I drive a 2003 Mitsubishi Outlander. I bought it used about 4 years ago, and I have never had the A/C serviced because it always blows cold. I am good about keeping up with regular maintenance and repairs. I live in AZ, so it's hot here. And I mean, HOT. The other day while I was driving my AC blew warm for about 30 seconds when I was going up a hill on the freeway. The engine was working hard and I don't expect perfection, but I thought it was worth looking into.The AC blows cold at all other times, and was blowing hard and cold when I dropped it off for service. I took it to a mechanic that I trust and he said there was only 9 ounces of refrigerant when there should be 19. Obviously, we decided this was the problem and he had his son recharge it. As I was driving away, it started blowing warm. This has never happened to me apart from that one time on the freeway. I took it back and they realized that his son had made a math error, he had only recharged it with 13 ounces of refrigerant. That seemed 'off' to me if it was working with 9 ounces, but I let him try again. When the car was recharged with the full 19 ounces of refrigerant the AC performance was even worse. Hot air. They were gracious enough to do hours of troubleshooting for me. A small leak in the hose, and one lazy passenger side fan was the final diagnosis. My mechanic and I are both very analytical and so we decided to bring to refrigerant level back down to 9 ounces, just for kicks. IT WORKED. The AC blows cold at 9 ounces. What the heck? I do want to repair the hose and the fan, but is it even going to fix this problem? Have you ever heard of an AC only working with LESS refrigerant? My mechanic said he was completely stumped. He said he's never seen this in 30 years. Expansion valve is kicking ***, and there are no signs of damage in the compressor or the condenser. At 13 and 19 ounces of refrigerant, the pressure gauge responses were out of whack. The high pressure would go very high and the low pressure would go very low. AC would pump hot and engine would begin heating up. At only 9 ounces, pressure gauges and engine temperatures were normal. Any thoughts? They don't want me to damage the compressor, but they let me drive off with only 9 ounces since it was 120 degrees in AZ today. Yikes! Any ideas are appreciated.

 

wondering if they were not measuring correctly for some reason. refrigerant works best with a specific amount of refrigerant. too little, it won't work....too much, it won't work.

 

Exactly - too much refrigerant and the system will not work, good thing you found the leak though, it would cause trouble in the future. My guess is since it is a very hot environment you live in, the shop is not adjusting the calculations for ambient temperatures. Between 60 and 80 degrees, you can fudge the gauges a little and still have a working system, at 115 degrees, you need to majorly adjust your calculations - temperature = pressure when working with ac systems