If you remove the Relay from the socket, you can take a paper clip and short the Red wire to the Red/Black.
GEEZ, I SHOULD HAVE READ THIS A BIT FARTHER TO THIS POINT HOWEVER, I NEED TO DETERMINE IF 12VDC IS AT LEAST GETTING THROUGH THE COMPONENTS TO THE FAN IN ACTUAL USE.

The fan should run even with the ignition off.
SEE ABOVE BUT, WILL TRY TOMORROW ANYWAY.

If it doesn't you need to verify there is 12 volts on the Red wire which is fusible link D.
YEAH, OBVIOUSLY ONE SIDE CONNECTS TO A BATTERY SOURCE ON THE "LINE" SIDE BUT, WHERE DOES IT CONNECT TO ON THE "LOAD/DEVICE SIDE" AS THAT IS WHERE I WILL MEASURE FIRST TO BE SURE LINK IS NOT BLOWN.

If you have 12 volts there,
SEE ABOVE

either the fan motor is bad or the ground wire for the fan motor which is a Black wire is not making a good connection. That ground wire bolts to the frame cross member.
IT APPEARS TIGHT BUT, IS THE FRAME OF THE MOTOR GROUND OR IS EVERYTHING ISOLATED..IF IT IS GROUND, THEN I WILL RUN ANOTHER GROUND TO MOTOR CASING TO BE SURE.

Also verify the wires on the bottom of the Main fan relay socket are not burnt.
ALREADY DID THAT.

 

With all the posting and copying I may off missed it, but did you run a 12v wire straight to the fan motor to see if it runs full speed.

 

With all the posting and copying I may off missed it, but did you run a 12v wire straight to the fan motor to see if it runs full speed?

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***that is what i am trying to determine at this point...the car was too hot for me to screw around with but, AGAIN, what i want to do is feed 12vdc directly to the main fan motor to see if it is running correctly or at all......i was looking for a direct access point someplace to feed 12vdc to the motor as my first gig...

...next, if the motor ran, i then need to determine items listed in my previous posts.....i am trying NOT to have to pull the fan motor to feed it power directly and if it runs, have to determine bad internal relay contact, bad fusible link, etc.....please, re-read the post for your enlightenment.....hooked on vettes seems to have this issue well in had at present........thanks for the reply.

 

Remove the Fan relay from its socket.

Take a piece of wire and poke it into the prong of the relay socket where
the Black/Red wire is. Then touch the other end of the wire to the Positive
lead of the battery. The fan should run.

Just make sure you plug the jumper wire into the proper prong of the
relay socket.

 

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thanks for reply...will do this in morning AND POST RESULTS and to memorialize, BIN LADEN HAS BEEN KILLED!.....YIPPEE! - GOD BLESS AMERICA!

 

VERDICT......

....Main fan motor defective......

1)....split apart wire loom near fan and skinned back both wires to
it...

2)....ohmed ground wire to block (continuity) and was good...

3)....also ran a secondary ground as "it couldn't hurt"...

4)....tested voltage at other "hot" wire to fan and had power to
fan....

......SUMMARY; main fan motor bad!

"hooked on vettes", thanks for the help as it saved me a great deal of time and accelerated the troubleshooting process!

 

Now you know in the future where to start rather than random guessing. Always check what is NOT working first. Glad you found it.

 

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.....I was NEVER "random guessing", but was up against time constraints and his assistance to condense everything shortened the inevitable by measured amounts....