My AC compressor won't kick on unless I take 12V from the battery through an alligator clamp with an open wire on the other end and insert the "hot" end into one side of the switch (circled in picture, yellow and black wire side I believe). The compressor immediately kicks on and blows cold air but when the power is removed it shuts off.

What could be wrong? I know some wiring isn't complete, but where? What?

Sorry for stealing your engine bay pic.

 

you need to change the switch that the harness plugs into...

question, with the ac turned on an dblowing hot air, before you unplug the harness is the ac fans on or off?

if it is on, when u unplug the harness does the fans cut off?

 

The fans are blowing air regardless of the harness being plugged in or out.

 

Did you recently install an AEM or change your MAP? Mine did the same thing because the clutch was turned off in the AEM EMS. Here is the link I used to fix it.

https://www.evolutionm.net/forums/sh...a%2Fc+disabled

Hope that helps.

 

that's funny cause i have a similar problem.

my car blows hot air if i drive it for a while and it builds heat. then if i turn on the ac it will blow hot air until
1: i drive on the highway and air flows through the engine compartment
2: rains falls and the place cools down, or i let eh car cool way down.

if i turn the ac on when the car is cool, it will work PERFECTLY for my whole trip. but if i switch off and the car sit in the sun for a while and i come back.. its hot air till the above is met

if i unplug the harness in question my fans cut off. if i plug it back in the fans work but still no cold air.

i need to run a direct wire to the harness from the battery and see if the ac will blow cold.


you however mostly likely need to replace the pressure switch (the part you are plugging in the harness to) i have heard of many evos where this part has gone bad

here is how u can test it

let me know if it works

 

No AEM. Sorry.

 

The AC has never worked since I got it from Mitsu. Since I bought it in the Winter I never even bothered to test the AC until about a month ago. I'll try to test the switch MadCrix and see if it helps but the fans do stay on plugged in or not and I don't think cooler temps help I will try to verify by driving at night but I don't think I get cold air without the compressor coming on (any cooler than ambient which if its 65 outside I'll just drop the windows down anywyas)

 

The sensor your are pointing to is the head pressure sensor. If the sensor reads low psi in the system it will not let the a/c compressor turn on. The compressor receives its lubrication from the pag oil in the freon. If there is not enough freon to carry the oil through the system the a/c compressor will not engage, to avoid compressor lockup(think of running an engine with no oil... ). Jumping this sensor with battery voltage is simply tricking the ecu into thinking there is enough freon in the system to engage the compressor. Check the pressure levels in the system or just purchase a can of r134a and put into the system on the low side(big hose). Then try the a/c again. If this does not work you will have to use a vacuum pump to remove any remaining freon and recharge under vacuum to "suck" the freon back in. Also that small sight glass next to the sensor can tell you if you have air in the system. Look For bubbles while a/c is running. Good Luck.

 

+1 this is the problem. You have and leak or you are low on refrigerant or both.

 

+1 unfortunately, even with a full freon it will still bubble unlike the old R12. I would just check for the pressure. I have not check my evo but if there is a pressure switch near the receiver/drier(long silver cylinder) that can also be the defective. I think you can check it with an ohmmeter if the switch is still useful or not.