Hello to all my friends
Here I am …. What is exactly the doubt about the connections of that FRIKING AC unit?
ERIK, any A/C system is connected more or less with the same principle at the EVAPORATOR CORE(console, where cold air comes out in the cabin)
There is first a BLOWER MOTOR SWITCH. This generally has 5 legs.
1. Source of 12V from a T15 circuit (only energized when car ignition on RUN position)
2. 12V output for Speed I for the blower motor
3. 12V output for Speed II for the blower motor
4. 12V output for Speed III for the blower motor
5. 12V output for the temperature switch, hot in all positions I, II, III
This last leg or terminal you will identify it on this way.
Find a multimeter, put it on continuity testing function. Put one terminal fixed on the leg that correspond to the INPUT for the switch. Move the switch to speed I. See which terminals/legs have continuity with input terminal at this position.
Repeat the procedure for each speed. You will notice that for each blower speed position there are always two pins which have continuity.
That is because the leg/terminal that feeds the thermostat switch at the ac console should have power always when the blower fan is activated either on speed I, II or III
So once the blower switch terminal that goes to thermostat switch is identified run a cable from that leg to either side of the thermostat switch. The second terminal at the thermostat switch is the OUTPUT that will turn ON your AC compressor CLUTCH
So on the simplest approach for a wiring harness to control your AC system, that Compressor activation signal that comes out from the temperature switch should be run to the engine bay, where at least you should have a relay to control the condenser fan an A/c compressor clutch.
That signal just mentioned before should be connected in that approach to terminal 86 on a standard 4 prong relay. Terminal 85 directly to ground. Then terminal 30 should be fed through a fused source coming from battery, and finally terminal 87 output is used to turn on the ac compressor clutch and the condenser fan at the radiator.
There are many ways to solve the wiring harness for an ac system. That described before is the simplest, which I do not use in my projects. There are other ways, which I like it more that involve more components and logic to make the system more robust, and to reduce the stress on the charging system. Not in every circumstance a condenser fan is required to run at the same time as ac clutch. It really should run only when a set pressure is reached inside the refrigerant gas, and for that you need another control element called trinary switch that is installed on the drier desiccant filter.
See figure attached below.
If any of you want a more professional wiring harness for that purpose feel free to contact me.
Best regards
L.Peterssen
