Hi, i have a little problem with my Expedition. I bought it with non working AC, so i went to a shop to do a recharge. They recharged it, no leaks, but A/C clutch is not engaging. He checked the relay, it was OK, when directly connected + to AC clutch, it worked (Clutch engaged and it was freezing inside car).
Then I have left the place and at home, i have checked output form EATC which should lead to first and then to the second pressure switch. It worked, when i set the EATC the way it should start AC, i had +12 on pin 11 which should lead to swiches. Switches are also ok, and then it should lead to PCM (pin 41).
Does anyone have a pin-out of the PCM module please? I have just wiring diagram called "Automatic AC circuit", and there it just leads to PCM. And the part with a power for AC Clutch- there is Relay and the rest leading to AC clutch. But i cant find any wiring diagram to check the lead to the relay from PCM or where it goes from Can anyone help me with that? Why am I not getting a signal to engage AC clutch relay. Thank You

 

Is there please any expert for electronics with advise? PLEASE I still have just 0V on WOT relay

 

Is your 0V at the WOT relay on the activation terminal or on the "power through to the clutch" terminal.
Sorry if this description sounds odd but I couldn't think of another way to explain it.


On my ranger the WOT relay was not working so I just bypassed it. The A/C compressor doesn't turn off in WOT situations but the A/C works normal otherwise.

 

Have you tried visiting your local library? Most have a subscription to either AllData or Chilton TotalAccess. It's been awhile since i looked at the EATC diagram, but all 97-02 F150/Expeditions are wired the same. Only difference is the rear heat & a/c being tee'd into the front systems.

What terminal of the WOT relay are you not seeing the proper reading on? IIRC, the PCM pulls the ground signal on WOT to disconnect the compressor clutch, and supplies a ground signal at all other times.

Long story short, pull the relay and put a jumper wire between terminal 30 & 87 in its socket, then test again. If it works corrctly, replace the relay. If not, trace the wiring on pin 30.

 

That means, you also dont use the signal through high and lo pressure switches, if i get that right? So if there is something wrong in the system, your compressor could be easily damaged? I hope i will not be forced to also bypass the WOT relay.

 

Relay is OK, when i put it for example instead of fog lamp relay, it works OK, also when i put any other relay to the position of WOT, compressor does not engage. When i put the jumper the way, as if the relay would be "closed", compressor clutch normally engage. I dont know the pin numbers you mentioned, could you please put here some picture? When i use a "standard relay therminology", when i put a jumper between 87 and 30, clutch engages. When i measure pin 87 to the Gnd, i see +12V. When i measure pin 86 to Gnd i get 0V, when i measure 85, it is also 0V.

 

Bypassing the WOT relay only affects that function it does not bypass any pressure switches, it runs the same as if you never use WOT.

 

I use the standard Bosch-type relay terminal nomenclature. Pull one and look on the bottom, you will see the numbers. 30 is the oddball of the bunch.

Let me get this straight so I understand properly. Swapping the WOT relay into the fog light socket, fog lights work. Relay is proven good

Swapping a different relay into the WOT socket, compressor won't engage. Relay is not the problem.

Jumpering 30 & 87 on the WOT relay socket engages the compressor. Wiring on 30 & 87 is proven good.

You have a problem on the relay coil, Pin 85 or 86. The coil needs both a positive and negative to activate the relay and engage the compressor. Trace both for continuity to their targets. One will be the PCM, the other is switched 12v+

 

PERFECT. You understand it correctly. I have checked the line from WOT relay coil, which leads to PCM and it seems to be OK. The other contact, i am unable to trace, as I dont have the exact diagram. Do I understand it correctly, that this pin should lead to a fuse number 5 somehow (inside a cabin), so i should measure +12V there? How can i check, that the PCM works correctly and that it is trying to either send +12 or connect to gnd, depending on the function? (dont know which case is correct, as i couldnt find it anywhere) Thank You.

 

Generally speaking, most ECUs/PCMs output a ground signal, so fused switched 12v comes from the fuse box. There are a few exceptions to the ground signal rule such as on a Neon S Hetty Ricer Turd4, but they are rare.

Simple ties is to hook the meter to 85 & 86, set to voltage, then read it as follows:

key off
key on
key on, pedal at WOT

The meter should behave different at WOT than the other states. Since WOT cuts the compressor signal, I suspect the PCM will yank the ground signal at WOT