AC Clutch not engaging without jumping

acreature · Nov 24, 2018

1996 XLT 4.0 4wd fixer-upper purchase

Got suspension repaired, the motor running as it should, now to tackle the AC.

Clutch does not engage when switched to AC. Will not take freon without clutch engaged. All fuses are good, WOT relay is good.

Clutch will engage when jumped at the compressor, but will still not take freon when done so.

Tested the plugs to the pressure switches (high and low) and get no voltage (if I did it correctly). This is where I am lost without guidance, as to where to go next. As far as testing the switches/sensors themselves, I felt was moot since I did not get and voltage to the pigtails.

Any step by step help would be greatly appreciated.

RonD · Nov 24, 2018

Fuse #18(15amp) in cab fuse box powers the AC compressor, key on power

This 12volts runs to the Selector switch in the cab, and the switch sends out the 12v when in Defrost or AC on/max positions

The 12v travels from the selector switch and thru the low and high pressure switches then thru the WOT AC relay and to the compressor

So with key on(engine off), and selector on AC you should have 12v on 1 wire at cycling pressure switch, its on the Accumulator(black tank near firewall)
If cycling switch is passing voltage(closed) then that 12v will pass to the Pressure switch, then from there to the WOT Relay
WOT relay is connected so it passes the 12v to compressor when it is OFF, Computer Grounds this relay, activates it, to cut off 12v to compressor when extra engine power is needed.

Turn selector to OFF
Pull out the WOT Relay then turn on the key
Test each slot in relay's base, only one should show 12v, thats the 12v for the relays coil
Move selector to AC On
There should now be a second slot in the base with 12v, that's the 12v from fuse #18 passing thru selector switch and pressure switches to the Relay, so all is well up to that point.

And just a heads up on the way the WOT relay might work, with key on engine off the computer may Ground the WOT relay to cut power to AC compressor for start up, this is normal, once computer sees RPMs above 400, engine started, it should unGround relay to send 12v to compressor, if AC/Defrost is on

Denisefwd93 · Nov 24, 2018

just jumper the low pressure switch or direct wire ac clutch, start engine, if you feel cooling you probably are close to where you need to be, but like most systems, it's probably low on refrigerant.

A system can be charged without the compressor running but we can go into that another time.

For now, jumper,start, check, don't tear the system apart unless you are sure it has bigger problems,

also if it is cool or cold outside the compressor may not engage or short cycle, with refrigerant in it because the pressure is may not be high enough to close the switch.

acreature · Nov 24, 2018

RonD said:
Fuse #18(15amp) in cab fuse box powers the AC compressor, key on power

This 12volts runs to the Selector switch in the cab, and the switch sends out the 12v when in Defrost or AC on/max positions

The 12v travels from the selector switch and thru the low and high pressure switches then thru the WOT AC relay and to the compressor

So with key on(engine off), and selector on AC you should have 12v on 1 wire at cycling pressure switch, its on the Accumulator(black tank near firewall)
If cycling switch is passing voltage(closed) then that 12v will pass to the Pressure switch, then from there to the WOT Relay
WOT relay is connected so it passes the 12v to compressor when it is OFF, Computer Grounds this relay, activates it, to cut off 12v to compressor when extra engine power is needed.

Turn selector to OFF
Pull out the WOT Relay then turn on the key
Test each slot in relay's base, only one should show 12v, thats the 12v for the relays coil
Move selector to AC On
There should now be a second slot in the base with 12v, that's the 12v from fuse #18 passing thru selector switch and pressure switches to the Relay, so all is well up to that point.

And just a heads up on the way the WOT relay might work, with key on engine off the computer may Ground the WOT relay to cut power to AC compressor for start up, this is normal, once computer sees RPMs above 400, engine started, it should unGround relay to send 12v to compressor, if AC/Defrost is on

As soon as the rain stops, I will go through this testing and post results. Thank you.

acreature · Nov 24, 2018

Denisefwd93 said:
just jumper the low pressure switch or direct wire ac clutch, start engine, if you feel cooling you probably are close to where you need to be, but like most systems, it's probably low on refrigerant.

A system can be charged without the compressor running but we can go into that another time.

