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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 realised 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. The expansion valve is kicking ass, and there are no signs of damage to the compressor or the condenser.

At 13 and then again at 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.

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    may be a faulty pressure switch/sensor over reading and opening the clutch circuit.
    – Ben
    Commented Jun 21, 2017 at 17:06
  • That vehicle has a very complicated AC system, you need to take it to dealer for a diagnosis.
    – Moab
    Commented Jun 21, 2017 at 23:36
  • Thanks Moab. Sounds like I should, appreciate the comment
    – Bethany Trapp
    Commented Jun 22, 2017 at 6:34

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If your freon pressure is too high, the compressor has a hard time compressing the gas. It's possible that you or the mechanic THOUGHT you were bringing the pressure up to 19 but really you made it higher; pressure gauges on freon cans have been quite unreliable in my experience.

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  • Could that point to a compressor or clutch fault where it's unable to work at the pressure required?
    – GdD
    Commented Jun 21, 2017 at 12:39
  • Thank you Iamax. To clarify, this was not a freon can. The refrigerant was vacuumed out and then added again by the machines used at the auto repair shop.
    – Bethany Trapp
    Commented Jun 21, 2017 at 14:31
  • Pressure on the gauge is not the same as a 19oz charge of freon.
    – Moab
    Commented Jun 21, 2017 at 23:48

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