A/C is blowing hot air

Car: Toyota, Corolla, 2003 - Back to Fix-It - Toyota Repair Manuals

Q.My air conditioner is blowing hot air. My wife was sitting in the car with the motor and air on last weekend. It was around 100 degrees and all of a sudden hot air started coming out. I had her to open the windows and turn off the motor and air. When I came back, I started down the road and tried the AC again. It started to cool and we had no more issues all week. I thought the line might had frooze up because it was a humid day. This weekend, it happened again except it still blows hot air even after sitting all night. Could this be a problem with the relay?

More Info required does the A/C Light flash when it starts blowing hot air?

Addition No, not that I noticed.

More Info required There are many possible causes for what you are describing so I am going to need to know a few more things. First, can you tell if the compressor is coming on and just not blowing cold, or is it not coming on? Second, need to know for sure about that a/c light.

Addition I just checked the AC light and it remains green. There are no check engine, etc. Lights. I will go check the compressor and let you know in about 5 minutes. Please send me another message so that I can reply. Thanks.

More Info required okay I will wait.

Addition To be honest, I am not totally sure. The belt to the compressor is turning. The RPM increases from around 900 RPM to about 1000 RPM but this could be due to the fan. I do not feel nor hear anything else kick in.

More Info required do you have a voltmeter?

Addition No, but I could go buy one.

More Info required Okay. Once you have a voltmeter, unpug the connector to the compressor and check to see if the wire going to the compressor has 12volts with the engine running and a/c turned on. Let me know what you find.

Answer There is no need to run out an purchase a meter yet.
Most likely if you have proper freeon levels then this is a relay issue as you originally questioned.
Open the fuse/relay block cover located under the hood behind the battery, remove the a/c magnetic clutch relay and the HORN relay, insert the horn relay in the clutch relay location and retest the system, if the a/c now works then you need the updated relay for this concern, no need to over analyze this if it's a simple issue.

Addition I switched the relays. The horn still worked and the AC did not.

Answer The a/c compressor is energized by this relay when commanded, if the a/c does not work then the a/c pressures need to be checked first, the pressure switch on the a/c line will cut out compressor relay power, keep this simple, if the compressor will not engage and the relay is not the issue then have the sysem pressures checked and recharged as needed next.

Addition OK. I will take it in have it checked out. If it is the compressor, do you know about how much one will cost. Don't worry, I will not hold you to it. I just want to get a general idea. Thanks.

Answer Compressors rarely fail on these cars. If this was the issue you can simply reach you hand down and turn the clutch that sticks out from the compressor pulley to verify that the compressor is not locked up.
Start with an easy/cheap evacuation and recharge for under $100 to start here. Other then some known issues with the relay failing the corolla a/c is very reliable unless the issue is damage related such as a rock from the road punctures the condenser and looses refrigerant level and pressure.

Addition Thanks! I will have it checked out.

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A/C is blowing hot air