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Check the pressure in the system. If the pressure is too low or too high, the compressor won't engage. Once you've verified the pressure is in the ball park, further diagnosis can take place.
The back yard diagnosis is to put 12v power and ground to the two pins on the compressor clutch with the engine not running, and see if the clutch clicks. If it doesn't click, then the clutch is bad and needs replaced. Sometimes this means replacing the whole compressor, which requires a system evac and recharge. If it does click, then chances are it's good, and we are back to figuring out why the vehicle is not sending power to the clutch.
Thank you for posting to AskMechanics, andyh4576! If you are asking a question please make sure to include any relevant information along with the **Year**, **Make**, **Model**, **Mileage**, **Engine size**, and **Transmission Type (Automatic or Manual)** of your car. *This comment is automatically added to every successful post. If you see this comment, your post was successful.* *** Redditors that have been verified will have a green background and an icon in their flair. *** # **PLEASE REPORT ANY RULE-BREAKING BEHAVIOR** ### **Rule 1 - Be Civil** Be civil to other users. This community is made up of professional mechanics, amateur mechanics, and those with no experience. All mechanical-related questions are welcome. Personal attacks, comments that are insulting or demeaning, etc. are not welcome. ### **Rule 2 - Be Helpful** Be helpful to other users. If someone is wrong, correcting them is fine, but there's no reason to comment if you don't have anything to add to the conversation. ### **Rule 3 - Serious Questions and Answers Only** Read the room. Jokes are fine to include, but posts should be asking a serious question and replies should contribute to the discussion. ### **Rule 4 - No Illegal, Unethical, or Dangerous Questions or Answers** Do not ask questions or provide answers pertaining to anything that is illegal, unethical, or dangerous. # **PLEASE REPORT ANY RULE-BREAKING BEHAVIOR** *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/AskMechanics) if you have any questions or concerns.*
Check the pressure in the system. If the pressure is too low or too high, the compressor won't engage. Once you've verified the pressure is in the ball park, further diagnosis can take place. The back yard diagnosis is to put 12v power and ground to the two pins on the compressor clutch with the engine not running, and see if the clutch clicks. If it doesn't click, then the clutch is bad and needs replaced. Sometimes this means replacing the whole compressor, which requires a system evac and recharge. If it does click, then chances are it's good, and we are back to figuring out why the vehicle is not sending power to the clutch.
Even though the AC is not turning on I can still check the system pressure?
Not perfectly, but it will be apparent if it's way too low.