My A/C isn't working, I've replaced almost everything.

[Noobular]

I've replaced the Compressor, high and low pressure sensors, the other sensor in the compressor and my AC still won't work, when doing all this, I refill the Freon it hits 40lbs and the clutch just wont engage.
If I manually unplug the low pressure sensor and make the connections touch with an alligator clip into the connector it will engage the clutch on the compressor. at this point I don't know what's wrong.
The A/C control module in the cab does function and display (seemingly) as it should. any help would be greatly appreciated.

The only things I haven't replaced are the lines and the dryer itself

 

[Orpedcrow]

You’ll have to have a manifold set at least so you can see pressures on both sides. If there’s clog, orifice tube being full of aluminum from compressor failure as an example, you’ll have way to much pressure on one side and low pressure on the other.

Here’s an example of an inexpensive gauge set.

https://www.harborfreight.com/r134a-ac-manifold-gauge-set-58776.html

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[Orpedcrow]

Here’s a couple reference charts I use.

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[scott2093]

Not sure what vehicle we're talking about but , with mine, I wouldn't rule out the control/head unit...there are simple enough tests to verify it and relays are doing their job....

 

[HotrodZ06]

If you jumper the low side cycling switch on the accumulator and the clutch engages the rest of the circuit is working to include the control head. I would look at the cycling switch and verify pressures as referenced by Orpedcrow.

 

[GoToGuy]

You've seen it before make, model, year, all ac options it's equipped with.

 

[Schurkey]

I refill the Freon it hits 40lbs

How many actual pounds of refrigerant have you installed?

"40 psi" doesn't tell us much.

As said, you need to know low- and high-side pressures, and you need to know how much refrigerant the system is supposed to take, and how much you've put in.

And, of course, you vacuumed the system prior to adding refrigerant...right?

In general, opening the system and NOT replacing the orifice tube and the receiver/dryer/accumulator is a big mistake. You have no idea if the orifice tube screen is plugged, or if the desiccant bag is saturated with moisture.

 

[GoToGuy]

Well?

 

[Noobular]

Sorry I've been super busy and I do appreciate everyone responding
94 C1500 5.7

@Schurkey
I would use the term released and not vacuumed, if the latter is required it would probably explain it. (too broke to get it done properly)
I didn't know what an orifice tube was, I'll be doing that soon when I have time seems simple enough. (and dryer since they're both inexpensive)
I'm not sure how many lbs of Freon was added, I just refilling with the cans, and it would show 40psi on the gauge, and still wouldn't kick on the compressor so I would just stop at that point.

@HotrodZ06
The cycling switch is the one in the compressor with a snap ring right? (if so, I replaced it already)

@Orpedcrow
I don't know for sure if the compressor failed at this point, It was new from the previous owner (I've owned the truck for less than a year) and initially I thought the clutch ceased on it but after pulling off the compressor and replacing it it seemed to move freely( with slight friction )
I'll try and buy the gauge set this weekend and see if I can give more information, after doing the orifice tube / dryer and see if its still ******

@scott2093
How would I go about testing the control unit? I have a multimeter to test the connections, just no idea what to look for on it ( I haven't taken it out or anything to see the back of it)
I did see a video where there was some burnt connections from the unit with wires going behind the glove box but that video showed the unit not even powering on so I'm not sure if that would be likely.

 

[Noobular]

Also my bad, This is the first time I've ever had to work on anything A/C related so i'm oblivious to mostly everything, just using videos on how to replace things.