How can you test a a/c relay? I have a 94 jimmy and the a/c doesn't work can they be tested, or hope for the b

I own a shop, and the easiest way is to bench test it. Remove it from the vehicle, and use a nine volt battery like goes in a walkman. On the relay you will see a diagram. Two of the terminals are what is called the latch. The latch is what pulls the relay into operation once the switch activates the circuit. You will see a little symbol that looks like a coil, and some numbers %26amp; letters on it. Hook the battery to the ones that activate the coil, and you should hear a clicking sound. If it doesn't click, its no good. Don't worry about hooking it wrong, as the battery won't harm the relay. Since you will only attach the battery momentarly, it won't hurt a thing. You can use an ohms meter to attach to the other lines on it to make sure they are switching when the latch is pulled in. The answer before me is correct for the testing procedure, so follow those instructions to hook it up. You should remember a relay is only a directional switch, power is allowed to go one way, pull in the latch, and it goes another way. There is nothing inside you will burn up with the battery, so even if it is hooked wrong, it won't hurt a thing unless you leave it hooked up that way for any length of time, but 9 volt battries will go dead pretty quick if they are shorted out. You have power in, and a latch that directs it to go somewhere, or not. If you suspect the clutch is bad, unhook it, and use a wire off the hot (+) on the battery to test the clutch. If it clicks when you hit it with power, it is good. There is also a pressure switch that can be tested by bypassing it with a jumper wire to activate the compressor clutch. Being low on refrigerant will cause the switch to not activate, and make you think its a bad switch, so jumping it out is the test to do for this. You would have to put a gauge on it to tell if it is low on pressure, if it is, the pressure switch is bad. If you hook power directly to the compressor clutch, make sure you aren't hooking it to the ground (-) side of the connector, or you will make sparks fly, and could damage the alternator. The two terminals on the compressor are; one is hot, the other is ground. It is better to unplug it, and use an outside power supply to test it with, and that way you don't risk hooking it wrong and causing damage to the alternator.


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I own a 94 Blazer (which is the same as yours) and this system is built "cheap". I bought it new, and have replace the switch on the dash about once every three years. It can be replaced pretty easy, just take out four screws to access the control assembly, unplug the wires going to the switch, remove one screw (8mm) and its out. The knob for it will usually break, so use a pair of needle nose to push under it, and the taper of them will push the knob off. The switch is too cheap made to carry that kind of amps, and should have been recalled. The relay is on the firewall just above the passenger side valve cover. I've replaced it a few times too. If you hit it with a screwdrive, and the blower goes to working, it's bad and needs replaced. Also; in the heater box near the blower motor is a resistor (that has four or five wires going to it) with two 1/4" socket screws to hold it in. Remove it and take a look at the coils in it (that look like springs), one may be burned in two, and you have to get it from the dealer as a regular parts store either doesn't carry it, or has to order it. If you have no blower, tap on the relay to see if it comes on with it in the high position. Inspect the resistor, and if it's good, replace the switch. Look at the wires that plug onto the relay for bad connection, and clean it. Add a small amount of grease to all connections to keep them from corroding. I have repaired mine so many times, I now think I'm an expert on them. This has got to be the cheapest, most tacky system I have ever seen on a system that carries so much amps. The switch, the relay, and the resistor are all too cheap to do the job.


Glad to help out, Good Luck!!!

How can you test a a/c relay? I have a 94 jimmy and the a/c doesn't work can they be tested, or hope for the b
A 94 should have old-fashioned Bosch-style relays. First off, make sure you have refrigerant in the system. Without refrigerant pressure, the low side cutout switch(the little 2 wire switch on the accumulator, near the firewall and blower motor, passenger side) will not allow the relay to send power the compressor. Unplug and briefly jump the wires at that switch. If a/c kicks in, check the switch for continuity and replace if nessessary. Find the relay that has the same color wires coming out as the a/c plug @ the compresspor has. Pull the relay and look at the terminals on the back of it. There will be a 30, an 87, an 85 and 86. 85 %26amp; 86 are the trigger side. putting power from a battery to 85 and grounding 86 should close the relay and show continuity across 30 %26amp; 87. No power relay will open. if the part passes, jump across the wires in the relay's plug on the car at 30 and 87. 30 should be hot and 87 should lead to the powered accesory. if the a/c then works, you prob need a new relay. A/c is a little complicated, but the theory is simple. Look, if you can, at the wiring diagram in a Haynes or Chilton manual, the current flow is pretty simple. Good luck.
Reply:there should be a set of relays on the back firewall on a 94. all 3 are the same. just move them around and see if that makes any difference.

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