jss06c6

Gents,

Left Saturday morning for coffee and cars and air conditioner would not cool. Ran pefectly last time I drove it (two weeks ago). Compressor not kicking on. Freon charge sitting just over 65 pounds (static pressure w/o system running). Fuses are fine. Any thoughts from the experts on troubleshooting?

Thanks!

zr-1 guy

sounds like you may need a new compressor

Dynomite

Check your AC cycling switch. Disconnect the AC Cycling Switch connector and with engine running and AC on see if you have 12 volts to one side of the connector. Then measure the resistance between the two pins of the AC Cycling Switch. If there is NO resistance and you have 12 volts to one side of the connector your compressor clutch should engage.

If you do not have zero resistance between the two pins of the AC Cycling Switch you either have not enough Freon in your system or a bad AC cycling switch. I am thinking with 65 psi on the low side with engine off the AC Cycling Switch should be on (Connectors/points closed or zero resistance between Connectors/points).

I am just guessing but am thinking the cycling switch should turn off at 25 PSI (compressor clutch disengaged), and back on at 40 PSI (compressor clutch engaged) low side pressure. I am thinking greater than 400 psi on the high side will turn off the compressor (disengage compressor clutch). See AC Normal Low and High Side Pressures TIPS

In your case you may not have 12 volts at the AC Cycling Switch connector or an AC cycling switch that does not close.

Or a bad compressor clutch as zr-1 guy suggests.

I am interested and learning here on AC systems so will stand by for the experts to give us the details on AC diagnostics (I will modify this post as I find new information). I just today replaced an AC compressor on my 1986 Silverado and added a new Accumulator/drier. Will have the system evacuated tomorrow. I had a line break on my 1991 ZR-1 at the Accumulator/drier and replaced Accumulator/drier followed by an evacuation.

It is my understanding that moisture gets trapped in the oil (compressor lubrication) and you have to pull a significant vacuum to rid the oil of moisture. It is also my understanding that the Accumulator/drier should always be replaced if you open up the AC system to atmospheric pressure.

Make sure one Female Contact of the AC Cycling Switch Connector has 12 volts with Key On and Air On.
The AC Cycling Switch on the Low Pressure Side of the AC System is shown in the background in this photo. With engine running, the shorting across the connector should engage the AC clutch if the AC compressor is functional.

jss06c6

Thanks guys. Sure hope it's not the compressor since it has been working perfectly up until now. No signs of any leaks at all (usually have some AC oil residue around leaks) all lines and connectors are dry and clean. I pulled the connector off of the cycling switch to check for corrosion, none present. Will put a meter on it and see what the resistance is on the switch and check for 12V as well.

Pulled the specs on the AC HI/LO cycles.. 25 psi low side will kick on compressor and kick off when pressure reaches 436 psi on high side (page 8A - 67-7 in 1991 electrical service manual supplement).

Will continue to troubleshoot. Thanks for the help.

Dynomite

Thanks for the information.........and let us know what the issue turned out to be
I am thinking there is a kick off and kick on pressure on the low side cycling switch but do not know exactly what those numbers are.

jss06c6

When you say hotwire.. What are you doing exactly? Are you shorting across the switch?

Thanks!

Dynomite

Shorting across the connector.......use a paperclip and stick each end in alongside one of the female contacts of the AC Cycling Switch Connector. Make sure one Female Conact of the AC Cycling Switch Connector has 12 volts with Key On and Air On.
With engine running, the shorting across the connector should engage the AC clutch if the AC compressor is functional.

The AC Cycling Switch on the Low Pressure Side of the AC System is shown in the background in this photo.

jss06c6

Perfect! Thanks. Will check tonight when I get home.

gbrtng

Do you have a flashing LED on the control head? If so, pull the error code(s) ...

jss06c6

Didn't at first. Noticed yesterday that the LED flashes continuously. Pull code from OBD1 port below dash, yes?

ghlkal

To enter diagnostic mode, push and hold the fan up arrow and down arrow at the same time until the LCD shows -00
You are now in diagnostic mode
(Don't read these from the OBD 1 port)

09 = Low Freon Detected (which is the only one I remember)

wro87

Don't want to hijack but the same thing has happen on the 92Z of my sons at first the clutch would kick in but wont now. I jumpered the low pressure switch along the inner fender and it would not kick on took AC pressure reading but it was sitting around 45# with the compressor not running I have checked all the fuses and they seem fine. Could it be a relay and were might it be?

Thnak gang wro87

ghlkal

This may or may not help ...

Once the "low Freon" code is set, the compressor will NOT engage again until the faults are cleared. I've tried pulling a fuse, but the only way I could reset my HVAC controller was by disconnecting the battery for a few minutes. Once the codes are cleared, the compressor will engage again.

