Hello all,

I am currently trying to charge my AC system and think there is another electrical problem related to my 3.0 to 4.0 motor swap.

The AC compressor is not getting a signal. The donor truck and my truck are the same years (1992), both manual transmission, and both ext cab. The biggest difference between the donor truck and my truck are;
donor truck: 4.0ohv, XLT, power everything; my truck: 3.0, no power windows, locks, or seats.

I have already noticed the front speakers do not work without a little re-wiring for this swap; that is why I suspect the wiring is different.

Does anyone have a fix for this?

 

Did the 1992 3.0l have AC?

Have to ask, lol

The AC compressor clutch is activated by the switch on the dash
This switch has its own fuse in the cab fuse panel
When AC ON is selected then 12volts is sent THRU the TWO Pressure switches on the AC lines, and then to the AC Clutch Cut Out Relay(WOT Relay), then to the AC clutch

Fuse-------------Cab switch------------pressure switch--------------pressure switch-----------------relay----------------compressor clutch


I would first see if Clutch is working, unplug its connector and apply 12v and Ground to the 2 connections, there is no polarity, its just a coil, it should click when powered

Then key on/AC on use a volt meter or test light on the Pressure switches, one wire should have 12v when you unplug the one switch

If you are not getting 12v then fuse could be blown.

WOT relay rarely fails, when this relay is OFF it passes power to the clutch, when activated it turns off AC clutch, so not likely to cause a problem but of course can, its a 5 pin relay

 

Thanks, RonD

That simply wire diagram was exactly what I needed. Once I jumped the pressure switch connector the compressor kicked on.
The connector had some blue gunk all over it though, so I changed both the connector and the switch. The new switch still didn't allow voltage through; so I jumped the connector to try and charge the system thinking once the system had some refrigerant the switch would work.

Now I have another issue; the system is not taking a charge from the lo-side to the hi-side even when the A/C clutch is engaged. Maybe I need a new dryer or orifice tuber but would either of these stop the hi-side from charging?

• The system held a vacuum for over an hour and the vacuum was run for another hour prior to me trying to charge the system. (Reading was roughly -30 before adding r134)
• Then I added r134 to the hose; purged any air in the r134 line and opened the lo-side. (Not sure what measurement to read, but the lo-side gauge needle jumped to the middle)
• The hi-side gauge did nothing.

A little back story:

• In October of 2018, I finished installing a rebuilt 4.0 along with all new A/C components, so I could run r134a clean-the system was previously run using r12.
• Since I was running on a newly rebuilt engine I hooked the A/C system up but left the power to the clutch unplugged.
• I did not have time to take your (RonD) advise to pressurize the system and worry about the system charge after the engine was broken in.
• I just started the new engine and broke it in without doing anything to the A/C system; that was close to 8 months ago.

Any advice would really be appreciated?