1994 A/c blowing out the expansion valve

[porreca1]

HI I bought a 1994 Ranger 3.0 4x4 for my kid's first car...nice truck only 100K on the clock...ex government truck used in some mines around here(Utah). The truck has been retro fitted to 134, it even looks like a factory job. The guy said it "just needed a charge" ...yeah right ... did that and it took the can, blew cold then started blowing out the expansion valve until gone and shut off by the low pressure switch. I assumed it was a clogged orifice, but reading here it is either orifice or expansion valve not both...any ideas? maybe a blocked drier? hate to start in replacing parts one by one without a good idea what it is...

 

[4x4junkie]

1994 was a transitional year, some trucks came with R-12, some with R-134a, so it could infact be factory.
In either case, it's an orifice-tube w/accumulator system and is controlled by a cycling switch (there is no expansion valve or drier). The desiccant is in the accumulator.

Where exactly was the system leaking from? If it's a fast leak, the system is probably contaminated (air, moisture, etc.) and would need to be evacuated before being charged with refrigerant.

 

[porreca1]

1994 was a transitional year, some trucks came with R-12, some with R-134a, so it could infact be factory.
In either case, it's an orifice-tube w/accumulator system and is controlled by a cycling switch (there is no expansion valve or drier). The desiccant is in the accumulator.

Where exactly was the system leaking from? If it's a fast leak, the system is probably contaminated (air, moisture, etc.) and would need to be evacuated before being charged with refrigerant.

Thanks for the reply ..The first photo is where the 132 is pushing out...looked like an expansion valve (it is on the back of the compress) ...who knows! The rest are just a few of the system...When I was done I checked for any pressure by unscrewing the low pressure switch and pushing on the schrader...nothing remains...pushed it all out...has to be blocked somewhere....

 

[kimcrwbr1]

I believe that is the high pressure relief valve does the tube connected to it go out to the condenser in front of the radiator. It could be a plugged orifice or strainer. You need a set of guages on it and then see what the pressures are doing if you getting real high liquid pressures and low vapor it is probably the orifice or a plugged strainer. By the way a orifice is a expansion device. when the high pressure liquid passes thru it it flashes off to a low pressure vapor. The vapor goes thru the evaporator in the cab and the vapor absorbs the heat (superheated vapor) that goes out to the compressor and turns it into a high pressure vapor. That goes thru the condenser and as the heat is pulled out of the vapor it condenses into a high pressure liquid (subcooled liquid) that goes thru the expansion device to flash back into a vapor and the cycle continues. Your not adding cool your removing the heat out of the cab. Can you tell I`m bored that is my A/C 101 lesson for today
If it does indeed have a TXV thermal expansion valve I believe the strainers are built into it?

 

[adsm08]

That is in fact the over-pressure blow off. Most of them are one-time use and never truly reseal.

The first order of business would be to inspect the orifice tube. See the double nut fitting int he third picture? Go find the OTHER one and unscrew it, pull the little screen out (the book says you need a "special tool", I have found needle nose pliers work really nicely) and take some good pics of in before you clean it off. Odds are good that you will need some major repairs to the system to make it work correctly.

If the orifice is, by some chance not plugged solid I would charge it up, and get some gauges on it. Most of those safety valves blow off above 400 PSI. The only ways I know to make that kind of pressure are to plug the orifice solid or kill all air flow across the condenser (the one in front of the radiator).

I would also recommend replacing the high-side cycling switch since that is supposed to shut the compressor down before it hits the blow-off pressure.


An expansion valve (also called an H-valve) is a form of variable orifice. It is a spring loaded variable valve that opens and closes to vary the rate that refrigerant passes into the evaporator. They are supposed to provide better overall AC performance, but that comes at the expense of the compressor running for longer periods of time and the loss of the filtering effect of a traditional orifice tube.

 

[porreca1]

That is in fact the over-pressure blow off. Most of them are one-time use and never truly reseal.

The first order of business would be to inspect the orifice tube. See the double nut fitting int he third picture? Go find the OTHER one and unscrew it, pull the little screen out (the book says you need a "special tool", I have found needle nose pliers work really nicely) and take some good pics of in before you clean it off. Odds are good that you will need some major repairs to the system to make it work correctly.

If the orifice is, by some chance not plugged solid I would charge it up, and get some gauges on it. Most of those safety valves blow off above 400 PSI. The only ways I know to make that kind of pressure are to plug the orifice solid or kill all air flow across the condenser (the one in front of the radiator).

I would also recommend replacing the high-side cycling switch since that is supposed to shut the compressor down before it hits the blow-off pressure.


An expansion valve (also called an H-valve) is a form of variable orifice. It is a spring loaded variable valve that opens and closes to vary the rate that refrigerant passes into the evaporator. They are supposed to provide better overall AC performance, but that comes at the expense of the compressor running for longer periods of time and the loss of the filtering effect of a traditional orifice tube.

