My AC quit all at once, I have verified that the compressor clutch is not engaging. I understand this "could" be low refrigerant, or many other causes. I got a set of HF gauges and have verified that I have some refrigerant in the system but realize from my research that showing static pressure does not necessarily mean that there is a proper charge. I'd like to try to override and engage the compressor clutch, both to just verify that it is functional, and to help pull some refrigerant into the system through the low side. The clutch has a 2 wire plug with a brown/brown with white stripe. Can I run 12V directly to this plug to engage the clutch? Any other thoughts on troubleshooting this? I love my 2006 Ranger; 166k miles and the engine purrs better than new. I want to drive it for many more miles but financially it is not a good candidate for an expensive AC repair at a garage.

 

Welcome to the forum

Not seeing a Brown wire at the field coil(AC compressor clutch)

On my 2006 wiring diagram I see a 12v Grey with white stripe wire and a Black Ground wire

Yes, you can test if the compressors clutch works by applying 12v to the 12v side of the clutch, you should hear a click and see clutch plate move a bit
Then you can start the engine and try it with engine running

AC system has a high pressure switch and a low pressure switch, if either OPENS then no 12v to compressor's clutch
Reason is, if pressure is too high then AC lines will explode at weakest point, if pressure is too low then compressor will run out of oil and burn up, the fluid used in AC system has oil in it for the compressor to stay lubed.

The AC system control runs thru the computer(PCM)
When you turn on AC on the cab's panel that signal goes to the PCM
PCM checks engine temp, if not over heating then it uses Pressure Switch Ground to activate AC Relay in engine fuse box
AC relay closes and sends 12v from FUSE #25, 10amp, to AC clutch, Fuse #25 is in engine fuse box, check that it is good

Pressure switches are hooked up in series
Ground----------high pressure-----------------low pressure------------------------PCM(computer)

So the Ground passes thru each switch to the PCM, not 12v
If either switch OPENS then no Ground at PCM so no Ground for AC Relay and no 12v for AC clutch

That's for Rangers with V6 engines, 4cyl is slightly different but not that much, so you should always include engine size along with year of Ranger

 

Wow: Thanks for the prompt and concise response! Yes, this is a 4.0 engine. I think you're correct about the wire colors, it was getting dark when I looked at them last night. I checked the #10 fuse as you suggested and it tested OK. I also found the relay associated with the clutch and checked it by swapping it with another one with the same number and had no change.

What I can't get my head around is how the refrigerant works with the pressure switches. I watched one video that showed that the static pressure on the gauges would read a pressure related to the temperature, whether the system was properly filled, or only had 3 oz. of refrigerant in it. Both high and low side would read the same (in my case 90psi) after it equalized. If I am understanding how this works, if the charge was low, the compressor would start running but quickly shut off as the low side pressure would drop below the setting of the pressure switch. If the charge was too high, the compressor would start, then shut down because the high side pressure switch would then see too high a pressure.

I am going to try to figure out a way to get 12v to the clutch to see if it will come in. The tabs on the clutch connection are too close together for me to get alligator clips on without touching, I will probably try to just cut the wires to the plug and tie in there.

I have located the high and low pressure switches. Would there be a way to check these, either by unplugging, reading continuity, or jumping them to ground etc.?

How many miles on your 2006?

 

Oops, meant to say #25, 10 amp fuse

 

I had an intermittent problem with my AC. It turned out to be a spacer that, due to parts wear, was now to thick to keep the clutch engaged (heated up and disengaged due to parts expansion). This guy explains it well I bought a kit from Autozone, put in a thinner spacer and no problems since.

 

Don't have a 2006, but do have wiring diagrams :)

You can remove the connector on a pressure switch and put a jumper inside the connector, so it passes the GROUND like a closed switch should do
Or you can use an OHM meter and touch meters probes to the switch's two contacts, should Read 0 ohms if switch is Closed, same as touching meters probes together shows 0 ohms

All AC, car or home or refrigerator, works the same way
Refrigerant is compressed, this heats it up very hot and vaporizes some of it, it is then passed thru a Condenser(in front of the radiator on vehicles), this cools it a bit, enough to turn any vapor back into a liquid, it is then sent to a Receiver/dryer, this holds the hot high pressure liquid and draws out any moister(dryer)
Hot high pressure fluid is then sent thru an Expansion valve, when the hot high pressure fluid is allowed "decompress"/Expand, drop in pressure, the heat stored in the fluid drops in tempurature rapidly releasing the stored energy.
This now VERY cold low pressure fluid goes thru the Evaporator, which is what cools the air the blower fan circulates in the vehicle.
From the Evaporator the now low pressure fluid flows back to the Compressor to start its trip through the system again.

