legacycentral bbs

Bad solder joints on climate control box. Pull and redid soldering.
Something like that on evaporator temperature switch. Bypassed it with a jumper cord.
So far so good.

Bad pressure switch isn't very likely. That switch doesn't cycle unless there's abnormal conditions.
Check line pressure first. If you're not seeing at least the 50 psi on a warm day, the refrigerant is lost.
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After replacing the compressor and expansion valve, the car won't activate compressor anymore.

I double checked that everything I unplugged (evaporator temperature sensor, pressure sensor at filter drier) got plugged back in.

System was recharged and I know there's adequate pressure as when I hook up gauges, i see it.

When I jump the compressor manually (with harness detached), it activates so the clutch is good.

What's the pin-out and test procedure on the drier-bottle sensor assembly? There are four pins.

What else determines compressor activation signal?

Did the system have a vacuum pulled on it for at least 30 minutes prior to recharging?

This diagram may help.
http://www.main.experiencetherave.com/s ... ngdiag.jpg

The pressure switch on the drier is a trinary switch.

Pages 38-39 of the 90 Legacy wiring diagrams have the more detailed diagram
http://www.main.experiencetherave.com/s ... agrams.zip

vacuumed for a few hours.
Where is the evaporator thermo switch? There is a thermistor probe that shoves into the evaporator fins, but it is not a switch. I only recall one electrical component going into the evaporator and its just that one.

If AC kicked on fine before, but not now, what gives? I must have messed something up on something electrical.

The pressure sensor... do you know which one is low pressure and which one is high pressure cut out?

The low & high pressure switch is all in the same unit.

If I had to guess I'd say pins 3 & 4 of the B3 connector are the low pressure switch, while pins 1 & 2 are the high pressure.

Legacy777 wrote:The low & high pressure switch is all in the same unit.

If I had to guess I'd say pins 3 & 4 of the B3 connector are the low pressure switch, while pins 1 & 2 are the high pressure.

I can't figure out which pins are which, because the colors don't match period or how to read the connectors.

On the sensor side harness:
I have
4^1
3_2

1 Black-white striped
2 Blue white striped
3 red blue striped
4 Red white striped

Josh can you test the continuity between Blue/white and blue/red?
Black & red is the low-pressure cut out. It is open with no pressure present and at about 50 psi, it closes.

So, the other pair must be high pressure, which on mine is open. I don't know if that's supposed to be open or closed under normal conditions. Mine is open.

I'll try and remember to test mine. Shoot me an email to remind me.

I would say that the low pressure switch is supposed to closed under normal pressure. The high pressure switch will normally be open. When pressure raises too high, it will kick the fans into a higher speed to help draw the pressure in the condenser down.

You're dead on. The factory diagram did not explain it well enough so it was confusing.

Here's the update, the numbering likely doesn't correspond to factory allocation however, per:
On the sensor side harness:
I have
4^1
3_2

1 Black-white striped
2 Blue white striped
3 red blue striped
4 Red white striped

PER my diagram, blk/wht & red/wht is low pressure drop out switch. This disables the A/C system if the refrigerant pressure on high side drops below some point. It is OPEN with no pressure. It is CLOSED. This switch should not go open unless there is loss of refrigerant.

blue/wht and blue/red is usually open. When closed due to high refrigerant pressure, it activates the fan. I believe this is part of the normal cycle. This is not a high pressure cut out. There is a spring loaded relief valve at the back of the compressor that will vent refrigerant to prevent system component rupture in the event of a dangerous level of overpressure.


NOW....
going back to my system...
The system enabled compressor just fine before I replaced the compressor....

I pulled the evaporator, replaced the expansion valve. The evaporator has a thermistor sensor that goes to a 3-pin module that says 12v 0°C. I suspect this module is the thermostatic switch. This needs to be tested still.

I pulled and replaced the compressor. Man this was a PITA to remove. I think compressor overheat cut out is on the compressor side of the connector. I will have to check this.

"ac jumper pin" i don't know where this is.

I also replaced the starter. It's possible I jousted some wiring.


Ruled out:
pressure switch verified functional. Jumping low-pressure cut out does not turn on compressor.
Compressor clutch: activates fine when 12v applied externally.

Ok, thanks for the additional explantion. That will help someone in the future!

The AC jumper pin, is this the same thing as the AC short connector? If so, this is related to the fans and causes both fans to turn on at the same time vs. only the fan on the driver's side turning on with the radiator and the fan on the passenger side turning on with the AC.

If the compressor engaged before you did any work, I'd lean towards the wiring. Have you checked to see if you're getting anything at the AC relays. I'd suggest tracing it back to verify whether all the wiring is good and whether you're not getting an engagement signal from the mode controller or if the signal is getting broke somewhere along the chain.

Mode controller is the box that has all the HVAC buttons right?

I figured it out!
It's the goddamn HVAC control box.
The magnetic clutch is wired in series with A/C cut relay which is controlled by MFPI and requires the engine to be running.
I shorted the relay contacts at the socket and compressor engaged.

I jumped the brown wire at the evaporator switch to ground and it worked.
This tells me that mode switch is not engaging.

Turns out if I "punch" in the button at the control box, it would engage. If it doesn't, I have to bang on the dash above the box... so yeah, the mode control switch is not engaging.

Yup, mode controller is the HVAC control box with the buttons.

Looks like you found my other thread about the HVAC buttons not working. More than likely there are some bad solder joints. You can try taking it out, looking for the bad solder joints and resoldering them. That'll probably fix the issue. Or try and find a new HVAC control box.