2009 John Deere 6430 Premium HVAC fan runs with the key OFF

Lynn Ross · May 6, 2019

Hi Guys! Im new here and cannot find anyone that has posted about this problem. First, I purchased this tractor recently at an auction. 750 hrs. Back glass busted out of it. Been sitting outside on and off for the last 5 years barely moved. Thats all the history I have on it. At the sale I noticed the HVAC fan coming on and off with the key OFF while it was sitting in the sale line. Turn the key ON, and the HVAC fan turns OFF. Bought it, brought home and started looking for the problem. Found a mouse bed behind the HVAC controls in the headliner, a few of the small wires for the HVAC controls had been nibbled on but no broken wires at all. Taped them up. The HVAC panel light up as it should, the red and blue lights come on and off with the respective button, the vent selector works as it should, but the fan speed control does nothing. Also, the wiper, and all lights do not work. The lights on the front corners of the hood will flash on for a split second when the light swith on the dash is moved to the on position. All the blinkers work as they should. Radio work perfectly. Engine, transmission perform as they should. We have taken the entire cab apart and traced all wiring to make sure there is no more rodent damage. Taken the cab top off to make sure there is no damage above the headliner. No blown fuses across the entire panel. Panel is not corroded at all. Relays swapped out. Diodes replaced. Grounds cleaned. Still key OFF power going to the fans..... Anyone experienced this before? Im no professional mechanic but not an amateur either. Im going to try and post a couple pic of the command center. Thanks in advance for any help.

Tx Jim · May 7, 2019

Welcome to TBN
Have you asked a JD dealer service manager for assistance? Way back('74-'87) when I served as a JD dealer service manager JD had a service called D-TAC that service manager could pose service related questions to & get possible solutions. My WAG is a faulty fan control relay or relay getting electrical power when it shouldn't. You could try removing fuse or circuit breaker 1 at a time to isolate the problem.

Lynn Ross · May 10, 2019

We solved the problem. I figured I neede to post the solution as it might save someone some time in the future. We found no no problems with any ot the cab wiring so we started unplugging control modules. The one under the roof cap labeled EPM was not the problem. We got to the one labled EPM-HP located under the rear glass(that had been busted for 5 years) unplugged it and BAM, HVAC fan quit running! Turned the key on and all af a sudden all lights worked and the wiper came on..... Long story short water had seeped into the ECM-HP module and corroded the inside causing the problem.

Zebrafive · May 11, 2019

Thanks for updating. The bust rear window must have been a big clue to help you solve the problems.

Kyle_in_Tex · May 26, 2019

Lynn Ross said:
We solved the problem. I figured I neede to post the solution as it might save someone some time in the future. We found no no problems with any ot the cab wiring so we started unplugging control modules. The one under the roof cap labeled EPM was not the problem. We got to the one labled EPM-HP located under the rear glass(that had been busted for 5 years) unplugged it and BAM, HVAC fan quit running! Turned the key on and all af a sudden all lights worked and the wiper came on..... Long story short water had seeped into the ECM-HP module and corroded the inside causing the problem.

thanks for coming back and posting your solution!