For now, jumper,start, check, don't tear the system apart unless you are sure it has bigger problems,

also if it is cool or cold outside the compressor may not engage or short cycle, with refrigerant in it because the pressure is may not be high enough to close the switch.

I strongly agree on refrigerant (coupled with my not getting my hands on a true AC gauge set to verify). I got the clutch to engage via jumping her at the compressor, but she still wouldn't take any freon. Still, with AC off, pressure sits at about 12lbs via the shitty gauge that comes with a can of refrigerant.

Denisefwd93 · Nov 24, 2018

static pressure.. just check the pressure of a can that is at the same outdoor temp as the truck. the static pressure of a charged system should be about the same. static meaning sitting still, not in operation.

You can warm the can/s in hot water, connect to the high side and "dump" it in with the can upside down NEVER add Liquid refrigerant to the low side. (although on most automotive systems the low side usually is usually before the accumulator it's still better to not add liquid R to the low side.)

the high side connection on older rangers is a poppet, that looks like a rubber ball. they tend to leak and get worse when used for checking pressures.. New ac hoses for the system aren't expensive.

12lbs would mean the outdoor temperature is about 10 degrees.

Your gauges are a temperature pressure chart it's just done in a circle with a needle, if you look at a card chart you'll see the same pressure and temperature relationships.

An example would be, 50° Outdoors = about 45 lb static

acreature · Nov 24, 2018

RonD said:
Fuse #18(15amp) in cab fuse box powers the AC compressor, key on power

This 12volts runs to the Selector switch in the cab, and the switch sends out the 12v when in Defrost or AC on/max positions

The 12v travels from the selector switch and thru the low and high pressure switches then thru the WOT AC relay and to the compressor

So with key on(engine off), and selector on AC you should have 12v on 1 wire at cycling pressure switch, its on the Accumulator(black tank near firewall)
If cycling switch is passing voltage(closed) then that 12v will pass to the Pressure switch, then from there to the WOT Relay
WOT relay is connected so it passes the 12v to compressor when it is OFF, Computer Grounds this relay, activates it, to cut off 12v to compressor when extra engine power is needed.

Turn selector to OFF
Pull out the WOT Relay then turn on the key
Test each slot in relay's base, only one should show 12v, thats the 12v for the relays coil
Move selector to AC On
There should now be a second slot in the base with 12v, that's the 12v from fuse #18 passing thru selector switch and pressure switches to the Relay, so all is well up to that point.

And just a heads up on the way the WOT relay might work, with key on engine off the computer may Ground the WOT relay to cut power to AC compressor for start up, this is normal, once computer sees RPMs above 400, engine started, it should unGround relay to send 12v to compressor, if AC/Defrost is on

Key on, engine off, AC on - 12v at pressure switch at Accumulator. 12v at #85 for WOT relay.

Relay out, key on, AC off - #85 shows 12v
Relay out, key on, AC on - only #85 shows 12v

Interior dash Fuse #18 is good .

As an aside, the relay, whether AC is on or off, sounds to engage when placed back on Power Distribution Box under the hood.

edit* I'll have to recheck, but there, by memory, was no 12V @ the pressure switch located at the compressor... if that was part of your testing procedure?

RonD · Nov 24, 2018

Yes, pressure switch at compressor is OPEN so you have a pressure issue or bad pressure switch.
You can place a jumper inside the connector to bypass it temporarily, but.........
The compressor needs OIL circulating or it will burn out, the oil is in the "freon", the pressure switches are there to prevent system from "blowing up" i.e. high pressure from blockage, and from low pressure i.e. low "freon" levels which would burn out compressor from lack of oiling.

Slots 85 and 86 are the relays Coil, if 85 has 12v key on then 86 will run to computer so it would ground 86 to turn relay on, disconnection AC compressor from power

87A or 30 are the slots that would be connected to last pressure switch, the one at the compressor.
Ford could have used 30 for the switched power and 87A for "out to compressor" or visa versa it will work either way
87 would not be used

fuse18------selector switch------cycle switch-------------pressure switch(compressor)--------WOT relay--------AC Compressor

acreature · Nov 24, 2018

RonD said:
Yes, pressure switch at compressor is OPEN so you have a pressure issue or bad pressure switch.
You can place a jumper inside the connector to bypass it temporarily, but.........
The compressor needs OIL circulating or it will burn out, the oil is in the "freon", the pressure switches are there to prevent system from "blowing up" i.e. high pressure from blockage, and from low pressure i.e. low "freon" levels which would burn out compressor from lack of oiling.

