2010 Escape AC not cold. Edited version to explain the theory better.

Those pressures should look a little confusing, but they tell quite a story about the condition of the AC system in my Escape and why it isn’t cooling. The static pressures should closely match ambient temperature when everything has gotten to sit and cool off so that it’s somewhere between 60f and 85f. If the under hood temperatures are high than that will push the refrigerant pressures higher as well. But that high side pressure is too high, in fact after sitting for only a few minutes the two sides should have equalized, yet this sat for about an hour and the pressures were almost 100 PSI different.

One test that needed to be run is use a refrigerant identifier, this should be done on every job because you never know what has happened to a system prior to you looking at it. When the system is fully charged some of the refrigerant in it will be in a gaseous state and some of it will be liquid. When the compressor is running, the pressurization of the refrigerant concentrates the heat that it possesses on the high side , and that allows the condenser to dissipate that heat and allow the refrigerant to condense into a liquid.  By taking advantage of the latent heat of vaporization, the refrigerant actually releases more heat than just the pressure change would suggest. From there the refrigerant travels to the expansion valve or orifice tube. As the refrigerant passes through the orifice tube or expansion valve  the drop in pressure causes the liquid to boil and it absorbs heat from the air passing over the evaporator as it turns into a vapor.

There are a lot of things that can contaminate the refrigerant don’t condense into a liquid under the pressures and temperatures that an automotive AC system operates and the result lf them being in the system is typically higher than expected pressures, and very poor cooling. With my Escape  the static pressures are high, but that’s a function of the under hood temperature.

The next thing to do was to start the engine and see what the system did. The high side stayed at 210 psi, while the low side pressure dropped to 30psi and stayed there. Those would be normal pressures except the evaporator outlet tube  temperature was 78f, and that’s way too high.  That surface temperature means that there was no liquid refrigerant left to evaporate and absorb heat. Most techs would expect that with a high side of 210psi , and a low side of 30psi the system should be nice and cold, so why wasn’t it? Is this related to the high side static pressure being much higher than the low side at rest?

The answer to this one is that the expansion valve is sticking, or plugged up with debris sealing it off and reducing, if not completely blocking refrigerant flow. Now if you thinking about this, shouldn’t the compressor pump all of the refrigerant to the high side and pull the low side into a vacuum? It would except for the fact that it’s a variable displacement compressor that regulates the low side at 30PSI, so it simply stops pumping when the low side pressure reaches that pressure. The repair will include a new expansion valve and a receiver drier assembly. I’ll upload some pics of the repair if possible over the next couple of days.