AC Clutch Won't Engage

[walt]

Just completed the Kuehl upgrade and charged the system without a problem, clutch engaged as it should and blew nice cool air out the vents. Things went south when I took it for its first ride, after 10 minutes the compressor cut-off for some time before coming back on. This happened several more times and now its not functioning at all.

In checking the AC relay I have power to pin 30 at all times however, pin 85 should have power with the ignition on and it does not. Fuse 20 was removed cleaned and replaced. Any thoughts where the fault may be. This is an 82 SC.

[RedCoupe]

The low pressure switch could have interrupted the electrical circuit to the compressor if you have somehow lost your refrigerant charge.

[Discseven]

Walt... relay in smugglers box gets stuck sometimes. Taping it some can quickly solve no-AC issue.

[86 911 Targa]

Compressor wire connections?

[Discseven]

Originally Posted by 86 911 Targa

Compressor wire connections?

Could be. I recall an issue like this with my '80. Connection at compressor was good. Think there was something with control switch where green and green and white stripe wires are. Too long ago to remember now. Need to check that when AC is turned on, power is feeding to compressor from switch. Also had that stuck relay problem once. (TY RoNo.) Also drop in pressure that set off pressure switch. And black death. (What's next!)

If you bought system from Charlie, you have product support for LIFE. Great guy.

Just noticed your orig owner. Impressive!

[T77911S]

did you check pin 86 for power

[kuehl]

Walt,

Feel free to call or email us if you can't resolve the issue.

[walt]

No power at pin 86 either with ignition on and off, power only to 30. Low pressure switch closed as it should be.

Thanks Charles, if I don't get this resolved in the next day or two I will call. All your equipment installed perfectly I just have an electrical problem lurking somewhere else.

Walt

[kuehl]

Walt,

If you have not wandered over this Thread regarding electrical issues it might be interesting to read. I can't say at this juncture if you are experiencing the same issue, but interesting reading.

On your problem, start at the one end and work your way forward. Such as:
1) Using an ohm meter, check for continuity between the 2 wires of the pressure switch.
2) Are you getting power back to the pressure switch, etc.

Griff

[T77911S]

I would not go over there, its going down the wrong road.

fuse 11 feeds pin85 of the ac rly
gnd is thru the starter solenoid.
if your evap fan still runs then this rly is not the issue.
if the evap fan is NOT running this is where to start.
this rly provides power to everything for AC

power for the clutch comes from the fan sw thru the temp sw.
check for power at the temp sw, both sides.

[kuehl]

I'll take a break and work on my car,
too many cooks in the kitchen, lol

[walt]

I have only 8.2 volts at the clutch, when I hooked up an external 12V it engaged instantly. So maybe when I had the engine out this past fall I pinched this wire. It looks to be connected directly to the temp switch. Does anyone know approximately how it is routed thru the engine compartment, I can follow it only a short ways until it disappears behind the engine. Or, is a faulty temp switch more likely.
Thanks.

[kuehl]

If you have a Kuehl 507 compressor: With a .015" nominal air gap (the space between the pulley face and the outer clutch hub) the compressor clutch will pull in completely with 5 volts.

If your system has a pressure switch, check for power on both sides of the switch.

[walt]

It's a Sanden SE-507 compressor about 12 years old but I'll bet it doesn't have 5 hours of actual run time on it.

Checked both sides of the pressure switch, reading 8.5 volts either way.

But this seems odd to me - with the ignition and AC controls on, when I disconnected the compressor wire the front condenser fan came on. Went back off on reconnecting.

[T77911S]

is the 8.2v with the wire connected to the clutch or not?

pwr comes from the AC fan sw and goes to the temp sw. from there it goes thru several connectors. at one of them it splits off and goes to the coil of the fan rly.

with the low voltage, probably due to a bad connection, the rly is not pulling in because the voltage is loaded down by the clutch. removing the wire allows for enough current to pull in the rly.