So, if the system was low, just charging it doesn't get the compressor running again -- you have to clear the code.

jss06c6

Checked ECM diagnostic code from OBDI connector, no faults, sends code 12 which is all good on ECM side. Did not read how to read the codes on the control head. Will check that. It does flash for a while, then stops and shows steady LED. I'll disconnect the battery to reset everything and see if there are any changes.

Dom, don't have 12 volts at switch. Switch is closed (0 ohm). Next upstream is the relay. Pain in the butt to get to (left of steering column on inside of firewall). Will have to pull the panel off under the steering column.

Will keep working back and find the issue.. I guess 23 years will have some random electronic issues,,,, even with only 38,233 miles on the vehicle!

jss06c6

Just checked.. fault code 09 (low freon). Disconnected negative terminal on battery & waited 5 minutes before reconnecting. Rechecked fault codes, none detected. Started engine, engaged AC (auto), compressor kicked on, then off, then on, then off.. turned off AC. Certainly low on freon. Cycled on/off every 2 - 3 seconds.. THANKS! Glad I don't have to get to the relay.

Found the cap on the low side was missing o-ring. When I removed it there was some evidence of leakage. Replacing it without the o-ring allowed the cap to slightly depress the schrader valve and leak. Must have had enough seal when all the way down to limit the leakage. Replaced the O-ring with refrigerant grade replacement. No leak and good seal. Now I've got to find R-12!! Sure used to be easy to work on auto ac when I could get R-12.

Codes for those needing them below (thanks to WILDRIDE)..

You press the up and down fan controls at the same time and hold them for ~5 seconds. This will display 00 on the readout. You then press the up or down fan control to cycle through the different choices. Pick one and press the center fan control to display the information.

First the HVAC Diagnostic codes

0 System Faults
(one of these will be set if your air conditioning controls have an LED flashing)
00=No Faults
01= Temp Door Motor Circuit Fault
02= Temp Door Motor Circuit Fault
03 = Ambient Sensor Open
04 = Ambient Sensor Short
05 = In-Vehicle Temp Sensor Open
06 = In-Vehicle Temp Sensor Short
07 = Solar Load Sensor Open
08 = Solar Load Sensor Short
09 = Low Freon Detected
10 = UART Failure


Other Parameters available:

1- Temp Setting 60F to 90F

2- In-Car Temp Sensor 10 = HOT -130 = 230 = COLD

3- Outside Temp Sensor 10 = HOT -130 = 230 = COLD

4- Sun Load Sensor Max light Max Dark
L98 38 183
LT5 115 -110 = 210

5- Ignition System Voltage 0 = 9 Volts -155 = 255 = 16 V

6- Engine Speed (RPM divided by 25)

7- Vehicle Speed

9- A/C System Mode
00 = OFF
01 = Re-Circulation
02 = A/C
03 = Bi-Level
04 = Heater
06 = Defrost
07 = Vent
10 = Manual Re-Circulation

10- Blower PWM 0 = 0 Volts 128 = 14 Volts

11- Program Number 00 = COLD -155 = 255 = HOT

12- Mix Number -155 = 255 = COLD 00 = COLD

16- Coolant Temperature In degrees C

17- Solar Correction 114 = Max light 128 = max dark

30- Stored Full Hot Value 0 to 50

31- Temp Door Travel Range 100 to 200

34- Temp Door Position Requested 00=Full HOT -153=253=Full COLD

35- Compressor On Time 0.1 second increments

36- Number Of Times Below Critical Time

37- Software Version Number

Dynomite

Ebay......but you have to sign that you are qualified/licensed to use R-12 or will otherwise give your can of R-12 to someone qualified/licensed to install R-12.

Excellent Information...thanks
And thank you Gary........See HVAC Display as Digital Readout TIPS

jss06c6

Well.... should have done this earlier but I got the freon and hooked up my gauges. Shorted the hi/lo pressure switch and fired up the engine. Set ac to max cool and checked gauges. AC compressor clutch engaged full time..... no compression! High side reads same as lowside! About 75 psi. With system running perfectly two weeks before it quit, I'm puzzled now. Hard to believe I've had a catostrophic failure in the compressor. Never seen that in all the vehicles I've owned.. will continue to dig through diagnostics to see if I can diagnose the problem..

jss06c6

Was low on Freon after all. Compressor is fine, thankfully...

combatdoc

FYI my AC stopped working with flashing light, turns out in the back of the manual there are directions for re-setting the system, pull two fuses for a period of time put them back in a "BANG" it works.

jss06c6

Thanks.. I disconnected ground on battery for 30 seconds and had same success...