I think you are talking about the fitting in the pic below...how the h do you get those apart with needle nose? I will try it...isn't it one of those you push together to pull apart....crazy Ford...Thanks for the input, it sounds like I will need a new pressure valve as well. I have a pro in the wings ready to help, however that will require me asking for help in person....you guys are just as good and less of a knock on my pride....

 

[adsm08]

No no no. The arrow points to a spring lock coupler. Not what I am talking about at all.

There should be another line going into the heater/evap box that also has two hex nuts but is not in that pic. The orifice should be in that fitting.

Postin' from teh Galaxy

 

[porreca1]

No no no. The arrow points to a spring lock coupler. Not what I am talking about at all.

There should be another line going into the heater/evap box that also has two hex nuts but is not in that pic. The orifice should be in that fitting.

Postin' from teh Galaxy

Got it...does not look too bad...now I am thinking that maybe the guy did not put a vac. on the system before filling....could cause the over pressure....I am out of other ideas...

side note spring lock couplers suck...disconnected that one too....

 

[porreca1]

another shot

 

[adsm08]

Id get some gauges on it and see what it does. You also have to be careful with those stupid cans you get at the parts store. You charge
Ac systems by weight, not by pressure. Those cans only go by pressute.

Postin' from teh Galaxy

 

[kimcrwbr1]

Just to be safe put it on a vacuum pump and evacuate it for at least three hours that will boil any water that may have mixed in the oil. If it went into a neg vacuum on the low side it is possible it pulled in ambient air with current humidity that equals water. A single drop of water can destroy the compressor from the acid it creates. Any time you open a system it pulls in moisture tape the ends of the fittings to keep from moisture intrusion. +1 on adding the refrigerant by weight, try and get as close to a factory charge as possible. any digital scale will work good weigh the can/s before and after adding the charge. If you can get a bottle of nitrogen and a regulator blast out the coils and lines good and then do a pressure test with nitrogen. put around 200 psi in and spray soapy water on all the fittings I test at 50 psi first low pressure gets better bubbles and the run the pressure up and wait 45 minutes. You want zero loss, the pressure will actually rise with higher outdoor temperatures. Pull it into a deep vac the longer the better at least 45 minutes then add the charge until the low pressure switch allows the compressor to turn on then pull the remainder in the low side until you add the factory charge by weight.

 

[4x4junkie]

Thanks for the reply ..The first photo is where the 132 is pushing out...looked like an expansion valve (it is on the back of the compress) ...who knows!

That is actually a low-side pressure relief valve. My Ranger had issues with that valve also (factory R-134a), so maybe this is a common issue (I'm not even sure what it's purpose is... the low side is never pressurized by the compressor, it's pressure actually drops during operation. My BII has no such valve at all on it's low side).

My issue was when running the engine in hot ambient temps with the A/C OFF (especially at high elevation), that valve would release the freon to the atmosphere (defective in that it's pressure point was set too low). Unfortunately it didn't become obvious this is what was happening until after the warranty ran out I noticed the A/C was no longer cooling as well.
While fixing/recharging the system I blocked it off entirely (leaving the high-side relief valve & cutout switch in place for obvious reasons). Since then I've not had any further issues with it.

My suggestion would be to do the same, replace the orifice tube with a new one (they're $10, replace it), replace the accumulator (new desiccant), replace all the o-rings in the stsyem, then button it up and do a full evacuation and recharge on it (22 oz R-134a and 7 oz PAG46 oil IIRC).
Your old orifice tube looks relatively free of debris, however watch out for presence of thick black sludge (Black Death) when you pull the lines off the compressor and condenser for your o-rings. Black Death = replacement of those latter two items is required as well (in addition to replacing the discharge line too if it's got one of those muffler thingies on it).

Hope that helps.

 

[adsm08]

Isn't black death usually caused by using the wrong refrigerant?

 

[4x4junkie]

It comes mostly from having insufficient oil/wrong type oil, and/or running it with contaminants in the system (certainly you could call a wrong refrigerant a "contaminant" though).

I think how it usually ends up happening is people continually pump cans of freon that have wonderful "stop-leak" chemicals and other gooeyness in them into a leaky system hoping maybe they'll eventually plug up the leak, but instead that crap ends up displacing the system's original lubricant leading to the compressor's death (plus any air/moisture that has entered through said leak would be contributing to it as well). Debris from the failed compressor then gets lodged in the condenser coil and line mufflers where it's basically impossible to fully remove it by flushing (and is why it's best to replace these parts when cases of Black Death occur).

 

[adsm08]

Yeah, I don't usually have to deal with black death issues since I find and fix the leaks, and at the first sign of compressor failure I start replacing stuff.

I just thought that I read somewhere that 134a when mixed with esther oil can not only gum up the system but eat at the rubber lines.