Compressor>>>>Condenser>>>>Receiver/dryer>>>>>Expansion Valve>>>>Evaporator>>>>>Compressor

And thats AC for any AC system

Compressor to Expansion valve is the High side of the system
Expansion valve to Compressor is the Low side of the system

OUTSIDE AIR TEMPERATURE!!!
This is VERY VERY important when reading AC internal pressures
Chart here: R-134a System Pressure Chart - AC Pro<?php/* bloginfo('name'); */?>

You can see it varies quite a bit depending on outside temp

 

Have a little progress to report and maybe some good news. I was able to get some clips on the clutch connection so I could run it directly off my battery. Clutch engages, compressor turns, and I am getting some (not great) cool air from the registers. I hooked my gauges up and was showing about 38 low, 68 high, at about 80 degrees F. According to the chart on the link supplied by RonD, I am still low on refrigerant (but also maybe weak compressor).

How often should your clutch cycle in normal conditions?. I remember that for the last few years, the clutch cycled every 4 or 5 seconds. I never thought anything about it but I am wondering now if I have been marginally low on refrigerant for a while.

RonD. The charts you supplied were very helpful. I still haven't been able to test the pressure switches as you described so I am probably doing something wrong. I couldn't get EITHER low or high switch to show continuity with the plug disconnected using my multimeter set to ohms. I don't think there's a likelihood that they both failed at the same time so it's probably something I am doing wrong. I haven't yet tried to jump these out. You mentioned that overheating could keep this from working. I am showing normal temps on my dashboard gauge but was wondering if there is another sensor that could be showing hot and preventing this from working?

TimKresge: Thanks for the very interesting video. I don't think it's my problem this time, but may well be an issue in the future since I have high mileage, so I will file this for future reference. I never really even knew how this clutch worked so was happy to get an understanding of it. I then watched some other videos showing complete removal and repairs on the clutch. It looks like something doable, but maybe difficult with the compressor on the vehicle.

I'll make sure I continue to post on this as I wind my way through the troubleshooting.

 

80degF outside temp

38psi low side would mean switch is OPEN, needs to be 40-50psi
68psi high side???? also OPEN and VERY VERY LOW

Low side pressure will be high engine and AC OFF, after AC/compressor is turned on Low Side will drop 10-15psi, or more

Video here: www.youtube.com/watch?v=gut79biRD5Y

When AC is off but fan is on or Defrost is selected the compressor will cycle on and off, it is used to Dry the Air in the cab.

When AC is on the compressor will not cycle on and off it will stay on unless a pressure switch OPENS and shuts it off.

2006 temp gauge info comes from the computer so both use one sensor

Low pressure side tells you if refrigerant is low
High Pressure side tells you if there is a blockage in the system

 

I was able to run the compressor long enough by applying 12v to it to add the remains of a bottle of refrigerant while watching the high side gauge. High side got up to about 140 psi at about 80 degrees. I was able to verify that both the high side and low side pressure switches were closed while the compressor was running with a multimeter, I also jumped both of the pressure switches out. I still did not have 12v to the plug that goes in the clutch. My next steps:

Figure out a way to check if it could be the controls in the cab not "telling it" to come on

I keep reading about a WOT relay that could stop this from working, don't know if my truck has one or if so where it is and how to check it?.

 

You have an AC relay in 2006, that is the same as WOT(wide open throttle) Relay on older models that didn't have computer controlling AC system

Computer would OPEN WOT relay when driver pushed gas pedal down to the floor, turning off compressor to give drive maximum power for passing or just acceleration
In 2006 computer would OPEN AC Relay

With key on engine off have someone turn AC on and off and see if AC rely is clicking, put your finger on it
Then try samething with engine running

If AC relay is not clicking OPEN and CLOSED then thats the problem with compressor power
Pull out relay
Get volt meter
Key OFF
Test each slot for the relay for 12volts
You should find only 1, thats the 12v from fuse #25 in engine fuse box
Remember that slot
Turn key ON
There should now be one more slot with 12v, thats the 12v from PCM relay

If both check out then problem is PCM is not Grounding the AC Relay

 

Thanks for sticking with this problem! It looks like I have a bad relay. I had switched relays earlier in the process but the diagram I was accessing at that time gave a different relay number than the one I accessed today. I took out the adjoining relay (windshield washer pump) and put it in the clutch spot and the clutch started working properly. I now have AC!!

I've learned so much from this process and want to thank you again. I've seen your name on several other AC posts so you have shared your knowledge many times and helped many people. I am better off from the experience, I have a set of gauges to use in the future or share with others, I know much more about how these systems work, and know how to charge my vehicle. I haven't ever had a relay go bad but will get some spares to keep with me, as well as printing off the fuse box diagram to keep in the vehicle, looks like many of the other relays could shut you down if they failed.

 

Good work

Many don't stick with it, you did and found the problem

 

I had mistakenly looked at the 2.3 engine fuse diagram. The location for the AC clutch relay is 46A on my 4.0.