A/C compressor does not engage?

1991 FORD F-150
135,000 MILES • 5.0L • V8 • 4WD • AUTOMATIC
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LWOLFGRAM
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Fuse is good.
The A/C clutch only engages when I jump the low-pressure switch.

I've replaced the switch and there is power to the purple wire.
I've vacuumed the system and have 20lbs. of pressure on my gages but still no clutch engagement.

I'm using Vevor gages and manifold to monitor high and low side pressure. When I pull vacuum the high (red) gage gives me 28lbs. Of vacuum. The low (blue suction side) gives me about 10 lbs of vacuum.

Any ideas?
Jul 1, 2024 at 4:03 AM
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LWOLFGRAM
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I'm using Vevor gages and manifold to monitor high and low side pressure. When I pull vacuum the high (red) gage gives me 28lbs. of vacuum. The low (blue suction side ) gives me about 10 lbs of vacuum.
Jul 1, 2024 at 4:12 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,238 POSTS
20 pounds on the low side is not enough to trigger the low side pressure switch. I would start the engine and turn the A/C system on full, then open the refrigerant can until you see about 50 psi and see if the clutch engages. Here is a video to help you see what I am talking about:

https://youtu.be/4EqdrBVb0sY?si=W--MMBN0CHo2Twjq

Please go over this guide and get back to us.
Jul 1, 2024 at 4:46 AM
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LWOLFGRAM
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I can’t get the system (low side) to take freon.
Jul 2, 2024 at 1:47 AM
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STRAILER
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Is the system off when you are trying to add refrigerant? Also, when you turn the refrigerant source on to fill the system does the gauge go up to about 60 PSI?
Jul 2, 2024 at 2:57 AM
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LWOLFGRAM
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System is on, gauge goes to about 20 lbs.
Jul 2, 2024 at 5:06 AM
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STRAILER
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Then the refrigerant recharge container is low. Ambient pressure in warm weather should be about 65 to 75 psi. Cans or Keg
Jul 2, 2024 at 8:36 AM
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LWOLFGRAM
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I’ve tried three different cans with three different Freon applicators. Could the office tube be clogged? Would that prevent Freon from entering the system?
Jul 2, 2024 at 10:47 AM
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STRAILER
  • ✓Experienced Mechanic
  • 55,238 POSTS
With the system off you should have about 60 PSI on the high and low side. It sounds like there is a problem with the service valve, is the Schrader valve broken or sunken down inside the port? Can you upload some images or short video? The orifice is irrelevant when the system is off.
Jul 3, 2024 at 6:23 AM
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