Q: A/C blowing hot air

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My a/c just started to blow hot air, I was driving and it went from running cold to warm. I have checked the relay, but the clutch is not engaging and obviously the compressor is not running. My question is if the system has run completely out of refrigerant and tripped the low pressure safety switch or the switch is faulty, how can I get the compressor to kick on so I can get a reading on the freon pressure and possibly fill it if it is empty?

My car has 110000 miles.

A: Whether or not the freon is low, it can be ...

Whether or not the freon is low, it can be tested using a/c gauges. The a/c compressor doesn't need to be running to check system pressure, only to check operating system pressures. You can hook gauges up anytime and see what the resting pressure is, which is what the low pressure sensor is monitoring anyway. It is against the law to put Freon into a vehicle with a known leak except for testing only. If you have a leak it could be any number of components, such as the condenser in the front of the radiator or a high pressure line. If you want to check the system pressure you can usually get an aftermarket pressure gauge at a local parts store, though I strongly recommend having a certified mechanic diagnose the a/c issue, such as one from YourMechanic.

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