Did someone work on the car recently? Did you just buy it? Air in the system can only get hot from the under-hood heat of the engine, otherwise it is going to be the same temperature as the air around you.
What is more likely is the system is just real low due to a leak. If you are expecting to see real cold gas spray out from the valve, that occurs because liquid refrigerant is rapidly turning into a vapor. That evaporation is what makes refrigerant do its thing. It becomes cold when it turns to a vapor and it gets real hot when forced from a vapor back to a liquid by pumping it into high pressure. If the system is low enough, there wont be any liquid left in it, only vapor, but it can still be under pressure. Refrigerant has an unusual property that when the system is at rest, and most importantly, there is enough in the system that some of it is liquid and some is vapor, the pressure will be almost identical to the surrounding air temperature in degrees Fahrenheit. In other words, if the air around you is 75 degrees F, the pressure in the system will be 75 psi.
If you were to bleed off some of the pressure, and lets say it dropped to 70 pounds, some of the liquid would vaporize and expand, and the pressure would go right back up to seventy five pounds. You will keep on reading seventy five pounds, no matter how much you bleed off, until all the refrigerant has vaporized, then the pressure will drop as you bleed more off.
Any liquid refrigerant in the system is going to be not close to the low-side port. That is because during charging, we want a vapor to go into the low side. Liquid would lock up and or damage the compressor. That liquid still in a system that is low will be in the evaporator in the dash. When you are bleeding off a vapor at the low-side port, liquid could be vaporizing a long way away, and it can warm up by the time it gets to the port.
To prove my story, bleed off a little from either port while holding the probe of an electronic leak detector by it. It will indicate it has detected refrigerant if that is what is blowing out.
I have to add that refrigerant is extremely dangerous to work with. It can cause frostbite and blindness. Professionals wear gloves and safety glasses, and the smart ones wear a face shield.
Wednesday, July 27th, 2016 AT 10:06 PM