No A/C, mechanics appear okay, clutch never turns on?

Tiny
SLEEPY HOLLOW
  • MEMBER
  • 1998 LINCOLN MARK VIII
  • 4.6L
  • V8
  • 2WD
  • AUTOMATIC
  • 167,000 MILES
The car sat for 4+ years in garage. I performed much DIY work to get it back on the road, registered and inspected. All fluids changed (including AT torque converter fluid drained). New front suspension components: Upper CAs, lower ball joints. Brakes good. DIY resurfaced rotors to remove glaze that was causing severe pulasation/shaking when stopping. New door lock actuators. New blend door actuator gives heat now.

Last issue - A/C will not turn on including with control set to max A/C. Clutch never engages. There is 35-40PSI in the system low side at 70 degrees ambient temperature. Self-test on control head passed, no fault codes. I cannot access the clutch coil connector from above or below without moving a bunch of A/C plumbing. So cannot energize directly to test. Compressor turns just fine by hand with engine off. I also have an OBDII+ Bluetooth scanner which shows A/C press switch at around 0.25V. States of clutch, cycling sw, med pressure sw, and driver request all show 0 when Max AC selected. Hypothesis: mechanics ok. Prob is in the control system. Cannot locate VLCM which controls clutch if I wanted to try energizing clutch from there. I must be blind. Wiring diagram shows VLCM in "front lower center of engine compartment" as last stop before clutch energizing on purple wire. What do you suggest for the next step? Thx.
Saturday, April 27th, 2024 AT 7:44 AM

5 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,328 POSTS
Hi,

The VLCM is on the right side of the engine compartment. See pic 3 below. Is that where you are looking? I ask because often people are looking toward the front near the radiator.

Also, I attached the wiring schematic. I'm not sure if you have it or not. Is the fuse indicated and highlighted good? It should have power at all times.

Let me know.

Joe

See pics below.
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Saturday, April 27th, 2024 AT 8:53 PM
Tiny
SLEEPY HOLLOW
  • MEMBER
  • 4 POSTS
Thank you for the suggestion on the VLCM location. I will check that today or tomorrow. Yes, I do have the diagram, thank you. Naturally I was looking where the diagram says it is as every other location checks out. But I also had several Mercury Grand Marquis in the past and the air suspension compressor is hidden right there (or opposite on the driver's side) as well if I recall correctly (and as your other diagram clearly shows).

I have checked the 40W #23 fuse and replaced it with its neighbor to be safe. Checked out fine. Will double check for power again and report back as I may only have checked continuity. Thanks.
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Sunday, April 28th, 2024 AT 8:32 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,328 POSTS
Hi:

Thank you for the update. It is a good idea to confirm there is power to and from the fuse, so let me know what you find.

Take care,

Joe
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Sunday, April 28th, 2024 AT 6:51 PM
Tiny
SLEEPY HOLLOW
  • MEMBER
  • 4 POSTS
Well, looks like I found the source of the problem: very bad mechanic.

I have been proceeding from the assumption that the system had enough pressure to kick the compressor on. I was wrong. To make a long story short, I decided to go back to square one and start over. I quickly discovered that I read the gauge wrong. The system had pressure but much less pressure than I thought. I started adding refrigerant and after several ounces of the 12oz can were dispensed, the compressor kicked on and began cycling every 3 seconds or so. I emptied the remaining contents into the system and the cycling is still going so I know it needs more. Capacity is 2 lbs according to the sticker. The temp from the vents went down about 8-10 degrees so I am feeling confident that it is cooling, but needs more refrigerant. I'll be getting that later today and will close this out with you all as soon as I have confirmed that this is indeed the problem.

In the meantime, please accept me apologies for sending us all on an unproductive line of diagnosis. I will say, though, I added significantly to my understanding of auto AC and also got intiimate with the Mark VIII AC besides during this exercise.

Thank you all for your help. It is much appreciated.
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Monday, April 29th, 2024 AT 10:16 AM
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 108,328 POSTS
Hi:

There is no need to apologize. That is an easy mistake and I wouldn't be truthful if I told you it never happened to me. LOL

Regardless, it does sound like you found the problem. I just hope there are no leaks that led to it. Take your time and let me know how things turn out for you.

Note: Make sure not to over charge the system. That will cause more problems. Chances are you don't need it, but here is a link you may find helpful.

https://www.2carpros.com/articles/air-conditioner-how-to-add-freon

Take care of yourself,

Joe
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Monday, April 29th, 2024 AT 7:05 PM

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