AC Tribulations

driller

El Presidente
Staff member
Paid Member
Rigged up the SCT X4 and laptop to the car and ran some logs for diagnostics on the AC.

First test, look at AC Clutch PID and AC Pressure PID. Zero results on AC Clutch and very low AC Pressure PID when Max AC engaged. Second test following the diagnostic flow chart using a jumper wire at the AC Cycling switch showed same results. Voltage was verified at AC Cycle switch from EATC whenever AC was commanded, so the conclusion is there is no link to the PCM (and VCRM) over the SCP datalink. :cautious:

As a third and final test, I put together a temporary harness to go between the AC Cycling switch circuit and the AC Clutch, effectively bypassing the PCM and VCRM. Started car and turned on AC Max. AC Clutch engaged and system indeed worked, likely not at optimum with unknown refrigerant charge but the AC lines and blower output were cold none the less.

I believe the route I will go from here is to use a trinary safety switch to energize the AC Clutch via a relay. I can use the EATC circuit from the Cycling Switch to run through the trinary switch to the AC Clutch. Since the fan appears to function as it should (I was also able to datalog the variable speed fan PID) I think I will be fine without a fan controller. But if later down the road, the fan circuit starts acting up, I can add a fan controller and relay triggered via the trinary switch. Since I don't necessarily feel comfortable with the AC Cycle switch circuit carrying the load for the AC Clutch, I believe it would be best to utilize a relay to energize the AC Clutch coil. According to the PCEDM, the AC Clutch coil draws 2.5 to 4.5 amps. I'm not sure the EATC is designed to carry that load.

Here is a typical wiring schematic for the trinary switch:
11076-VUS-2.jpg
I will use the EATC circuit from the cycling switch to feed the circuit to the trinary switch and then to the relay I will add for the AC Clutch. The trinary switch will open the circuit, disengaging the AC Clutch when high or low pressure cutoffs are reached to protect the AC system components.
trinary.jpg
Once I acquire the needed parts I will wire it all up and then return to the shop to have the AC system charged. :cool:
 
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driller

El Presidente
Staff member
Paid Member
So we got all the parts for the wiring project while I was at Carlisle and I just completed wiring in the trinary safety switch and relay for the AC clutch.

It works! (y)

Sort of...

At first I was dismayed when I hit the Max AC button and the compressor did not kick in. I checked for obvious faults and for proper grounds and voltage where they should be and the only alternative was an open safety switch. Since I had wired in 2 pin connectors for the clutch circuit and the fan circuit on the safety switch, I disconnected the clutch circuit and rigged a jumper using a mating connector. The compressor then started cycling. :)

My guess is the system pressure is below the safety switch setting but I can't really say as I do not have a set of gauges. We are setup with an appointment at the shop tomorrow to charge the system and we will see if the trinary switch allows the AC clutch to function with proper system pressure. But as it is, it certainly looks promising since the cycling switch is doing what it is supposed to do.

Basically, the trinary safety switch replaces the pressure transducer on the high side of the AC system. The safety switch has a low set point and a high set point for the refrigerant pressure. The system pressure must be above the low set point and below the high set point to function. Here is a crude wiring diagram for what I have...

Trinary.jpg
I'm not utilizing the fan control circuit from either the trinary switch or the aftermarket fan controller since oddly enough the cooling fan functions just fine through the VCRM. I do have the Dakota Digital PAC 2700 Fan Controller and a Painless Performance 70A fan relay should the need arise in the future.
 

tixer

Lincoln Evangelist
Staff member
Paid Member
I should print this and save it in the factory service manual. [Aircond_Addendum-LOD-2022]

Here's to hoping it all works beautifully after a charge!
 

driller

El Presidente
Staff member
Paid Member
It works! :love:

Not without a slight alteration however. :sneaky:

No info was supplied with the trinary switch, so I was left to Google my way through the wiring. Most hits seemed to point to the black pair of wires being the fan circuit and the other color being the clutch circuit. One very specific diagram showed the same colors as the switch I had which showed the Black and Black/Yellow pair as the fan circuit and the Brown and Brown/Black pair as the clutch circuit. Turns out that was wrong, the color scheme was exactly opposite and I credit the shop tech who was helping to diagnose the wiring.

We even went so far as to disable the cooling fan to be certain the AC clutch would kick out at the high set point. Turns out the high set point was approximately 425 psi and the fan circuit set point was around 170 psi. We did not find the low set point as we would have had to evacuate the system and we chose not to do that.

For the record, the trinary switch used was the Four Seasons brand # 36581. After removal of the OEM pressure transducer, it threaded right onto the high pressure side manifold piping up next to the AC condenser. The O-ring seal and integral schrader valve allows removal and replacement without loss of refrigerant.

I will backtrack and correct my wiring diagram to indicate the correct wire color scheme when I have more time. At least that way should anyone refer to this in the future, they will have the correct information. ;)

:cool::cool::cool:(now)
 

tixer

Lincoln Evangelist
Staff member
Paid Member
Fantastic news!!!

Cool and comfortable, in a car that was already cool. what an adventure.
 
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