Senna

iTrader: (1)

I'm trying to understand how to activate dual fans with AC.

I have an E38 PCM and a SPEARTECH harness, Vintage air and dual fans.

Speartech calls for fan One and fan Two. the harness has dedicated 12v + (keyed) and ground (switched) signal for each fans.

So when I add AC now I need to activate both fans at AC on through trinary switch.

When I contacted speartech they said to split the AC on signal to each relay.
My concern is that when I combine both relays to the one AC on signal that I am essentially tying the fan one and fan two signal from the pcm together and both fans will come on when just fan one is activated by pcm.

My thinking is that I will need two additional relays to keep the signals separated, correct?

DW SD

I believe E38 has fan high and low. If so you could turn one fan on or two. One would be for Low and Two for high. . various features exist and temps need to be set properly for Low and high.

Yes you need different relays to keep the controls separate.

Use a busbar or isolated junction stud to join the input 12v+ for one of the fans. One input from AC triggered relay and the other from the pcm triggered relay but the relays are separate.

If it was me I’d have the AC call for just one fan via trinary when pressure hits threshold and the pcm call for one fan at Low and then both at high speed. If not Low and high features exist then have the pcm trigger both fan relays when temp criterion met.

DW SD

If you set it up like I suggest...
1 relay for AC triggered fan.
1 relay for pcm triggered Low to 1 fan (output to other fan from AC fan. )
1 relay for pcm triggered high - both.
use a small bus bar or isolated junction stud at each to join the outputs from each relay.
I run this setup but with one 16” Spal fan. Trinary or pcm can control fan separately. For me just two relays.

Senna

iTrader: (1)

I guess my next question is, Is one fan enough to pull plenty of air across the condenser for sufficient AC operation? wouldn't it be possible for the AC to build to much pressure and shut down before the the pcm sensed high enough temp to activate the second fan?

DW SD

My fan pulls enough air even when hot ambient to cycle the fan off and on. Might have 30 seconds off. Some Trinary switch will also serve as safety if pressures get too hig and interrupt compressor clutch.

Ach1992880

You could put diodes in the AC signal wires to keep from feedback triggering the second fan. Think of diodes as a one-way valve for electricity.

DW SD

Senna

iTrader: (1)

I had this though, but don't know much about it.

I just went to youtube and did some research. All the info I saw indicated a positive and negative connection to the diode. In the relay application wouldn't it be negative and negative?

DW SD

Senna

iTrader: (1)

Looks like this dual contact relay could be the answer.

https://www.delcity.net/images/lined...20170424182941

DT69cam

I would consider the Entropy Fan controller set-up. I would install it as a stand alone system. I have it. You can adjust fan temps etc. Its a nice set-up. http://www.entropyrad.com/lsx-series...ontroller.html

Senna

iTrader: (1)

Thanks, but I believe the dual contact relay I posted above is all I need. The pcm already controls the fans in a high/low configuration and the relay will let the AC turn on the fans when necessary.

DW SD

Did you see this thread?

DW SD

Another option would be to use the factory pressure switch and enable via ECM. Then the relay wiring becomes greatly simplified. Just high and low.

DW SD

I think that would work for the PCM high, but it doesn't have dual input circuits. You really want to have separate trigger circuits from the PCM and trinary.

Lots of ways to skin this one.

Doug

Senna

iTrader: (1)

Yea, I don't know which way I am going to go.

My thought on the dual contact relay was, one signal in from trinary and two signals out to each fan. That way I would avoid tying the two fan signals from the pcm together which would cause them to act as one instead of individuals. But as do research it apears the pcm could set a CEL if it sees an unauthorized ground.

I like the idea of diodes but the information I have gathered is not conclusive.

DT69cam

That Entropy controller is looking pretty good LOL

showdog75

iTrader: (8)

I haven't got mine up and running yet but my BP automotive harness has the pressure switch built in and uses a binary and 3 relays controlled through the ecm... ugh my head hurts

Senna

iTrader: (1)

I'm not in a huge hurry. I still believe it can be done for the cost of a relay or some diodes.

Senna

iTrader: (1)

My son was over last night, we were talking about the AC and controlling the fans and he had a suggestion that sounds like a good solution.

His suggestion was to use two additional relays and instead of combining the signals from the pcm and trinary to combine the battery + leads going to the fan motors. Basically two complete separate systems both powering the fans.

So this way there is no back feeding issues or no unauthorized grounds to set a CEL.