AC & OD wiring help needed

[ofelas]

Hi all,

91.5 W250, need some AC & OD wiring pointers

1/ Where do I wire an additional momentary switch (second-gen shift lever) to act in series with the factory dash mounted OD switch? This is the red-headed stepchild 91.5 with the OD control module behind the glovebox, and the truck doesn't have the normally used OR/WH wire on the factory OD switch.

2/ Looking at the schematics - there seems to be no AC relay and ECM pin used for the compressor clutch cycling, unless I'm missing something.

Relevant FSM wiring diagrams attached; thx in advance.

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[cerberusiam]

IIRC, YL\BK and YL\DB will be the wires you tap the 2 wires from the stalk into. That should activate the control module.

The compressor is not controlled by the SBEC on this one, it is a control on the return AC line to cycle the clutch off when it gets too cold. Are you trying to bypass the control for the AC?

 

[ofelas]

BIngo, that did it on the second gen OD lever.

Alrighty. I did the following -

New gaskets & o-rings everywhere.

5oz oil in the compressor, 2oz in condenser, 1oz in evaporator & 1oz in drier.

Nitrogen in the system at 300psi and it held for almost 2 hours - no drop in pressure at all.

Ran 26psi vacuum on the system and it held for 2 hours.

Sucked in 40oz of R12 with the compressor cycling at 1300rpm + Max AC + blower fan on high.

Compressor OFF: 50psi low side and 220psi high side
Compressor ON: 25psi low side and climbs in a few minutes to 450psi high side.
Faceplate vent temperatures - 46-50 F

Raising the rpm to 1200-1300 turns the compressor OFF and high side drops almost instantly to 200-250psi

Why am I getting such high side readings, and is it normal for the compressor to be ON constantly until it de-clutches at 1200rpm?

 

[ofelas]

Got mine finally fixed.

My damn fish scales were bad; there was a low charge in the system.

Vacuumed the R12 out, refilled 38oz R12 on a digital stand scale.

Vents are blowing 36F air with ambient of 87F and 88% humidity.

Pressures are 36psi low and 195 high.

Compressor cycles 4 times a minute for 10-12 seconds a time.

New clutch went in anyway...holds a dollar bill against the front grill even while the fan is freewheeling at idle. Old clutch didn't do that.