Heat exchanger fan wiring

Tim Moland

Well-Known Member
Wiring is definitely not my strong suite. I'm trying to wire up a heat exchanger fan for key on operation. Lonny has laid out where to tap into the bcm plug to get power. It is 2 wires that get wired into one. But one of the wires in the terminal in my BCM plug appears to be used on something already. The second one is cut. The harness was assembled by DF, so I don't know what it goes to.
20210219_012634.jpg
I'm running a heat exchanger in the engine compartment, so I will be running it to the back of the car. Is there a different terminal I can tap into that will be powerful enough for the fan?
 

JPas914

Well-Known Member
You could build a relay, and use the ABS circuit/fuse as the trigger to activate it since it is still being powered when the key is turned on. My heat exchanger pump and fan were a slight after thought when I had built my Goblin.
 

Rttoys

Goblin Guru
Yes. That can be a trigger for a relay. You can use a “Bosch” relay or a 4 prong. I need to find my little tutorial I made years ago, but basically you have 12v power in (from batt). 12v power out to fan (when triggered). One ground and one ignition positive to trigger the relay. Don’t be afraid of them, they make life simple.
 

Tim Moland

Well-Known Member
Ok, I'm thoroughly confused. Like I said, wiring is not my strong suit. Why would I do all this relay stuff as opposed to just wiring direct to the BCM plug? I don't understand wiring
 

JPas914

Well-Known Member
It's all just like the saying 'there's more than one way to skin a cat'.

The relay will power the fan and pump when activated by the trigger, which would keep the amperage draw on that wire down. You can easily buy a small 'add-a-fuse' plug at Autozone to tie into the ABS fuse. it help keep all the wiring in the back without needing to run it through the tunnel, or worrying about where that one wire goes to. Building the relay is a very simple process.
 

Rttoys

Goblin Guru
If it was a low amperage item being added (like led lights), just adding the wire would be fine, because the bcm can handle it. Adding a higher amperage item like a fan, it’s best to add a relay so it handles the load and the bcm is nothing but a trigger. I did the same thing to mine because I added a larger inter cooler fan than DF provided.
 

ncgoblin

Goblin Guru
Reviving this thread. I too am not an expert with electrical but I noticed there are (2) 30Amp Relays in the PCM that are for cooling fan 1 and 2. I imagine 1 is for the front mounted radiator fan would it be possible to use Cooling fan 2 for the heat exchanger fan mounted in the rear without having to purchase a Bosch Relay?

The next question are these (2) circuits triggered based on the engine temp or just the radiator fan?
 

Ross

Goblin Guru
Fan 1 is turned on by the coolant temperature, and Fan 2 is triggered by the air conditioning R134A pressure sensor.
Our LSJ has the ablility to run Fan 1 and Fan2 in both parallel and series, which will run the fans at 12V or 6V. In the goblin we don't use the 6V low speed fan setting, the R134A sensor or Fan 2. You could replace the R134A sensor with a different 5V sensor, and program it to turn on at new voltage levels.
 

Gtstorey

Goblin Guru
Cobalt is set up with two fans triggered in series for low speed and in parallel for high speed based upon Engine Coolant Temp AND/OR AC Pressure, at least on the later model.

I'm not sure that the work required to rewire it to try and use the existing relay is worth the effort. What is your control scheme for cutting on a heat exchanger fan. I have mine set up with a 5 pin relay to come on with ignition power on the normally closed portion of the relay, and a switch to open the relay if I don't want the fans to be running (with a bright red light on the dash as a reminder that it is off). You can get a (5) x 5pin 30a relay with pigtail for less than $12.
5-20Pcs DC 12V 30/40 Amp Car SPDT Automotive Relay 5 Pin With Harness Socket Set | eBay
 

ncgoblin

Goblin Guru
Cobalt is set up with two fans triggered in series for low speed and in parallel for high speed based upon Engine Coolant Temp AND/OR AC Pressure, at least on the later model.

I'm not sure that the work required to rewire it to try and use the existing relay is worth the effort. What is your control scheme for cutting on a heat exchanger fan. I have mine set up with a 5 pin relay to come on with ignition power on the normally closed portion of the relay, and a switch to open the relay if I don't want the fans to be running (with a bright red light on the dash as a reminder that it is off). You can get a (5) x 5pin 30a relay with pigtail for less than $12.
5-20Pcs DC 12V 30/40 Amp Car SPDT Automotive Relay 5 Pin With Harness Socket Set | eBay
This may be the easiest solution. Based on the guide below which circuits would you suggest tieing into at the rear?

39591


Example as shown above would the Fuel Pump wiring be required?
39593
 

Desert Sasqwatch

Goblin Guru
Idea: since most any vehicle equipped with air conditioning will have some kind of fan override to turn it on when the AC is turned on, would it be possible to fool the system with a dummy AC switch to turn on the fan(s) manually?
 

Gtstorey

Goblin Guru
On second thought, I think I ran the ignition on positive through my switch NC contacts and used that to close the relay, and did not use the NC portion of the relay. Push the switch and it swaps to NO contacts killing the relay and powering my warning light. I don't remember what circuit I used for ignition on power. I used one of the OEM circuits that closes aa added relay that then feeds a mini fuse box to power to several circuits. The load side of the relay is powered directly off the jump post at the fuse box with an inline fuse.

I actually have 2 separate fuse panels behind my dash panel, one powered by ignition on relay, one always hot.

I just leave my fans on most of the time, only turning them off during warm up, talking to someone when the car is running, or when Uploading a tune adjustment. You never know when you might need boost. If I was going to do any control beyond that I would do it based upon the Coolant temp, or maybe boost pressure with a timer.
 

ncgoblin

Goblin Guru
On second thought, I think I ran the ignition on positive through my switch NC contacts and used that to close the relay, and did not use the NC portion of the relay. Push the switch and it swaps to NO contacts killing the relay and powering my warning light. I don't remember what circuit I used for ignition on power. I used one of the OEM circuits that closes aa added relay that then feeds a mini fuse box to power to several circuits. The load side of the relay is powered directly off the jump post at the fuse box with an inline fuse.

I actually have 2 separate fuse panels behind my dash panel, one powered by ignition on relay, one always hot.

I just leave my fans on most of the time, only turning them off during warm up, talking to someone when the car is running, or when Uploading a tune adjustment. You never know when you might need boost. If I was going to do any control beyond that I would do it based upon the Coolant temp, or maybe boost pressure with a timer.
With all the small custom circuits adding up I am at the point where I may just build a dash panel to keep the always on/ignition on circuits.

Is this something you went with?
 

Gtstorey

Goblin Guru
Yes, I have one of those although it may be either 8 or 10 circuits. This is for my ignition on power. I have a smaller one that is always hot power. I like the style you linked since it has a bar for ground distribution. It's easier to tie small load circuits for gauges and similar into it than to try and land them all on a stud.
 

Sluggonaut

Goblin Guru
I went with a ground distribution block for all the small stuff, but wishing I did the same for accessory power. I may be adding this to my to-do list.
 
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