QuestionLast summer my AC worked fine this last week I turned it on only to be shown this message "AC refrigerant very low AC compressor off " So I had a shop buddy of mine attempt to recharge the system but to no avail the compressor won't turn on " WHAT DO I NEED TO DO "
AnswerDid your buddy charge it by weight as a liquid or by vapor?
If he charged it as a vapor without the compressor running there is a good chance that there is not enough refrigerant in the system to close the low pressure switch.
But before I get into the checks, if it worked last year, and you have a low charge this year, it goes without saying that you definately have a leak that needs to be identified and fixed. Continued recharging is often more expensive over time than repairing the leak.
Ok, with your vehicle and A/C on. (Engine running or just switch in run position with engine off)Locate your compressor. Check your hot wire coming into it. You should have 12-14volts there at the connection. Preferably check this with a voltmeter, but if you do not have one, you can run a jumper wire straight from the battery positive terminal to the hot wire. If you do read voltage or run a hot wire and your compressor clutch does not engage... check your compressor ground. You may have corrosion built up around the ground connection that is not letting it complete the circuit.
If you do not read 12-14 volts at the compressor (regardless of whether or not the hot wire engaged the compressor) you need to locate your low pressure switch. Typically the low pressure switch is located on the accumulator, an aluminum "can" about the same girth as a soda can but stands a bit taller and has two lines coming out of the top. If your switch is not on the accumulator, trace your low side refrigerant line from the compressor until you find it. It may be connected directly off of one of your lines. When you find it do a continuity check across it. You should read resistance or hear a "beep" from your multimeter, because this switch is normally in the closed position. When the compressor pulls your low side pressure too low it disconnects and cuts power to your compressor, protecting it. A quick check for this switch, if you do not have a multimeter, is to... disconnect the switch and with and insulated wire, jump the terminals of the wiring harness plug. You should hear the compressor clutch engage. but DO NOT, DO NOT, DO NOT leave this switch jumped during normal operations just to use your A/C. This switch is a vital safety component for your system.
If your clutch engages with the terminals jumped, but does not engage when connected to the switch, either you have a bad low pressure switch or there is not enough refrigerant in your system to keep the switch in the closed position. You can leave it jumped long enough to charge your vehicle as a vapor if need be.
I believe you will find your low pressure switch to be the culprit, but if you do the above checks and still nothing, let me know and I will trace it further. But please include in your response either the pressures, how the system was charged, if he did liquid into the high side how many ounces went in.
Thank you for your question, and I hope I helped out a little.
