Hello I will help you with your question,
There cannot be any engine faults or the system will not turn on. Do you have a check engine light on?
If no check engine light do all the controls for the AC/heat work correctly?
Do you have a voltmeter or a testlight?
OK to turn the relay for the compressor on you need the thermistor in the evaporator to allow it and the pressure switch for the high and low pressure.
When you ran it by jumping the relay did it cool normally?
Ok then I need to know if you have a digital display or is it all buttons and knobs?
If digital hold the auto button while turning the key to run then press the AMB button four times in 2 second after turning the key on. Wait for the system to check and see what comes up on the display.
In addition to the thermistor the ambient sensor needs to be in a certain range and if you have an air quality sensor it needs to be happy as well. You can tell if you have an AQS by the "A" in a circle in the center lower button.
Let me know if you get any codes
18 says the thermistor in the evaporator is shorted.
You can remove the evaporator (dash removal) and replace the sensor or you can cut the two blue wires coming out of the evap case and solder a new sensor head onto the wires and heatshink insulate them .
It is not recommended that the wires be soldered but it has been done successfully in the past.
The thermistor head is clipped onto the HVAC case behind and slightly to the left of the glove box. You can get to it from under the vehicle and a new sensor (thermistor) is about $80. There is a transistor in the head so that is what has shorted.
The thermistor keeps the evaporator from turning into a block of ice by cycling the compressor.
Let me know how I can help you with this
Once the new sensor is solder in where does it get installed to
Back in the same holder on the outside of the HVAC case, Look under the dash by the glove box (remove the sound insulator from under the dash ) and you will see the sensor head in its holder with the two blue wires running into the case.
Glad to help and please let me know if you have further questions