Figured it start a new thread because the 134a capacity thread evolved into electrical diagnostics.
I narrowed my ac compressor issues down the the computer/ Wide open throttle line.

I figured it's either the ECM is getting an errant signal or it's the ECMs fault.

Im wondering how the ECM gets the WOT signal is it from the TPS? Or vacuum pressure? I saw on the mustang forums something about that WOT throttle circuit being based not on throttle position but engine load based on vacuum pressure. Or maybe its both?

So I'm wondering are there easy diagnostics for the TPS or vac pressure sensor?

another possibility I was considering is could it be a bad ground on the ECM? And how to check for that? From the schematics if seen the positive part of the relay is a constant, as long as the AC line pressure sensors are ok. And the negative ground is supplied by the ECM. So ECM cuts ground at WOT, and that de energizes the relay.
grounds in my experience can exhibit the strangest symptoms. It doesn't always just stop working, as the ground can find other routes. And trigger other random things to be outa whack. Like headlights flashing with the flashers from a bad trailer ground. they wont work with headlights off. But then they actually ground through headlights when on.
the compressor kicks on with the engine off. And when I start the engine it runs for about 5 seconds while the RPMs stabilize, then cuts out. And wont come back on again till the engine shuts off. Maybe it's a long shot but maybe the ECM is lacking ground and the AC is grounded through other circuits that it's not supposed to until the engine is running and the ECM needs those? Because voltage does not drop to zero when compressor kicks off. The pink ECM switched wire when I connect test light to positive batt and probe wire its bright at first but then when engine gets going light just dims by half.

 

Tps sensor is good. Back probed and went gradually from closed throttle 0.9v to 4.66v WOT

 

Yes, its from TPS sensor only

WOT relay's coil gets 12v with key on, and it is grounded by computer pin 54 IF computer sees above 4.5volts from TPS
But if the wire from pin54 to WOT Relay has been shorted to ground then it would close relay with key on

So key on, test WOT Relay slot 85 and 86 for 12volts, one should be 12v with key on

Then test from that slot to the other slot and should see 0volts as that other slot is not a ground until computer grounds it
Or test from battery positive to "other slot" and should see 0volts, not a ground

If it is a ground then leave meter or test light connected and move around the wiring harness to see if there is a short to ground

If its not a ground then all should be OK with the activation of the WOT relay when at Full Throttle


But in your other post there was an issue with what I saw in the slot wiring
Slots 30 and 87A should activate the AC compressor clutch, not 30 and 87

 

maybe I have the older set-up. This is how I remember it. The middle was just an open hole (87a). When energized it connects top and bottom

 

Actually that drawing is backwards. When testing for positive and negative KOEO
12 o'clock pin was hot
9 o'clock pin also hot.
6 0clock negative
3 oclock negative

12 and 6 oclock go to the compressor and 9 oclock goes to the pressure switches, 3 oclock goes to the ECM.

So if I ground the wire going to the ECM it would work as intended just w/o WOT.

But I'd rather find out why the ECM thinks it's at WOT all the time. Or maybe there is some kinda connection issue. Either ECM power or ground, or the TPS or wire lead from ECM to AC relay. If all those are good than it's just a bad ECM.

 

No, 86(9 o'clock) would get 12volt with key on, but not from pressure switches, it comes from EEC relay

87 appears to be the 12v from the pressure switches, turn off AC switch in cab, key still on, and see if that 12volts goes away, it should

That would make 30 the OUT to compressor, and that would read as a Ground since compressor's clutch is grounded, and it just a coil of wire

85(3 o'clock) would be the ground from the PCM and should only be active at WOT

So with key on, when you insert the relay into its socket does it "click", activate, it shouldn't


And test the relay with OHM meter tabs 30 and 87A should show 0 ohms, so connected, and 30 to 87 high ohms, no connection