Hello All, I just picked up this truck with the 4.7 - auto - 4x4 and the A/C is not working. I evac'd and it held vac at 30" for 45+ mins. Tried to recharge but only got bout 6 oz. in system. Here's the thing when I turn it off there is power at both the pressure switches. When I turn on the a/c it losses power to both switches therefore the clutch doesn't engage etc. switches are at the dryer-low side and at the compressor-high side. Any help would be greatly appreciated. Thanks in advance.

 

It's working normally.

When the system is off you're reading battery voltage through the coil of the blower motor relay. When you energize the system, the PCM grounds the lead and you see no voltage, since you're downstream of the load.

Sheets 8W-42-4 and 8W-42-6 in the FSM.

What do you have for pressures in the system?

 

Thanks Dan. low side is about 70. hi side about 20. it took about 6oz 134 then stopped. clutch won't kick on but the aux fan comes on. thinking now that electrical part is ok maybe it's a blockage in the system.
Thanks again for ur help.

 

Yeah, your low side should stop around 40ish or so when full, at least thats where I stopped when I fully charged my system this week. I'd start by breaking the liquid line at the coupling and changing your orifice. Possibly, while you have it apart, flush everything except the compressor and accumulator, see if there is a blockage somewhere. Maybe even change the accumulator.

 

20 on the high side? Or is that 200?

Still, the clutch should be engaging. I'd at least try to get the clutch engaged to see what the pressures are running.

At the relay you should have 12v on pins 86 and 85 (coil side). The switch side is pins 30 and 87. Try swapping out the relay, maybe with the horn relay.

The PCM controls the clutch via this relay in the PDC. Power is via 2 fuses, #7 (10 amp) and #10 (20 amp) in the junction block, one is for the relay and the other for the clutch itself.

The high pressure switch contacts should close between 270-330 and open between 450-490 psi.
The low pressure switch contacts should close at 39 and open at 24 psi.

Relay pinout:

If you look at it so that the 3 terminals are horizontal, the outside 2 horizontal terminals are the coil. The 2 vertical terminals, and the middle horizontal terminal are the switch. The outside vertical terminal is the common, the inside vertical is NO, the middle horizontal, NC.

Jump the two vertical terminals and the clutch should engage.

 

I have one for you guys,Why does my a/c have a full charge according to my guage and when it is on the normal a/c setting it blows out mildly low cold air with a weird smell even when you turn the fan all the way up,but when i put it on Max a/c the thing blows out freezing cold air on every fan setting? it's got me puzzled because i hear the doors opening and closing in the dash through all of the settings wether its heat,defrost or just outside air,thanks for the help bro's.

 

The smell could be from debris that has accumulated in the a/c housing over the years. As to the temp, what's the outside ambient temp when this is happening?

 

Probably the same high humidity and 90 + degree weather your having in Mass.(Im in Pennsylvania) Should i try and change the cabin filter for the a/c and where is it?

 

There is no cabin filter in the Dakota, at least not in 2000. They do sell cleaners that you spray into the intake to get rid of "crap." I don't know how effective it would be though. Any junk probably won't get through the evaporator drain.

Yeah my folks are in State College, it's been hot as blazes there too. 107 yesterday for them, I saw 106 here.

FYI, I used Max a/c yesterday too. It was just too hot not too. I mean the air was cool, but not cold. In Max, I froze my *ss off!

 

State College is sweet,the Appalachian Mountains are a must see from west to east here,thanks for the reply,im going in for a front end alignment this week so im gonna ask my mechanic about that crap cleaner,have a good weekend bro.