Electric fans & Vintage Air

[ls1nova71]

Originally Posted by Rich84

Finally had a hot day. AC works great. I tied the trinary to the high speed trigger wire. One fan runs at high speed. I’m not sure what will happen if the engine reaches the temperature to trigger the low speed. I’m not sure it ever will as it seems to keep it pretty cool with the one fan.

If you're using a 3 relay set up, and tie the trinary switch to the high side, it will only turn on one fan like you're seeing, but it should be alright. If the engine reaches the point it needs the low fans to come on, then both fans will run on high. It will be perfectly fine running this way as long as one fan is enough to keep the condenser cool, however most of the time in the summer when it's hot enough to need A/C the low fan will already be on so both fans will come on high when the trinary switch commands the fans on which should be sufficient to cool the condenser.

Originally Posted by First c10

If low speed is one fan (fan1)and high speed is the addition of the second fan(fan2) then the trinary switch will call for high speed fan(fan2) to be on as long as ac is on. If the engine reached the low temp set point in the pcm then fan1 will come on and both fans will be on.
I didn’t use a trinary switch I just added a relay so when I turn on the ac it turns on high speed fan. I used the original ac system binary switch for compressor protection only.

A trinary switch will not keep the fans on the entire time the A/C is on, it only turns the fans on when the head pressure is high enough to require it. So for example, at highway speeds the condenser is getting as much air as it will ever get so the head pressure will be low and the fans wont be running all the time. Similar to the way the PCM shuts the fans off above a set speed, somewhere around 40mph. It will add life to the fans not running all the time, and some have speculated that fans running at highway speeds can actually hinder air flow, although I'm not real sure about that.