Dual Fans - Vintage Air - ProFlo-4 ECU

[PbFut]

The ecu needs clean travel paths. The fan trigger wires are internal electronic switched to ground. Only one relay coil is to be connected to the fan leads. The ecu can't handle anything else. Ignore the trinary switch. There should be a wire that needs +12v into the ecu when ac is on. Best if you can pull from compressor but could be tricky and need a relay if the compressor is switch on the negative side. If so, you will have to add a relay to turn the negative side swith to a +12v signal. Depending on ecu, there will be 1 2 or 3 fan triggers. Some only trigger fan 3 for ac. You can not cross or share relays. If you have 2 fans and 3 triggers, you need to get a dpdt relay for fan 3 and do some tricky wiring to keep all 3 ecu triggers isolated and control only 2 fan relays. I did on my system and works correctly. Also, the +12v side of the relay coils needs to go to battery. You don't want noise back feed into those 3 ecu trigger wires. The ECU is very susceptible to dirty power.