Gen 1 radiator fan controller upgrade

[Walter Clark]

This is some details of my little project to improve the management of engine cooling by using a dedicated controller to run the existing fan controller relays in my 1994 Viper.

I strongly recommend you have a copy of the service manual to have access to the vehicle wiring diagrams. This way you can verify the connector/pin location and correct wire color of the 5 wires that the controller needs to be connected to, and to identify the correct wires in the wiring modification for your vehicle.

I chose the Dakota Digital PAC-2800BT controller. It is wired up and calibrated to read the output of the stock temperature gauge sensor and configured to sequence the low speed relay and hi/low changeover relay to control the stock dual speed fan.

Modifications to stock wiring are all in the wiring harness leading to the low and hi/low relays or the at the plug of the ECU/MCU, on the underhood side of the passenger footwell bulkhead. All the wiring to the controller passes through a small grommet I installed just inboard of the 50-pin connector and the controller itself is attached to the fuse box cover with 3M Dual-Lock strips.

I changed the ignition ON switched 12V to the fan relays coils to a constant 12V by cutting the dark blue wire that goes from the AC relay coil switched 12V feed to the fan relays and splicing the end going to the fan relays into the gray constant 12V wire that feeds power to the normally open contacts of these relays. This allows the Dakota controller to continue to run the fans after the engine is shut down if the coolant temp is above either the fan low or fan high ON thresholds. The time this runs is user settable. To energize the fan relays, the MCU and the Dakota controller ground the other side of the coils.

I cut the 2 control wires from the MCU that energize the fan relays and spliced in 2 wires leading to the Dakota controller FAN LOW and FAN HIGH terminals. I did the splices at the MCU connector, but it could also have been done at the relay ends of the harness. I chose the connector end because it allowed space for me to put spade connectors on the wires going into the MCU, the original wires feeding the relays and the new wires going to the Dakota. I can then revert to the stock setup if I need to for some reason by just removing the connector cover and reconnecting the MCU to the relay control wire.

For this part of the description I will use the labels on the Dakota controller to describe the other wires...I picked up BATTERY+ from the gray wire feeding the fan relays and IGNITION from the Blue wire from the AC relay that I cut above. For the SENDER signal I spliced into the temperature gauge sensor wire where it goes into the 50-pin bulkhead connector. I tied ground for the controller to the ground lug below the wiring harness going to the passenger footwell. I have not, as yet, connected the DISABLE- signal. This is a ground when active and could be useful to stop the fans during engine startup so-as to reduce the load on the battery when starting the car. There is supposed to be an unused connection on the starter switch which supplies a ground when the ignition switch is in the START position. I have not verified this to be true.

I have attached a simplified wiring diagram of my install. I also attached a screenshot of the bluetooth app for the Dakota Digital controller showing my settings. The key setting not shown is the fan mode. It should be in the TWO FAN mode since the Viper 2 speed fan requires BOTH the Low and High inputs be driven for high speed operation. The Dakota controller 2 SPEED FAN mode operates either the low or high relay so will not for this particular motor.

 

[Walter Clark]

So how does it work in the car? With the settings I have shown, 80 degree ambient air temps, using a 190 degree thermostat and a Rowe radiator - under normal driving, and in stop and go traffic, the temp gauge hangs in between about 195 and 200. The worst case I have seen so far is when I drove up a long (4 miles) very windy road in 2nd gear at under 30 mph and stopped the car for maybe 4 minutes at the summit. While stopped with no air moving through the radiator the temp quickly started upwards and first the low speed fan came on then the high and the temp peaked just above about 210 at which point the temps started back down. Before I drove off, the fan had switched back to low speed and once moving again the temps quickly came back into the 195-200 range. This is much less deviation than I have experienced with the stock controls in place.

I know the Rowe radiator will cool the engine better than the stock radiator when the car is moving, but without air moving thru the radiator it heat saturates as well. I experienced this in spades on day a couple months back when I decided to back the car out of the garage and do a quick wash to get the dust off, while leaving it idling. Unbeknownst to me, the low speed relay had failed sometime earlier and the fan could not be turned on in either low or high speed. Before I got done washing, the engine temp shot way up. My first indication of a problem was when I noticed coolant being dumped on the ground from the overflow tank. I subsequently corrected that problem, but decided to also work on trying to control the range the coolant temp experiences better.

 

[DickDavis]

This is some details of my little project to improve the management of engine cooling by using a dedicated controller to run the existing fan controller relays in my 1994 Viper.

I strongly recommend you have a copy of the service manual to have access to the vehicle wiring diagrams. This way you can verify the connector/pin location and correct wire color of the 5 wires that the controller needs to be connected to, and to identify the correct wires in the wiring modification for your vehicle.

I chose the Dakota Digital PAC-2800BT controller. It is wired up and calibrated to read the output of the stock temperature gauge sensor and configured to sequence the low speed relay and hi/low changeover relay to control the stock dual speed fan.

Modifications to stock wiring are all in the wiring harness leading to the low and hi/low relays or the at the plug of the ECU/MCU, on the underhood side of the passenger footwell bulkhead. All the wiring to the controller passes through a small grommet I installed just inboard of the 50-pin connector and the controller itself is attached to the fuse box cover with 3M Dual-Lock strips.

I changed the ignition ON switched 12V to the fan relays coils to a constant 12V by cutting the dark blue wire that goes from the AC relay coil switched 12V feed to the fan relays and splicing the end going to the fan relays into the gray constant 12V wire that feeds power to the normally open contacts of these relays. This allows the Dakota controller to continue to run the fans after the engine is shut down if the coolant temp is above either the fan low or fan high ON thresholds. The time this runs is user settable. To energize the fan relays, the MCU and the Dakota controller ground the other side of the coils.

I cut the 2 control wires from the MCU that energize the fan relays and spliced in 2 wires leading to the Dakota controller FAN LOW and FAN HIGH terminals. I did the splices at the MCU connector, but it could also have been done at the relay ends of the harness. I chose the connector end because it allowed space for me to put spade connectors on the wires going into the MCU, the original wires feeding the relays and the new wires going to the Dakota. I can then revert to the stock setup if I need to for some reason by just removing the connector cover and reconnecting the MCU to the relay control wire.

For this part of the description I will use the labels on the Dakota controller to describe the other wires...I picked up BATTERY+ from the gray wire feeding the fan relays and IGNITION from the Blue wire from the AC relay that I cut above. For the SENDER signal I spliced into the temperature gauge sensor wire where it goes into the 50-pin bulkhead connector. I tied ground for the controller to the ground lug below the wiring harness going to the passenger footwell. I have not, as yet, connected the DISABLE- signal. This is a ground when active and could be useful to stop the fans during engine startup so-as to reduce the load on the battery when starting the car. There is supposed to be an unused connection on the starter switch which supplies a ground when the ignition switch is in the START position. I have not verified this to be true.

I have attached a simplified wiring diagram of my install. I also attached a screenshot of the bluetooth app for the Dakota Digital controller showing my settings. The key setting not shown is the fan mode. It should be in the TWO FAN mode since the Viper 2 speed fan requires BOTH the Low and High inputs be driven for high speed operation. The Dakota controller 2 SPEED FAN mode operates either the low or high relay so will not for this particular motor.

Did you take any video or photos? Your fix sounds great but images are very helpful. Would you be able and willing to do this to somebody else's car?