AC compressor not running

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21 Apr 2013 18:49 #14424 by ahspros
AC compressor not running was created by ahspros
I am new to the 928. I have 1986.5 with 67,000 on the clock. P.O. said AC had small leak and I needed to just add some Freon. This is a R12 system and I have a 20 lb. of R12 left over from other events. I tried to add some Freon with no luck. Compressor would not turn on nor would the fan on the condenser come on. All fuses are good and fan in dash will blow just fine. What am I overlooking?
It is starting to get warm here in North Carolina and will need some cooling in a few weeks.

Walt

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21 Apr 2013 20:12 #14425 by 928mac
Replied by 928mac on topic AC compressor not running
Well, just a bottle of R12 may not have enough pressure to add to the system.
That said, I would think that if it was low enough it would take some.

A R12 recharge station heats the R12 to increase the pressure
I found an old one and bought it.
You do not want to heat the bottle!, let me be very clear on that
Maybe someone will pipe up on how to short the compressor, I don't have a picture of the switch.
You know, you should check the fuses for the AC, that could be one reason it does not kick in.

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21 Apr 2013 20:46 #14426 by mm928
Replied by mm928 on topic AC compressor not running
Common problem, there are a few good A/C guys here that will pipe in...me? I had someone do it... :( Turned out the compressor was fine just needed a new belt. Has been running ever since with stock 83 parts otherwise.

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -

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21 Apr 2013 22:27 #14432 by wallyp
Replied by wallyp on topic AC compressor not running
Several possibilities for the problem.

A 928 owner is required by Federal and State law to own a 12-volt test light, so take your test light and check for power on the connector located on the single black wire that runs next to the oil dipstick. With the ignition switch on, ac switch pushed in, bottom lever on one of the middle positions, and the blower switch on, there should be power at the connector. There should be a loud click from the compressor clutch when you set the controls as above. If not, then put the bottom lever on DEFROST (all other switches on as above) and see if you get the click or if there is power at the connector.

The electric cooling fan on your car comes on only when the refrigerant is hot or the coolant is hot.

Go to the 928 Specialists website at www.928gt.com , go to the tips and links on the left, find Wally's World, find the HVAC paper there. It has a lot of info about how the HVAC system works on the 928. Lots of reading, but your life will be easier and cheaper if you read and understand the info.

Wally Plumley
928 Specialists
www.928gt.com

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22 Apr 2013 21:03 #14455 by mm928
Replied by mm928 on topic AC compressor not running
Wally is the man on this....and most other things as well....listen to him!

1983 928S - 16v 4.7L L-Jetronic
Dark Grey w/ Blue Leather
85/86 exhaust manifolds
Y-Pipe
SS Hi-perf Cat
S4 springs
Bilstein shocks
Air pump delete
VIN: WP0JB0926DS861180
- - Isn't Life great? - -

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24 Apr 2013 09:50 #14495 by ahspros
Replied by ahspros on topic AC compressor not running

Several possibilities for the problem.

A 928 owner is required by Federal and State law to own a 12-volt test light, so take your test light and check for power on the connector located on the single black wire that runs next to the oil dipstick. With the ignition switch on, ac switch pushed in, bottom lever on one of the middle positions, and the blower switch on, there should be power at the connector. There should be a loud click from the compressor clutch when you set the controls as above. If not, then put the bottom lever on DEFROST (all other switches on as above) and see if you get the click or if there is power at the connector.

The electric cooling fan on your car comes on only when the refrigerant is hot or the coolant is hot.

Go to the 928 Specialists website at www.928gt.com , go to the tips and links on the left, find Wally's World, find the HVAC paper there. It has a lot of info about how the HVAC system works on the 928. Lots of reading, but your life will be easier and cheaper if you read and understand the info.

Went to this site did not see the tips and links on the left.

Walt

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24 Apr 2013 16:44 #14499 by ahspros
Replied by ahspros on topic AC compressor not running
OK I think I found the antifreeze switch. Is this the relay with a capillary line and two wires? checked the leads and no power on either one with AC on full. Did have power on the low pressure lead. Will try putting power on the clutch connector located on the single black wire that runs next to the oil dipstick. Must be the small relay on the control board. Am I going in the right direction? Any comments?

Walt

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24 Apr 2013 22:10 #14504 by wallyp
Replied by wallyp on topic AC compressor not running
"Went to this site did not see the tips and links on the left."

They are there...
Go to: www.928gt.com
At the bottom of the home page, click on the appropriate entry for the browser that you use.
In the black block on the left, find +928 Tips/Links and click on the +.
Find +Wally's World (928 Tips) and click on the +.
Find The HVAC System and click on it.
Print the paper, and read it at your leisure.

