1992 Mustang 5.0-System was R12, so I'm converting to 134. I vacuumed the systems and filled with 134. The compressor will cycle for a second or two, so I'm assuming maybe its good? It's only blowing hot air in the car and my friend helping says the 134 is not flowing through the systems. Before I just started throwing money at it, I thought maybe I would check with the experts and get some insight. Any thoughts on where I should start? Accumulator, Orifice Tube, or any thing I could check on the car? TIA

 

Converting from R12 to R134 is not that easy.

Besides the obvious high/low side valve size differences,
- You need a new compressor (R134 runs at a higher pressure than R12 and the seals are not cross compatible) SO, even if it works for a bit, it will blow out the seals on the compressor.
- ALL of the o-rings need in the system need to be replaced or you will get a leak.
- You also need to replace the receiver drier and flush (not just vacuum) the AC System. R12 uses mineral oil for lubricant. R134 uses PAG (a synthetic oil) for lubricant. They are not compatible with each other and R134 will not carry the oil to where it's needed so you will end up burning up your compressor even if it does fire up and that's if a leak doesn't happen first from the wrong o-rings or wrong oil.

Start over.

 

For what its worth,when I converted years ago,I didnt experience any problems after the swap.I also didn't replace anything in the ac system other than the new quick connect fittings that screw onto the existing fittings,which allows a set of gauges w/ quick connect fittings or a gauge/hose assembly w/ a quick connect fitting,to be used.Since the refrigerant and oil was evacuated from the system, meaning its bone dry,I would make a short jumper wire,disconnect the harness from the ac clutch cycling switch,start the engine and turn the ac/fan to max.Insert the jumper wire into the switch harness plug terminals and the compressor should come on.Open the valve on the gauge/hose assembly to allow refrigerant to be drawn into the system.When the can gets low on refrigerant, turn it upside down and shake it until its empty.Once the can is empty,remove the jumper wire and reconnect the harness to see if the compressor will come on & remain on.If it does,leave the harness connected and continue adding refrigerant until its full.If it doesn't, reinsert the jumper wire and continue adding refrigerant until its full.If the cans of refrigerant have oil in them already,the system should be full once 2-3 cans of refrigerant is added.If the refrigerant doesn't have oil in it,youll have to add it seperately.

 

You DO NOT NEED A NEW COMPRESSOR, nor receiver dryer to convert to 134a in a foxbody………if all r-12 is out.....put on the 134a conversion fittings, if you need to add oil if any components were changed add ESTER oil then pull system into a vaccum and leak test then charge to 80% of the r-12 charge using 134a...……..I have converted multiple foxes to 134a and never an issue using the above method...…….you could change seals but I rarely do as ester oil is compatible with 134a and r-12 oil......if your a/c is not working right after the conversion, you need to have a set of manifold gauges hooked up and see what the pressures are on the low and high side.

 

Good to know about the compressor on these (that's not the case for other vehicles) but the receiver/dryer should always be changed when you open the A/C system for work. That is basic, especially considering since any exposure of the open tubes to air allowed the desiccant to suck up ambient moisture plus, who knows the age of it. For all that is known at this point the desiccant sack could've opened in it and now the entire system has the black death.

Ester oil is synthetic like PAG and can be used if you're not draining out the old R-12 oil. Thank you for pointing that out.

Regardless, the problem now is, where did he go wrong? It could be the install, it could be the refill method, it could be a simple unrelated low pressure switch which would not be his fault. I've always been one to start from scratch on conversions and such so I can rule out certain bits of uncertainty.

OP, your helper is correct that the refrigerant is not flowing through the system. That's what the compressor does (pushes the refrigerant through the system).

What do the manifold gauges say when you fire up the A/C? If they don't change much or at all, it could be insufficient R-134A in the system or a defective low/-pressure switch. It's typically located on the Receiver drier. If the A/C kicks on, when you shut off the car, your high/low sides should equilibrate fairly quickly <1 minute during warmer temps. If the pressures don't equiplibrate or the process is really slow, a clogged orifice tube is possible.

 

WBROCKSTAR,MJR46,DERF00-Thanks for your replies. The help/comments are appreciated. My 89 GT went smooth years ago when I converted the AC. Just added the 134 with no problems, but this 92 LX did not. I do have another pressure switch, so I can check the switch and make sure its functioning properly. It may be the weekend before I can check when the pressure gauges. Any steps/advice on moving forward ? What should I read on the gauges and if it reads this check that? If I remember when we were filling with 134 it read high pressure on the low side.