Pesky A/C Clutch

Bar94Bronco

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Hi Guys,

I recently bought a 1994 Bronco XLT

The AC was not running when i got it and i decided to make that my little project.
After taking it 2 two mechanics i have replaced the following parts

(in order)
AC Dryer
Pressure switch
Vacuum line behind the dryer for the ac (back left)
Condensor
Ac Compressor/Clutch

I assumed the Clutch was getting power because both mechanics said there was power on the line. When i went to test the compressor/clutch it still is not engaging. I filled up the PAG 46 to the correct amount for the system (7oz).
When I attached the power from the battery to the Compressor, the clutch engaged.

So now im starting to think I there is no power coming from the lines.
I replaced most of the smaller fuses under the steering wheel and in the power distribution box

Any suggestions on what i should try and check next?
and how to check it.
Does anyone know how to test the Clutch plug with a Multi Meter?

Im in Texas heat and thought i would have this resolved by now lol


Thanks everyone
 

Tiha

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AC can be tricky.

How much pressure is in the system?
If the pressure is low then the low pressure switch will prevent the compressor from coming on.

You really need a set of gauges.
 

Motech

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Disconnect and jumper that pressure switch connector while running with AC turned on.
  • If clutch engages, you either have a faulty switch or no pressure.
  • If it does not, you have a circuit problem somewhere.
Don't forget to check your fuses.
 
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Bar94Bronco

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AC can be tricky.

How much pressure is in the system?
If the pressure is low then the low pressure switch will prevent the compressor from coming on.

You really need a set of gauges.
I got a manifold guages and low side is reading in the 50 range and high side is on the 100 side. I jumped the clutch from the battery and it worked then.
 
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Bar94Bronco

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Disconnect and jumper that pressure switch connector while running with AC turned on.
  • If clutch engages, you either have a faulty switch or no pressure.
  • If it does not, you have a circuit problem somewhere.
Don't forget to check your fuses.
For the switch youre saying to unplug the power and use jumper cables on that yes?

I will try that today to see if i get a change.
 

Tiha

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Picture,

If you jumper with a paperclip the compressor should come on.

If it does the pressure is too low. Or low pressure switch is bad.

Did you pull a vacuum on the system before charging it?
 

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Bar94Bronco

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Picture,

If you jumper with a paperclip the compressor should come on.

If it does the pressure is too low. Or low pressure switch is bad.

Did you pull a vacuum on the system before charging it?
I haven’t vacuumed it after I put the parts on, I’m trying to get the compressor to kick on before I charge it again


It on in the picture and the compressor still isn’t kicking on

So I take it the pressure switch isn’t bad?

Does that mean that the cords in the compressor might be bad?


I tested voltage and I get power when I ground to metal
When I ground to the plug ground, I don’t get any power
 

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Tiha

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Yes clutch should be running now. So AC clutch relay? Fuse maybe?
 
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Bar94Bronco

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Yes clutch should be running now. So AC clutch relay? Fuse maybe?
Checked all fuses and they’re in tack.

I’m assuming it’s the 6th fuse under the steering wheel, don’t know what fuse on the box but those fuses are all good condition too
 

Tiha

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Yep looks like that is the fuse.

Do you have 12 volts at one side of the low pressure switch?

If you do, move onto the high pressure switch, usually mounted on the back of the AC compressor, see if you have 12 volts there.
 

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Bar94Bronco

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Yep looks like that is the fuse.

Do you have 12 volts at one side of the low pressure switch?

If you do, move onto the high pressure switch, usually mounted on the back of the AC compressor, see if you have 12 volts there.
Low pressure switch gets some voltage multimeter set 2 volts and flutters at .01/.02)
and high barely gets any, at 2 volts with the jumper
.001/.002
Pressure switch Plugged in same effect
Flutters

Thank you for your help so far
 

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termy1971

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It's not charged? Put gauges on it. Start charging it. The compressor should come on. It will not run with out any pressure. If it doesn't come on jump it and start charging it. Some times they need initially need to be jumped to start charging.
 

Tiha

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Low pressure switch gets some voltage multimeter set 2 volts and flutters at .01/.02)
and high barely gets any, at 2 volts with the jumper
.001/.002
Pressure switch Plugged in same effect
Flutters

Thank you for your help so far
just check for 12 volts to ground, Not across the harness.

One side of the plug should show 12 volts.

Red lead to plug,
Black lead to negative battery terminal, or other ground.
 
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Bar94Bronco

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just check for 12 volts to ground, Not across the harness.

One side of the plug should show 12 volts.

Red lead to plug,
Black lead to negative battery terminal, or other ground.
This is with the pressure switched jumped and the car on
Ac on full blast
 

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Bar94Bronco

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It's not charged? Put gauges on it. Start charging it. The compressor should come on. It will not run with out any pressure. If it doesn't come on jump it and start charging it. Some times they need initially need to be jumped to start charging.
It was charged prior, and didnt come on. I jumped the battery to the ac compressor and that worked, then i bridged the pressure switch and it will not turn on
The compressor, condensor, dryer, pressure switch and orfice tube are all new.
 

