I’ve had my 1991 F150 with the 5.0 for about 7 years and when I bought it the AC didnt work. It blows air just not cold at all. The compressor doesnt spin when the truck is running and AC on but I bypassed the low pressure switch and it started spinning. Pressing the schrader valve suggests it has no R-12. So yall think I should try finding R-12 to recharge it or just go with the conversion? I would hate to charge it with R-12 just to have a leak or another problem with the system that I don’t know about currently

 

Put some nitrogen and dye in it. Look for leaks.

 

You should already know it has a leak, it's empty.. A technician will use a sniffer to find the leak. . The leak needs to be addressed. With all the needed work ( repair the leak, replace the accumulator, evacuate the system with a vacuum pump, recharge the system) I would convert the system to 134A. It's not worth putting in R12 at this point. If you don't address the issues, you are just wasting time and money with it.

 

So would my current compressor work with the conversion or do I need to replace it as well

 

is it 34 years old?

 

How a pro like me does it
You can add 1 lb of R12 for testing and be ready to suck it back out with a recycler
Leak test with eyeballs first looking for any oily components like a big spot of oil on your condenser
Same with the hoses, that big hose going around the rear of the engine better not be oily, or the other small ones going to your condenser
Any oil on those hoses is a leak
I still fix cars using R12 and still have a bunch of it
I also retrofit them
No need to replace your compressor yet, unless you find that it is the leak
Retrofit is cheap and easy and will work just fine with your existing components
Might want to but a cheap China new compressor for 115 bucks or so
That way, you at least know the compressor shaft seal will be new and not leak
I buy about 20 compressors a year and just get them off Ebay
I get the cheapest Chinese one out there, located in the great USA
A retrofit kit will have ester oil in it.
If you retrofit, it
You need that ester oil to make the new PAG oil work with the residual old mineral oil in your old R12 system

 

to my knowledge its never been replaced…looks factory

 

So for me, either way staying R12 or switching, I would replace the compressor and any other necessary item like an accumulator/dryer if equipped before moving on. JMO

 

You can get a cheap new Chinese compressor for 110 bucks
I would replace it too for GP's if you have the dough
The system will probably work without one for now if you're broke

 

I had the same deal with my 91 2WD, non-working R12 system for a long time.

I bought on Rock Auto.....new reciever drier, new plastic tube "orifice" (Red I believe) for R134, all new flex lines, took apart/replaced all O-rings at connections underhood, bolted a rock-auto $110 compressor into place.

I installed all this stuff in a couple hours, went to my friends house with a HF Tools vacuum pump and drew the system down, added lube and freon....

VOILA! My 1991 F150 now has the COLDEST AC out of my fleet of 6 cars by a long shot!! Going on 3+ years now.

I encourage you to follow this path, not cheap out.....you'll be really happy with how your AC works.
Putting a price to it...I have under $400 into everything I described.