2001 Suburban Electric Fan conversion..... Fans run always.

Newbie question, I've searched a few threads on this topic, but many didn't lead anywhere, nor did their recommendations resolve. So I've converted my 2001 Suburban to using 2005+ HD fans using a Nelson Performance Fan Harness. Plugged the blue wire into Blue#42, Grounds, and Power etc. Then proceeded to enable 2-Fan in HPTuners and flash my PCM.


However, now my fans run constantly. As soon as engine is started. (Actually need to confirm if in ON vs RUN, etc.)

This Radiator (34in 2-Row Aluminum) is too efficient to have fans running constantly and allow the engine to come up to operating temp. We're talking ECT values not getting above ~150*F unless I manually disabled FAN 1 in VCM Scanner during a drive test...

Here are my settings, I need to confirm relay operation still (Should get that done this evening):

Attachment 108003

For starters, I would change the "Disable Speed" to something like 35 mph. Next it would be a good idea to log the AC pressure to see if it is over 500 psi.

Just a couple things to check...

Actually just came back from a run, decided to go back to default settings and ONLY control on/off via the ECT temp range for Stage 1. AC Circuit trigger removed.

Worked like a champ. I'll confirm Condition #2 and #3 testing at a later date when the temps get a bit warmer. Currently with this FAN/RAD combo it takes idling for ~20mins to get close to 190* with a 15mph crossbreeze @55F ambient outside.

Working Test config:
Attachment 108008

If the thermostat is closed, the radiator capacity or fan airflow should have zero effect on engine coolant warm-up time. It also shouldn't be able to pull the engine temp down below the thermostat opening temp.

I don't know how their harness works. Does it tap into the AC compressor clutch somewhere? It isn't trying to use red 33 blue 42 only right? That year truck did not have a A/C pressure sensor so the harness has to have a A/C trigger of some sort. If that is the case remember defrost will turn the A/C on and the fans on for that matter.


Our harness uses the ECM high and low outputs but mixes in a A/C signal to bump the fan speeds by one. So if AC comes on and the fans are off they go to low.. If the fans are on low and the ac comes on it goes to high.. etc.