96XLT

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I haven’t vacuumed it after I put the parts on, I’m trying to get the compressor to kick on before I charge it again
That is a bad idea to run the compressor without refrigerant and it is why you are not able to get the AC to turn on in the first place. The AC system is designed to protect the compressor by not operating when the refrigerant is not sufficiently charged.

To test the wiring/electrical without charging the AC system, I would suggest removing the wire harness from the clutch and testing for 12V at the clutch wire harness after jumping the low (clutch cycling) pressure switch. That way you will not damage the compressor or other components by running it without refrigerant.

Typically you test for leaks with vacuum after part replacement, if it holds for 30 minutes or longer, the system should hold a charge. Occasionally high pressure during operation will show a leak not found through a vacuum test. Once charged, you can operate the AC and test functionality, pressures, etc.

I would also question why you added 7 oz of PAG oil as you didn't mention flushing out all of the old oil. For a 94 Bronco, a google search showed 7 oz is total PAG oil capacity listed and the oil tends to pool in each AC component. The amount of oil needed in each replaced part is typically obtained from the Ford service manual or standard guidelines, example https://www.aa1car.com/library/pagoil.htm#:~:text=oil capacities. Replacement compressors usually contain oil, so it is typical to only add oil to other replaced components. I would refer to the compressor's manufacturer for oil recommendations (if you need to add). Note: it is stated too little oil can cause compressor failure and too much oil affects AC performance.

Good luck with your repair.
 
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Tiha

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This is with the pressure switched jumped and the car on
Ac on full blast
What plug is that? High pressure switch?

If that is the case, doesn't sound like you are getting 12 volts to the low pressure switch.

If that is the case then have to check the switch in the dash? I guess.
 
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Bar94Bronco

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That is a bad idea to run the compressor without refrigerant and it is why you are not able to get the AC to turn on in the first place. The AC system is designed to protect the compressor by not operating when the refrigerant is not sufficiently charged.

To test the wiring/electrical without charging the AC system, I would suggest removing the wire harness from the clutch and testing for 12V at the clutch wire harness after jumping the low (clutch cycling) pressure switch. That way you will not damage the compressor or other components by running it without refrigerant.

Typically you test for leaks with vacuum after part replacement, if it holds for 30 minutes or longer, the system should hold a charge. Occasionally high pressure during operation will show a leak not found through a vacuum test. Once charged, you can operate the AC and test functionality, pressures, etc.

I would also question why you added 7 oz of PAG oil as you didn't mention flushing out all of the old oil. For a 94 Bronco, a google search showed 7 oz is total PAG oil capacity listed and the oil tends to pool in each AC component. The amount of oil needed in each replaced part is typically obtained from the Ford service manual or standard guidelines, example https://www.aa1car.com/library/pagoil.htm#:~:text=oil capacities. Replacement compressors usually contain oil, so it is typical to only add oil to other replaced components. I would refer to the compressor's manufacturer for oil recommendations (if you need to add). Note: it is stated too little oil can cause compressor failure and too much oil affects AC performance.

Good luck with your repair.
Hi thank you for the response

Let me clarify

I charged it with ac can refrigerant, but I did not vaccuum the system. Once it is functioning i am going to take it to be vacuumed and filled
I took the car to a mechanic first and they verified there werent any leaks in the system, and it hold refrigerant fine

The additional Pag oil added was 1.6 oz of fluid per the Compressor part requirement, this totaled to 7.0oz of fluid for the compressor.
Now i understand what your saying about old fuild in the line, but when i removed the old compressor, there wasnt any oil in it so i assumed there was none in the line (i could be wrong)

Which leads me to 2 conclusions here, I may have added too much 1.6 (a total 7.0 oz) or there is not enough in the system because the previous compressor was dry.


And for this part
"To test the wiring/electrical without charging the AC system, I would suggest removing the wire harness from the clutch and testing for 12V at the clutch wire harness after jumping the low (clutch cycling) pressure switch. That way you will not damage the compressor or other components by running it without refrigerant."
I want to make sure im understanding
(Current state, everything is plugged in)
-Remove the Power source from the AC Compressor (the plug on the top left behind the AC clutch)
- Remove the Pressure switch (at the dryer) and jump the connection
- test the Ac Compressor Plug for 12

If that is correct, i have done that and replied to Tiha, im only getting .01 reading
If not, can you clarify a little more?

thank you for your help
 
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Bar94Bronco

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What plug is that? High pressure switch?

If that is the case, doesn't sound like you are getting 12 volts to the low pressure switch.

If that is the case then have to check the switch in the dash? I guess.
its the cord on the back of the compressor that is connected to the ports that plug into the back of the compressor
Which i believe is the high pressure switch

and for switch in the dash, do you mean the actual controls i use in the car? those seemed to be working, but im gonna check them again for good measure
 

Tiha

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Attached is the diagram.

Power goes from fues to dash switch, to low pressure switch, to high pressure switch to compressor clutch.

Just have to follow it back to the origin.

With the switch in normal or max AC the pink wire should have power on it.

There should be a brown wire with white stripe going into the switch that should have power on it.
 

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