i guess it could break down molecularly to a point the gas is no longer sufficient enough to produce cold air?? However its likely your lines may have a bad seal somewhere. I good purge and refill usually do the trick i think provided you don't have any leaks in the system .
Also if the A/C system has ever been openned to service the engine... meaning they had to open the lines or remove the A/c compressure to do engine work or what ever its usually a good idea to replace the evaporator. _ mil
It can also be a clog in the restriction that breaks down the high pressure gas to the low pressure gas. I think Scuba2001 had a post on this a little while ago. If the restriction does not let enough gas pass into the evap, then the cooling in the car is not up to capacity.
Refrigerent doesnt "breakdown" as its in a constant gas/liquid state all the time. As the gas passes theough the compressor, its a high pressure gas. It then passes through the condensor (part thats in front of your radiator) and cools to a high pressure liquid. It will then pass through your restriction (in our case, orifice tube) and will then become a low pressure liquid. As it passes through the evaperator (located in the passenger compartment), the low pressure liquid becomes a low pressure gas. The evaperator works by sending air through the fins and will heat the liquid up, and cause it to boil. It will then pass through the accumulator (reciever/drier) which will remove any moisture out of the refridgerant. Then, it will pass back into the compressor which will super heat the gas back into a high pressure gas, and the system starts all over again.
The AC system is injected with a yello dye. Under a UV light and special glasses, this dye will florese and will be a bright yellow color. Use this light around any fittings, housings, hoses, condenser, evaporater drain tube, etc. If you see this stuff light up, you have a leak. Remove all refridgerant and replace any fittings, hoses, o rings, etc with all new parts.
As I JUST went through an automotive AC class at school, this stuff is still fresh in my mind. And with my experience, I was having the same issue as you where the car wouldnt cool. My class worked on my car, and got it all back up and running. We found that the restriction device (orifice tube) was coaked with oil, metal shavings, and debris from the compressor. With this, its the beginning of what the AC world calls "Black Death." If let alone for too long, the stuff will basicly tear your whole AC system to parts and will blow oil and other "black death" debris into the passenger compartment of the car.
Sounds good to me. Just make sure you buy the right parts and have a reputible shop do the work. AC work isnt something to play around with for a DIY job. BTW... the restriction/orifice tube is actually the same size as a basic run of the mill tube. You should just be able to get one from AutoZone I would think.
I didnt have to worry though because we had about 1000 of them in a bag, all the same size, etc. at school.
Scuba's got it, the refrigerant gas doesn't break down or get old. If air or water gets in the system, however, the pressures may read correctly but the system won't cool because the refrigerant won't vaporize in the evaporator. Expired dessicant in a system (which can happen as it gets 'old') can faiil to absorb water and lead to this condition. 2 more cents on the fire...
Reciever/drier... What year is your car? Most reputible shops replace them anytime that the ac system is opened and if you have a leak somewhere, it would be best to replace it. Its a can like aluminum part that has 2 hoses ( one in, one out) and then usually a fitting for the pressure sensor. Will be located under the airbox on the passenger side, next to the ac compressor. If all you are replacing the orifice tube, I think you should be fine with not having to replace it. Its all up to you though. The system would probably work better with a new drier on it.
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