I would check both sides of the temp sw first. I would also use a test light,. a TL is a load and will show a bad connection better than a MM.
if pwr is good there then one of the connectors has a bad connection.

the clutch needs a lot of current to pull in. with a bad connection that adds resistance which reduces current.

[kuehl]

Walt,

In terms of component power load, or amps, on the AC circuit, assuming 12 volts:
Evaporator Blower Motor 13 amps
Front Condenser Blower Motor 2 amps
Comp Clutch 4 amps
So there is about 19 amps nominal (this is running amps excluding a higher start up load with the motor for a few seconds).
What is missing is the wire runs through out the system which will consume of volts or choke the amps along the way.


If you measure the voltage of the power to the compressor clutch at the factory male spade connector in the plastic sheath back the oil filter, on a system with clean connections and fully charge battery chances are you may not see 12v+ because of the voltage drop related to the long run of wire from the Thermostat. When things get old an corroded you can have a greater voltage drop as well a power drop related to the condition of the contacts in the thermostat, the fan speed switch, the connector at the primary AC relay in the Smugglers box, the contacts for the primary AC fuse (blue 25 amp fuse in position 2 nearest the windshield).

Below is the typical electrical circuit for a factory ac 2 condenser SC.

To take the AC compressor clutch out of the question measure the resistance of the compressor clutch coil (checking with an ohm meter between the compressor clutch wire and the body of the compressor), typically the Sanden will be 3-4 ohms nominal.
I doubt the AC pressure switch is putting any load on the circuit however you can check the resistance between it's 2 wires. I do recall one client whom had an issue with a clutch no engaging consistently, this was because they had their AC brackets powder coated; they removed the finish in a few areas where the bolts secure the brackets to eliminated the issue.

If you want to jump ahead to other common areas that cause voltage drops or reduce amp capacity you can start with these:
1) Insure the contacts for the primary AC fuse are clean, rotate the fuse a few times, check the condition of the wires that go into the fuse receptacle.
2) The female terminal spades in the connector for the primary AC relay in the Smugglers box, and the relay; we prefer a 20 amp min relay
3) If you have an original AC blower motor switch, they do carry a high load so the contacts wear or break down over time.
4) Contacts in the AC thermostat, a pita to inspect cause you have to take the thermostat apart, however you at least check the resistance between the spade terminals when the thermostat is set to max cold (green and green/white wires off the terminals).
5) The front condenser relays can get hammered because there was not fuse between the relay and the front condenser motor, I recall pins for the relay may be silver plated so corrosion is not as bad as zinc plated terminals, but you could remove the relay and put it back in or swap it out with another of the same type.
6) The front condenser blower motors will fail because of location and age. Good idea to splice in a 7.5 to 10 amp fuse in the hot wire at the harness at the blower motor.


Here is a typical SC AC schematic

[T77911S]

yes, the clutch can very well load down the circuit dropping the voltage, one reason I asked if he checked power with it connected. there will also be a voltage drop across the clutch coil to ground. but if it is loading it down it will probably pull too much current and blow the fuse.
I have had 2 jeeps that the comp clutch caused issues with how it ran. another story.

not much current on the cond fan compared to the evap fan. also cond fan on separate rly.

the sw can also drop current.

wiring is getting old and can increase resistance. I would bet a connection though.
if he added a pressure sw to the low side it could even be his crimps, if there are any.

I would go back to either the temp sw with a test light or to pin 86 of the cond fan rly,

[kuehl]

Walt,

If you feel ambitious you could use a meter that has amp measuring ability built in, say at least 15 amps, or get an inexpensive analog amp meter (EBay - cough) and start measuring the loads in the circuit, for example front condenser blower motor or what ever end you want to work on, typically you'd start at the compressor and work your way forward in the circuits

[rokemester]

Does anyone know how to remove the electrical connection on the Nippondenso compressor? It’s really locked in there!!

[kuehl]

what are you trying to do, objective?