Topic: A/C compressor wont kick on, but engine idles up??

[spc mike]

Hi guys, iam looking for help on my A/C. Im trying out that freeze 12 freon so i went through and put a new Napa expantion valve, reciever/drier, new ester 100 oil, flushed the evaporator and condenser and then evacuated the system.So now whats happening (with the system all evacuated and charged up) is the engine will idle up properly to compensate for the load of the compressor but the compressor itself wont kick on. However it will kick on if i jump it. My system functioned fine last summer when i was trying the 134a untill it eventually leaked out. However the 134a never really got that cold.

Sooooo. does anybody have and clues to what i might want to check or what it might be? Thanks in Advance guys!

[emsvitil]

Test the resistance of the compressor coil   (3.5 ohms +- .2)

[spc mike [OP]]

I will have to check that when my brother brings his voltmeter home today, but iam not even getting any power to the wire that goes directly to the compressor.

[hilux-1983]

Did I miss exactly what year this is?

[spc mike [OP]]

oh sorry, its an '85 carbed truck.

[emsvitil]

My 86 has a hidden fuse behind the glove box.

85 is probably the same.........

[spc mike [OP]]

ya, i got those too. both of those fuses behind the glove box are good.

[hilux-1983]

Is the thermal ground point have a good connection? I had the same issue and that's what the problem was.

[spc mike [OP]]

thats my other question. where is the thermo switch? I thought that had something to do with trucks equipped with tow package only.

[hilux-1983]

thats my other question. where is the thermo switch? I thought that had something to do with trucks equipped with tow package only.

This is a pic of the thermo switch. It supplies the ground for the a/c compressor to come on. The reason it's called a thermo switch is because it's a safety thermostatic switch that opens the circuit once the coolant temp get too high(what temp? you say. I don't know) It stays closed to supply the ground, otherwise. Make sure the connection is good and clean. You can also apply this to a direct ground if you wanted. Hope this helps.

[emsvitil]

This is a pic of the thermo switch. It supplies the ground for the a/c compressor to come on. The reason it's called a thermo switch is because it's a safety thermostatic switch that opens the circuit once the coolant temp get too high(what temp? you say. I don't know) It stays closed to supply the ground, otherwise. Make sure the connection is good and clean. You can also apply this to a direct ground if you wanted. Hope this helps.

If the AC compressor only has 1 wire (other side is grounded at compressor), there shouldn't be a thermo switch............
(that's if the thermo switch supplies the ground to the coil and not a relay)

[hilux-1983]

If the AC compressor only has 1 wire (other side is grounded at compressor), there shouldn't be a thermo switch............
(that's if the thermo switch supplies the ground to the coil and not a relay)

I've traced the whole a/c system over and over to fix this same problem. I kept coming up with the thermo switch(loss of a ground). When I finally found what the heck the thermo switch was, where it was and what it did, I have NO more electrical issues. But, to test this theory of mine, jump the wire that goes to the thermo switch to ground and see if the a/c system comes alive.  Oh, and to answer your question about the "coil or relay", your partly right.  The wire that goes to the thermo switch goes into the cab on the passenger side into combination of a relay, a/c amplifier and such. Most of the "magic" happens right there on the passenger side kick panel.  I am NOT in any way saying this is spc mike's problem, I'm just throwing in my 2cents from my experience.  Furthermore, the thermo switch completes the circuit by supplying a ground.  It's a safety switch. The engineers put it there for the sole purpose of shutting down the a/c if and when the vehicle's engine cooling system started to overheat. This would stop the a/c from engaging hence, the excessive addition of the heat from the condensor onto the radiator, therefore helping in cooling the engine cooling system down. So, as long as the vehicle is not overheating, the thermo switch stays closed(supplying ground) I hope I'm making sense. 

[Rocksurfer]

My truck did this, it was due to low pressure in the system. There is a low pressure sensor that kicks the compressor off if there is not enough pressure in the system.

[crazykooter]

I agree with the last post.  It more common to have low pressure after flushing the ac and refilling it.  Also that freeze 12 stuff is a rather harsh substitute for r12.  Beware it destroys the compressor seals.  It will work for a while but in time your gonna have to replace your whole ac setup. 
How long did you vac the system before you refilled the freon ? Did it hold the vacuum for more then 15 mins ?  I have some real r12 still left if your near me.  Recheck the freon level.  If its good then you might want to try to ground out that thermal switch.  Then let the ac run for a little bit. 

[spc mike [OP]]

I don't have a thermo switch. My thermostat housing just has a blank recessed hole where it should be. Mind you my truck didn't have ac from the factory, it was added from the previous owner. I evacuated for about 20-25 min and it held vacuum for the 15 min we allowed it. Where are you located I wouldn't mind have some real r12 in my system. What's a good way to check that you have enough freon in the system?