AC Expansion Valve Pipe temp... SLIGHTLY cold or VERY cold ?

[FishTail]

QUESTION: Should the AC expansion valve tube (where enters firewall) be SLIGHTLY cold or VERY cold to the touch ?CONCERN: AC not working, suspect Freon is fully charged. (at 35 psi)BACKGROUND INFO: My AC this year seems to be 95% dead. Compressor fly wheel spins and radiator fan turns on, but vent temp is only about 68 degrees, when outside is 75. Under the hood, tube from expansion valve is only slightly cooler than ambient right at firewall. Freon currently reads at 35 psi when running.Thanks for the help,FishTail(James: 2004 Vibe, 100k)

[engineertwin2]

Unfortunately, this isn't enough information for us to answer your question.When you say 35 psi, is that high side or low side pressure? Given that you referenced the temp at 75F, I would expect a static pressure around 75-80 psi, but again I don't know where you took the pressure reading from.Have you checked to make sure the HVAC recirc door is closing all the way?Specific to your question, the expansion valve should be pretty cold when the system is in operation. If it's not, you need more information on the system to determine if the valve is stuck open, stuck closed, or the system is under or over charged.

[FishTail]

EngineerTwin2,Good questions. In short; 35 psi on low side, while under full running load... To better explain; I assumed it was low on freon, and purchased a do-it-yourself freon kit. Following it's instructions I ran AC on full blast for about 5 minutes. Then used their gauge to check pressure BEFORE adding any. It read perfectly in the middle of their "fully charged" range. Based on their other model's of gauges, I'd estimate that as a 35 psi reading. I did NOT add any Freon.The compressor clutch spins when I turn on the AC. But I noticed that the freon line after the expansion valve (where enters firewall) is only slightly cooler than the return one. I drove for over an hour, and this was still the case. I'd ballpark the line temps at about low 60 going into the firewall, and maybe 70 coming back.I'm not very familiar with the mechanics of the car, but am very willing to learn if you can help. what should I check/do next? SUMMARY: =Air not cold (cools about 5 degree delta drop, only)=35 psi, on low side freon, while running under full load=Freon tube after expansion valve not getting very cold (maybe 8 degree delta drop, only)=Compressor clutch and radiator fan DO turn on, when AC is turned on=Radiator area appears undamaged, and fairly clean, clear airflow

[engineertwin2]

I'm concerned the expansion valve isn't working properly. It could be stuck...you may need a certified mechanic as the system should need to be drained to service or replace line components.Also, FYI, don't add Freon...I believe the system uses R134a. R113 (Freon) and R134a can not be combined in the same system.

[Daddio]

I just read the user manual's a/c charging instructions the other day, which said something like - charge it until the suction line gets cold.Wouldn't that be overcharged? ... and vary depending on the ambient temperature? I vapor charged my system the other [really hot] day by watching hi-side pressure, and I stopped when it was about 240-ish. The suction line was never really very cool. Now I suspect my tx valve as well. Are these expansion valves electronic? Might the sensor be out of place or damaged?D²

[djkeev]

It is truly scary hearing what people do themselves to something as potent as an air conditioning system. It is a high pressure gas and can cause significant injury to a person. There are special gauges and special procedures to follow for safety and proper operation. One of the most important things is the presence of air in the system. Before charging the system is evacuated to 29hg of vacuum, almost an absolute vacuum. Into this vacuum which contains no oxygen or moisture the coolant gas is introduced. Once you have a leak and gas leaks out, air and moisture leak in. This will over time not only stop the ac from being cold but cause problems with the receiver dryer, the inline filter, the compressor and any other part that can rust.IF you don't have the tools, pay someone to fix your system that has the tools, it is one of those jobs that 100% requires special tools, there is no way around this need. Accept the fact and go to a pro with the tools or go purchase the tools (about a $500 investment)and learn how to service the system. If you get a cooling gas recovery tank (as required by law) the cost of tools will be in the $1000's.Dave

[FishTail]

But if my system still has 35 psi pressure (on the low side while running) wouldn't it be just about impossible for ambient air/moisture to get in? (i.e. pressure leaks out, from 35psi to ambient, not in)Please explain.Thanks.FishTail

[tpollauf]

Quote, originally posted by FishTail »But if my system still has 35 psi pressure (on the low side while running) wouldn't it be just about impossible for ambient air/moisture to get in? (i.e. pressure leaks out, from 35psi to ambient, not in)Please explain.Thanks.FishTailAfter already replying to this similar problem in another post, here's what I'd do at this point ... AND unfortunately YOU do not have the tools or expertise to do it. It is very possible you no longer have PURE R134A in your system which would explain the lack of cooling. Somebody, prior to you, could have added what they thought was the proper refrigerant and mad things worse. You also possibly have "non condensables" AKA ... air, in your system which when mixed with refrigerants, forms acids You need to dump the current charge, evacuate the system down to 500 microns, then charge the car BY VOLUME (not weight, and NOT by pressure) so you get the exact charge required by the mfgr. Their should be a sticker under the hood stating what that volume is (28 oz. give or take). A charging cylinder works best where you can measure the volume of refrigerant entering a system. Go for it and let us know the results

[engineertwin2]

Quote, originally posted by tpollauf »...You also possibly have "non condensables" AKA ... air, in your system which when mixed with refrigerants, forms acids ...Minor correction for you:It is the constituents in the air that are non-condensable, such as nitrogen (N2), CO2, and hydrocarbons. Yes air is 80% non-condensable, but eir is a multi-constituent gas that is semi-condensable.

[FishTail]

tpollauf: My "FREON" is the proper one, I did not install the wrong one. In NY, they use this term to describe ANY refrigerant, not just the older ones. Even my mechanic's bill says "freon" on it, refering to the proper refrigerant for the Vibe.MY SOLUTION: I ended up taking it to 2 shops to fix my problem. The first shop charge me $70 to pump it with dye. They said I had a pair of BIG leaks, and a few smaller ones. Assuming they were honest, THAT MEANS THE DO-IT-YOURSELF GAUGES THAT SAID MY FREON WAS FILLED, WERE WRONG! And all this time my system was empty. That first shop wanted $500 to $1000 to fix "everything", which meant they would replace major components. The second shop I went to, said they could "repair" the defective schrader valves (replace few small parts in them) vs replace the full hi and low lines. They also placed a gasket in another leaky spot, and said there WERE NO OTHER leaks. This second shop, cost me only $200. Now, I'm cold and happy.