On the '86, current flow to the compressor clutch is:
From the small relay in the HVAC head unit on a violet/yellow wire to the Evaporator Thermoswitch (freeze switch); from the freeze switch on a lilac/yellow wire to Terminal G21 (lowest terminal on the right side of Plug G); from there behind the Central Electric panel to Terminal T13 (3rd terminal up on the left side of Plug T); from T13 on a black wire to the Low Pressure Switch (on the Receiver/Dryer); from the Switch on a black wire to Terminal 9 of the 14-terminal connector; from Terminal 9 on a black wire to the compressor clutch; from the compressor clutch to a ground connection.

If you have no power on either side of the freeze switch (it is not a relay, but a thermal switch that opens at 32 deg F or lower, closes above that) with the AC and the blower on, the most likely problem is the small relay or a connector in the circuit. If you have no power at the freeze switch, you will have no power at the low pressure switch or the compressor. There is also a fan switch on the receiver/dryer - that is probably where you are seeing power.

Remember that voltage isn't power. It is possible to have 12+ volts on a meter, but not have sufficient power to operate the compressor clutch.

Wally Plumley
928 Specialists
www.928gt.com

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27 Apr 2013 14:32 #14528 by ahspros
Replied by ahspros on topic AC compressor not running
AC clutch still not pulling in. Did fine the site on Wally's world about the AC. Replaced the small relay with larger one with no problems. This is what I get:
1. 11.74 volts at the freeze switch with engine not running.
2. 13.72 volts with engine running.
3. Connect to wire going to low pressure switch volts drops to 0.24 volts at freeze switch with engine running.
4. Connect battery power to wire at freeze switch going to low pressure switch (with freeze switch disconnected from controller) clutch will pull in.
5. Have 11.94 volts at fuse for AC and engine not running have 13.72 volts with engine running.

Have decided to keep the AC and ditch the 928.

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27 Apr 2013 14:34 #14530 by ahspros
Replied by ahspros on topic AC compressor not running
Any 928 shops in Charlotte, NC that can digest my AC issue?

Walt

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27 Apr 2013 14:54 #14531 by 928mac
Replied by 928mac on topic AC compressor not running
If I understand your explanation of your problem

Ok it sounds like you may have a near broken wire or a highly corroded connection on that wire that goes to the low pressure switch.
Think of it like trying to start your car with a speaker wire from the battery.
You proved it by jumping to the switch with another power source.
Do you have a head lamp or signal light that you can use to check for power at the fuse,
(with two wires attached to the bulb) and then you will find where the power stops and where you still have it.
A test light will only show that you have some power but not draw enough current like a headlamp would, thats why I recommend you use a load large enough do draw some power.

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27 Apr 2013 17:06 #14533 by ahspros
Replied by ahspros on topic AC compressor not running
If I connect battery power through the freeze switch and through the low pressure switch and the clutch will pull in. Just will not pull in when connected to the controller, which has the new relay.

I have 13.78 volts (engine running) at the freeze switch but when I connect to the clutch voltage drops to 0.24 volts. I even ran a wire direct to the clutch bypassing the freeze and low pressure switches and had the same issue of the voltage drop.

The only way to get the clutch to pull in was to connect directly to the battery source.:mad::confused:

Walt

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27 Apr 2013 17:11 #14534 by ahspros
Replied by ahspros on topic AC compressor not running
I forgot to say that I have yet to test the power at the fuse with some kind of load. I will connect straight from the fuse to the clutch for a load test. Will keep fuse in line for protection.

Walt

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28 Apr 2013 09:05 #14550 by wallyp
Replied by wallyp on topic AC compressor not running
"Remember that voltage isn't power. It is possible to have 12+ volts on a meter, but not have sufficient power to operate the compressor clutch."

Voltage is pressure, Amperage is flow.

Try to visualize having a wire from the fuse to the freeze switch that is broken except for one tiny strand. That would give exactly the symptoms that you are having.

As Brad pointed out, a poor connection or near-broken wire somewhere between the fuse input and the freeze switch can cause this. The undersized relay that you replaced is by far the most common cause. Check the plugs on the command unit, etc.

You just have to find where you are losing the Amperage, not the Voltage.

Wally Plumley
928 Specialists
www.928gt.com

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28 Apr 2013 09:31 #14551 by smtcapecod
Replied by smtcapecod on topic AC compressor not running
A factoid that may or may not be related to your 'small leak- but not the compressor issue.

I'm finding, anectdotally, that the routing of the hard aluminum A/C line is subject to abrasion on 86.5- probably in conjunction with sagging motor mounts. In the attached photo, there is an abrasion mark forward of the passenger side strut tower. On a couple of local cars, the timing guard has rubbed against and chafed through the aluminum A/C line. Fingers crossed that your small leak is less substantial!

Attached files [img]media/attachments/14918=1799-engine compartment pass side.jpg[/img]

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