Slots 85 and 86 are the relays Coil, if 85 has 12v key on then 86 will run to computer so it would ground 86 to turn relay on, disconnection AC compressor from power

87A or 30 are the slots that would be connected to last pressure switch, the one at the compressor.
Ford could have used 30 for the switched power and 87A for "out to compressor" or visa versa it will work either way
87 would not be used

fuse18------selector switch------cycle switch-------------pressure switch(compressor)--------WOT relay--------AC Compressor

With engine and AC on, I have 12v at the pigtail for the switch at the accumulator, but do not have 12v at the pigtail for the compressor... What is next? Wiring checks?

Thank you, very much.

RonD · Nov 24, 2018

Oops then Cycle switch is open, put jumper in that "pigtail" then see if you have 12v at Compressor switch pigtail, if so then wire between them is OK

Then put compressor pigtail back on its switch and check for the second 12v slot at WOT relay base, if its there then compressor pressure switch is closed, so OK

acreature · Nov 24, 2018

Denisefwd93 said:
static pressure.. just check the pressure of a can that is at the same outdoor temp as the truck. the static pressure of a charged system should be about the same. static meaning sitting still, not in operation.

You can warm the can/s in hot water, connect to the high side and "dump" it in with the can upside down NEVER add Liquid refrigerant to the low side. (although on most automotive systems the low side usually is usually before the accumulator it's still better to not add liquid R to the low side.)

the high side connection on older rangers is a poppet, that looks like a rubber ball. they tend to leak and get worse when used for checking pressures.. New ac hoses for the system aren't expensive.

12lbs would mean the outdoor temperature is about 10 degrees.

Your gauges are a temperature pressure chart it's just done in a circle with a needle, if you look at a card chart you'll see the same pressure and temperature relationships.

An example would be, 50° Outdoors = about 45 lb static

60-65f degrees here at the time.

acreature · Nov 24, 2018

RonD said:
Oops then Cycle switch is open, put jumper in that "pigtail" then see if you have 12v at Compressor switch pigtail, if so then wire between them is OK

Then put compressor pigtail back on its switch and check for the second 12v slot at WOT relay base, if its there then compressor pressure switch is closed, so OK

Okay, I apologize, as you've lost me.

Pigtail, meaning pigtail at Compressor? (sorry, which wire)... "Compressor Switch Pigtail" (Switch/Sensor or Clutch pigtail?)

Plug the compressor switch back on, then check for a secondary 12v at the WOT in the power distribution box (w/ relay out)?

I am trying hard to keep up, haha

Denisefwd93 · Nov 24, 2018

You and Ron talk about the electrical but, if the system is low on refrigerant it will short cycle or not run.

At 60-65 degrees Outdoors the system pressure when not running should be around 57-65 ish

acreature · Nov 24, 2018

Denisefwd93 said:
You and Ron talk about the electrical but, if the system is low on refrigerant it will short cycle or not run.

At 60-65 degrees Outdoors the system pressure when not running should be around 57-65 ish

So, I should jump the low pressure switch to get freon in? If so, which wire, as I am not too keen on shorting the system. lol

As an aside, it isn't short cycling, as I am aware... no clutch engagement at all.

Denisefwd93 · Nov 24, 2018

It's not proper to advise you to put refrigerant into a system that is leaking (even though we know everybody does and probably why 134 is so loosely) controlled.) I would just warm up the can and put the refrigerant in the system when it's not running, it will go in as long as the refrigerant can is warmer than system. You also get a little pressure can of refrigerant oil to add to the system. This is the best we can do without knowing the history of your system. When you jump pressure controls your not shorting out the system, you are just overriding that particular control. The cycling control also is a pressure control and I believe it cuts out around 35 lb,. The high pressure control on the small discharge line near the compressor cuts out around 400 there is also a safety relief valve on the back of the compressor it looks like a little brass button thingy

AC Clutch not engaging without jumping

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