A/C too cold...

[sly]

the OE sensor has an adjustment screw in it. I have no clue which way adjusts it up or down, but that's also where it usually leaks from when it goes bad in my experience (which is why adjusting that voids the warranty on new ones - or so goes my theory). It might be worth a shot to get it to cut out at a higher pressure, but you would need a low-side gauge to figure that out... adjust it half a turn and see where it changes to from before the adjustment... then adjust to the desired level (probably 15-20 PSI).

[andrew_mccaffrey]

will the R134a fittings screw on to the little coleman propane bottles? if not, how do you connect and fill your system?

[OilBurner]

134a uses special (synthetic) oil and is not compatible with R12 or propane. To convert an r12 system to 134a properly, it needs to be totally flushed out, all the oil changed and all old refrigerant removed. Many DIY kits have little/no info about this and if its just added in or even only evacuated and not flushed/cleaned it will still mix with the existing older refrigerant and possibly damage the compressor...this could be why it ate 2 compressors, to whoever said that. unless they were junkyard compressors anyway.

Propane and actual R12 both work with mineral oil (there are also r12-safe compatible synth oils out there...theres 2 major types used with 134a, only one is r12-safe and i forget which one that is) and mix together fine, so you can just add R290/propane to an R12 system and it should be fine.

It was my understanding that the pressure cut off switches, both high and low, are only there to protect the system from damaging itself...the low switch cuts it off if theres not enough refrigerant in the system, the high cuts it off if there is a clog in the evaporator or something else that causes very high pressure to build to prevent pipes from rupturing or the compressor damaging/bending its internal valves or blowing seals apart etc..

The cabin/evaperator temp should be controlled by a temp sensor...not by the low side pressure...as even if everything is properly working it will still result in the evap icing up if its humid and the car being frozen...i think this is just poor design on Fords part if they engineered it without a temp controlled switch...its also inefficient to run the compressor all the time and use the heat to compensate if its too cold...so i think it would make perfect sense to add one it...which could be done using a simple 120v mechanical line thermostat meant for A/C or a fan from home depot or something...and wire it so it just turns the compressor off once the cabin reaches 60*...or whatever is preferred...this im sure could be gracefully hidden under the dash somewhere.

there is a small fitting available meant for camp stoves that screws directly into a coleman tank that has a screw fitting on the other side...i think i got mine at tractor supply. Look around the internet. I put a small ball valve after this tank adapter and then a barb fitting which i just camped a refrigerant hose that i cut the end off of to, and then that hose goes up to a manifold gauge set as normal. This is what you want: https://www.flameengineering.com/fil...roduct_151.jpg

[gadget73]

ester oil is the conversion one. It works with R12 and R134a. PAG is the 134a-only oil in native systems.


The low pressure switch does 2 things. One it keeps the compressor from running if the system is dry. The other thing it does is prevent the evaporator from freezing up. If you look at temperature to pressure curves for refrigerants, you'll see that as the pressure drops, they get colder.



as an example. You can also see why you have to tweak the pressure switch downward a bit for r134a to help with performance. It has to run lower pressure to get to the same temperatures. Make the evaporator too cold, and the moisture in the air just freezes to it, turning it into a big block of ice. The balance is getting it as cold as possible without making it so cold that water freezes before it drains out of the fins.

The pressures with propane appear to be higher for the same temperatures:



The stock R12 cutout is right about 25 psi if memory serves. R134a is usually set to 20 psi. Based on that, I'm guessing you'll need closer to 50 psi with the propane to keep it from freezing.

There is no high pressure switch. That showed up in the 90s with round cars.


and believe me when I tell you there is no interior temperature switch. Its a fixed orifice / clutch cycling system. Its cheap, primitive, but reliable. Not efficient at all, but that wasn't their goal.