Air Conditioning Receiver/Drier

[03AP1]

Hey everyone,

Topic

[Marc Robertson]

If the system wasn’t properly vacuumed after it was opened and before it was recharged, the refrigerant may be contaminated with air on top of moisture. The same thing applies to the manifold set, if you open it to add oil or dye as this will also introduce air into the system.

A small amount of air won’t change the performance much if any but a lot of it will. It basically holds the place of the refrigerant yet contributes no refrigeration action. Air can be hard to diagnose on expansion valve systems such as the Civic. With a simple orifice system that is charged to the proper pressures, the refrigerant flow will be discontinuous between vapor and liquid when it should be continuous liquid.

Both moisture and contaminated refrigerant will be fixed by properly recovering the refrigerant, vacuuming the system and recharging . The receiver/drier should be replaced after the system is fixed. For the purpose of diagnosis, a good long vacuum will be enough but not enough for the long term. You cant recharge the desiccant because it usually require heat to release the moisture and not just a vacuum. Heat will probably damage the filter element inside. If the refrigerant is contaminated, it can give bad diagnosis readings. With this potential thorn in diagnosing the system, it may be best to have the refrigerant tested for air and other contamination or have the system recovered then vacuum and recharge the system with good refrigerant. Then re-diagnose the system for other issues.

With a manifold, you should be able to see other issues such as a low high side and a high low side pressure indicates either a worn compressor or a stuck open expansion valve. A high, high side pressure and a low, low side pressure indicates a blocked orifice or stuck closed expansion valve.

The tricky thing about diagnosing with the pressures is that it is very dependent on the ambient temperature, airflow past the condenser and the load placed on the evaporator. The load is the airflow and temperature change of the air through the evaporator. The load can range from a few hundred watts with a low fan setting on a cold day to the system’s maximum output which can be 10k+ watts on a hot day with the fan on high. The high side pressure is proportional to the heat load on the evaporator. Very high demand will put a high pressure on the high side. The other factor that determines the high side pressure is the condenser’s ability to remove the heat. This is because the refrigerant condenses as the temperature drops. Condensed refrigerant has a smaller volume than vapor which tends to lower the pressure when condensing.

If the expansion valve is stuck in the middle, it will act like it is stuck open for light loads and then act like it is stuck closed for heavy loads.

A thermostatic expansion valve is what the 2004 Civic has. It has the valve on the inlet to the evaporator and connects to a “bulb” located on the evaporator’s outlet with a thin tube. These valves are designed to maintain a specific amount of superheat, It is 7.5 degrees for the civic. The jargon superheat simply means temperature above the pressure/temperature chart for r134a. This ensures that there is no liquid present in the line on the way back to the compressor. A pressure temperature chart for 134a is located in the link.
http://autoforums.carjunky.com/Automoti … 4a_P59651/

The way to diagnose this valve is to measure the temperature of the outlet of the evaporator for a properly charged system. This won’t work if there is much air/moisture in the system or the charge isn’t correct. Use a moderate load such as the fan on low to medium. Then measure the pressure on the low side. In the pressure temperature chart, find your pressure and look up the associated temperature. The temperature of the line near the bulb on the evaporator’s outlet should be about 7.5 degrees above the temperature in the pressure temperature chart. If it is not correct, then there is either a bad valve or another issue preventing the expansion valve from being useful. An example of the valve unable to be useful is an undercharged system. The valve can’t do anything if it’s wide open and there isn’t enough refrigerant to properly condense. If the thermometer is in question, test it against a cup of ice water.

[EricTheCarGuy]

Excellent post Marc.

I hope that provides some insight into AC diagnosis, it’s never ‘cut and dried’ in my experience and personally I had to work in the field for a couple of years to get a real grasp on system diagnosis as there are SEVERAL things that come into play and to be honest I would suggest you take it somewhere to at the very least be diagnosed as if you don’t service the system properly you could cause enough damage to warrant the replacement of the entire system. In my opinion AC work should be left to the professionals, sure you might get lucky but you could also be very unlucky and it will end up costing you way more in the long run.

[03AP1]

Thanks Marc. I am going to test the expansion valve as you said. If it test ok I am going to go ahead and do what I said. I wont lose much, just about $100 including a new OEM condenser. and I am fairly confident I will not mess nothing up Eric, but thanks for the concern. I have vaccumed down and recharged a few cars already with great success. Diagnosing on the other hand is not as easy.

[03AP1]

Just a little update.

I found my a/c works pretty much 100% with the recerculation button on. (had to turn my fan down as it was getting too cold-Mind you today was over 90*)

Anyone can give me any tips. Since it was over 90* today in NY with the a/c on without recerculation it was borderline warm, but still partly cold.

Anyone here want to see the reading on my gauges?

Should I have a/c on low or high (Fan) when I connect my gauges?

Doors open or closed?

Thanks everyone

[Jeff Reynolds]

rice400 – I hope this applies to someone else 🙂 My 05 F150 cools great on highway but not so good idling. I replaced orifice, evacuated system, and charged with 34 ozs of refrigerant as Ford specifies on label. Still only cool at idle.

It was 93 degrees and pressures were 36 / 256. Lo side seems a bit lo. Pressure temperature chart shows lo should be 45 – 55 and hi 250 – 270. What can make lo side run a lower pressure while hi side in normal range?

[Author]

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