My 1985 SR5 has the following symptoms:

1) No signs of cool air out of the vents, stays at outside temperature
2) AC compressors kicks in and runs when the AC button is pressed, does not cycle, stays on. So I am believing there is some Freon in the system or the low pressure switch would stop the compressor clutch from engaging, and I should see some downward movement in vent temperature.
3) Light on the AC button is on
4) There are no air bubbles in the dryer inspection port during running or after shutting the system off. There is fluid in the port.
5) System is still with R12

I have ordered adapter hoses to connect my R134a gauges to the R12 system, so I can see the pressures on both sides.

Any ideas of where to go next?

Thanks

 

Convert, evac, pressure tested and go from there, won’t really know until it’s all tested

Did it just stop working or has it been this way for a while?

 

It stopped working several years ago while I was overseas, so I don't know if it was gradual or a sudden nose dive. It's just the next project to tackle.

Another point to mention is: One hose to the compressor is hot and the other noticeably less hot, which to my understanding is the way it should be, if the compressor is working.

 

Hot hose is the high pressure/discharge side. Cold/not hot side is the low pressure/suction side. Gasses get hot when compressed. Think of your garage air compressor tank getting warm during use, or the entire concept behind how a Diesel engine works.

You'll need to locate the leak. It is possible that there isn't a gross leak and the freon slowly leached though the rubber hoses. This is totally normal over time to lose some refrigerant at a very small and acceptable rate.

Sometimes you can see the leak due to a bit of oily wetness around a joint. Unfortunately this is hard if the leak was super small or everything is already covered in grease. This is very possible on a 30+ year old truck. Also, there are connections in the dash which you cannot inspect without disassembly.

You should have the remaining refrigerant evacuated by an A/C professional to avoid releasing it into the atmosphere. R12 capable shops are getting very hard to find. Simply not a lot of money in it for them anymore.

R12 works best hands down. But it's a little harder to find, more expensive, and it's very bad for the environment when it eventually leaks out. There are theories that every bit of R12 ever produced will eventually be released into the atmosphere either through leaks, accidents, or neglect. Converting the system to R-134a is probably the right thing to do, but is expensive to do properly. You'll probably have to get a larger, universal fit, parallel flow condenser to have acceptable performance.

 

Did you visually see the compressor kick on and off?

There is a low pressure switch inside the evaporator under the dash. It might be bad. You can check by removing the glove box and pulling the plug. Check continuity on it. If it is open that means that you have low pressure or the switch failed. Make sure you have the right plug because these is also a thermistor.

Also, there is an expansion valve down there. That might be bad as well.

Do you have acess to an FSM? If not I would google serach one in PDF. It has a really good portion on the A/C system. That is how I diagnosed and troubleshot mine. .

 

Yes, most likely low on refrigerant.
Same symptoms on mine. It worked almost perfectly for 6 years, until I left it un-operated for 3 months to go there. ...
I looked it over and I did not see any sign of refrigerant leak. Theory is slow leak like above^^^ because of shrunken seals from non-operation, etc.
I also got hit with a more urgent issue (overcharging) so had to work on that.
Local O-Reilly does not have loaner gage so to quickly troubleshoot (not ideal but practical), I got refrigerant in can, gage on low side said low. Refilled it with one can. Now it works very well.
Nest steps:
1) Find legit manifold gage,
2) Find good tank of refrigerant and top off,
3 Monitor