AC only works if hot wired

[pjtoledo]

2005 reg cab, 2.3 with regular t-stat/no wires to t-stat, 5spd. manual AC.
301,600 miles, no previous AC work.

outside temp is 70-72 this AM during testing.
turn AC on, clutch does not engage, electric radiator fan does start.

static pressure 78-80 both low and hi side, 70-72 degrees outside.
both low and hi switches show 0 ohms.

12 volts on one of the wires at both low and hi switch, could not find the cold engine lockout switch.

forced the AC on by running a fused wire from battery to AC clutch, then to low switch, then ground. switches on dash at max AC, fan on, cold setting.

AC engaged and pressures took about 1 minute to settle at 215 hi and 25 low side with engine idling. the low switch did not cycle, not sure at what pressure it would open.

at that point the air in the dash vents was cold.

properly reassembly and AC not working again.

additional info, engine seems to run a bit cool, temp needle goes to low side of normal range, plenty of heat if selected. remember, regular t-stat system.

just took a ride up the interstate, good and warm now but no AC yet.

any ideas?
anybody know which relay runs the AC clutch?



edit: in hindsight the owners manual has the fuse and relay locations. the relay itself has the pin-out on its cover.

the wiring diagram helped a lot, I was able to apply a power jumper directly to the slot that powered the AC clutch. it worked.

thanks,
Perry

 

[RonD]

The computer(PCM) runs the AC in 2005

Pressure switches are the Ground for PCM AC "OK" detection, so if both switches are at 0 ohms then PCM sees good Ground.

PCM activates the AC relay in engine fuse box to activate compressor, compressor has its own fuse #25, 10 amp, in engine fuse box.
The AC relay's coil has/gets 12volts when key is on, but no Ground, the PCM passes on the pressure switch Ground to the AC relay to close it, which sends #25 fuse power to AC compressor

It also activates rad cooling fan with AC ON so I think PCM is activating AC relay, so could be bad relay or blown fuse


Diagram for 2005 2.3l below

 

[pjtoledo]

thanks.


contacts on the relay fried, cleaned them up to verify fix.
Advance Auto had relay 36126 in stock.


the wiffie is happy again!