AC Not Blowing Cold

[Jonathan Nicoli]

I have a 2011 Mercury Milan, the A/C worked fine a couple years ago but suddenly stopped working. The compressor will not come on by itself (car not letting it) so I jumped it at the relay and the clutch engaged and started running. However there still wasn’t any cold air with the A/C on full blast with the compressor jumped. I checked the freon, had it evacuated and recharged correctly (no cost to me), no leaks were found, and it still wouldn’t cool. The lines also weren’t sweating and were still hot to the touch. I noticed the cooling fan also wasn’t on and failed to jump so I’m having that replaced. Is there something else I should check for? I figure the compressor is worn out because when it cranks on it’s a little noisy, and I have yet to check the expansion valve for clogging.

Topic

[Keith Kachelhofer]

A set of HVAC gauges would help you diagnose the problem. You may want to see if you can borrow a set of gauges or purchase an inexpensive set of gauges from Amazon. The low side pressure and high side pressure readings will be dependent on the ambient temperature outside. IF the compressor is functioning properly then, assuming outside temperature of 90F, the low side should be around 45-55 psi and the high side around 250-270 psi. IF the A/C compressor is running and both sides read the same pressure then this would indicate the compressor is not functioning.

Also, be sure you have pulled a good vacuum on the A/C system before you attempt to charge. There can be no air in the system. Vacuum needs to be pulled on the system for a minimum 30-45 minutes to be sure you have pulled out all of the air and water. Yes, there is some moisture in the air stream. I have a separate vacuum gauge that reads in microns. The maximum vacuum reading on the system should be 500 microns. The system should hold vacuum for about 15 minutes with no movement on the gauges.

IF you have not pulled a vacuum on the system and given the age of the car, I would consider replacing the desiccant dryer as well.

IF all of the above has been met then, the outcoming air temperature on the center dash vents should be around 38F-45F with the car in motion around 60 mph. Be sure the A/C is on recirculation and the fan speed is around medium, not full blast. Be advised that the air temperature out of the vents will be dependent on the temperature outside and if the car is in motion. The hotter the temperature outside, the warmer the air out of the register. You can assume 50F-52F with an ambient temperature of 90F outside stopped in traffic. If stopped in traffic the outside air will be slightly warmer. Be sure to drive the car for about 15 minutes to get the A/C system time to circulate.

With the heat wave this week, A/C would be great.

[Author]

Replies