So, was the switch hand tight? If it was that loose, you more than likely do not have any pressure in the system.

I’ll quickly press the low side with a rag over it. And yea it was hand tight
It took a bit of effort to tighten it but I could still move it without a tool

Well, that is a pressure switch, so doubtfully have any pressure in the system.

You can get a fairly decent set of gauges at HF and a vacuum pump as well.
But you need to get the system completely cleaned out first.

sandymane - okie dokie :-X22 I just wasn’t sure.

To the OP:

Based on everything I’ve read up to now, the system hasn’t been functional for some time. It’s likely there’s more than one leak to track down, so if it were my truck, here’s what I would do.

[The methods you use are at your discretion - I’m lucky enough to have access to professional grade equipment.]

1) Recover whatever amount of refrigerant is in the system.

2) Remove the orifice tube for inspection. Any signs of “the Black Death” or metal particles (which will ONLY come from the compressor), replace everything I can. If the lines prove difficult to source, then I’d be very thoroughly cleaning them out - even using bore brushes if I could.

3) If the OT is relatively clean, I’d flush the system as thoroughly as possible. Where possible I leave the lines connected and flush them at the same time as the evap/condenser. (But don’t attempt to flush the compressor.)

4) Remove the compressor and drain as much oil from it as possible into a clean container. Inspect it for excessive or large metal particles - reuse or replace as needed.

5) Clean any connections that were opened and Replace any seals. Lubricate o-rings with AC oil of the same type used in the system.

6) Add the necessary amount of oil (and leak detection dye) and vacuum the system for at least 10 minutes prior to leak checking and minimum 30 minutes before charging.

7) Charge the system with 1/4 the system capacity. This puts enough pressure in the system that any leaks that won’t hold static pressure to be located. If any are found, repair and retest. If not, proceed with enough of a charge to engage the compressor (60-70 % of system capacity).

8) Let the AC run for 10-15 minutes and inspect for leaks. If none are found, run the AC for a few days and recheck.

Given the presence of the adapter port on only the low side I would assume it has a mix of R-12 and R134a (if there’s significant pressure) and do your best to have it recovered by a shop. However I’d recommend you tell them you want it recovered because you are doing other work and need to remove the components. If they question you about the missing adapter on the high side, shrug your shoulders, because obviously you don’t know the history of the truck well enough to explain it anyway.

Sounds like a pretty good plan.

I pressed on the low side. It made a hiss and it got weak didn’t last 5 seconds. What tools would I need to recover the system and flush it myself? If I can do that myself, I can either buy r12 or take it to a shop to fill it with 134a. And I know I’ve asked this before, but I got many answers. What is everything that needs replaced to convert it? I know it needs different oil, but I’m more worried about do I need a new compressor, dryer, condenser, etc?

If it only hissed for a few seconds, the system is essentially empty - the hiss was likely due to residual refrigerant trapped in the accumulator.

To convert the primary things to do are replace the accumulator and flush the system.

Flushing chemicals are available at any auto parts store. You’ll need compressed air to flush properly.

IMO you’re better off with a “better safe than sorry” attitude and replacing the compressor anyway.

If you want to chance it, Pull and inspect the orifice tube to determine if the compressor needs replacement. If there’s excessive metal particles on it, I’d recommend replacing the compressor and condenser.

If there’s no indication of compressor issues, drain the oil from the compressor, add new oil and manually rotate the compressor a few times and drain it again to help clean the old oil out. Put at least 3 oz oil in the compressor before installation.

Add at least 1 oz oil to the evaporator and condenser, then put the rest in the accumulator.

A vacuum pump and gauge set is available at tool stores like Harbor Freight and Northern Tool.

After pulling the system into a complete vacuum, perform a leak check by letting it sit for at least 5 minutes. Any loss of vacuum greater than 2 in-Hg indicates a leak.

Typically 10 minutes will vacuum the system well enough for a leak test, but make sure to vacuum for at least 30 minutes total before charging.

Use R134a and charge to 75% of original R12 capacity.