QuestionThe air conditioning compressor clutch is not going on. I checked the fuse and is ok. Is it possible the air conditioning clutch relay could be bad?
AnswerThat is always a possibility, but before we go replacing parts, start here.
If your refrigerant charge is low, this will prevent your clutch from engaging. See if you can get your hands on a set of gauges and check your pressure.
There are two safety switches inside your A/C system whose whole purpose in life is to protect your compressor. A low pressure switch which prevents your compressor from running when the pressure drops below a certain point. And a high pressure switch which disengages your compressor if the pressure climbs too high.
The one I want you to concentrate on is the low pressure switch. Locate this switch. Usually it is located on your accumulator (an aluminum canister about the girth of a soda can with two lines coming out of the top of it) If it is not there, trace your low side line and you will find it. Disconnect the harness from this switch. With a small insulated wire, jump the connector in the wiring harness. Turn the key to the run position and turn the A/C switch on. You should hear the clutch engage. If it does, the relay is fine, and you need to look at a leak and low refrigerant charge. If you have refrigerant in the system, then I would recommend replacing the low pressure switch. Depending on the veihcle this is usually about 15- 45 bucks. If the clutch still doesn't engage, that would lead me to believe that the fault is prior to this switch, which along with other wires, the relay is. If it does not come let's move on to the relay.
ON 80 percent of relays, they have a drwaing of the contacts on the casing. With a multimeter, check the coil terminals for voltage, (A/C switch on, of course) You should read 12-14 volts across the coil. If you read no voltage across the coil, then you will have to trace the schematics for your vehicle further back to see where the relay is getting energized from. If you have 12 volts on the coil, check the contact terminals. There should be 3 contact terminals. Let's call them A, B, and C. A is the input voltage. With the A/C switch off you should read voltage or have continuity between terminals A (input) and B (a dead end for the voltage.) With the A/C on and 12 volts at the coil of this relay, the contacts should switch to having voltage or continuity between A (input) and C (out to your low pressure switch) If there is 12 volts energizing the coil, and the contacts do not flip from A-B to A-C, then yes your relay is bad.
In short, check your refrigerant charge. Low refrigerant=Low pressure. Low pressure disengages your low pressure switch thereby shutting down your compressor. If there is no way you can get gauges on your truck, leave the switch bypassed and turn the engine and A/C on. If the evaporator fan (inside) is blowing cold, your charge is fine. Replace your switch. If it is blowing hot, get your leak repaired and system charged. Some places call it by low pressure switch, others (autozone) call it the compressor cycling switch. You do not have to remove the refrigerant to replace this. Simply unscrew the old, and screw the new one on. There is a schraeder valve below it to prevent refrigerant loss during replacement. But, and I dont mean to insult your intelligence by any means, but I have to say it. DO NOT, DO NOT, DO NOT leave that switched bypassed for normal use. This will cause extensive and expensive dameage to your system.
If your compressor does not come on with this switch bypassed, check your relay by the method above. If your relay checks good, I recommend taking it to a reputable garage to have the wiring troubleshot. Unless you are good at tracking and tracing schematics, Then it should be no problem.
I hope I was of a little help, and thank you for your question.
