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LG AHU lv420hhv ducted heat pump air handler odd behavior

Teemok Member, Email Confirmation Posts: 511
This is not a question. I'm posting so someone might be able to identify and resolved the issue I was confronted with. This is a new single zone duct-ed LG red 3.5 ton heat pump. The split system works very well. Aside from the difficult to reach tech support help experience and the wifi connecting learning curve bumps, I'd say it's great. The customer is thrilled with it and the ducting improvement and sealing up done at install. This is installed in a vacation home and is left off until there's a preemptive LG thinQ app use that turns it on to warm up the house before arrival.

6 mouths later I get a bit of a rant call from my customer about how he found the house at 84F when he arrived. He had forgot to turn it on preemptively and was expecting to find a cold house. There was a power outage a week or so before and the power cycling made the Lg heat pump turn on and set the heating set point to 84F since. The power bill was evidence of it.

I suspected a user error setting or something. Even considered someone might have been in the house right then and left it on. Nope, it was repeatable. I thought I must have left a dip switch in the wrong position. Nope, they were all correct. App related? Nope, I isolated the wifi and it still happens.

I power the unit off at the LG simple wired thermostat. I turn power off at the breaker wait 30 sec. and turn the breaker back on. The unit turns on to heating set at 84F.

I found the fault was a larger than dip switch setting on the AHU ducted unit's control board. Well more accurately, a sub board. The addressing board that interfaces a standard RWGYC to the main PCB board. On the sub board there's a 3 position switch. Non-volt, Volt and Not used. I don't know if the AHU comes in the default Volt position so it's ready for a standard thermostat or if I changed it during the install. Changing it from Volt to Not used resolved the odd behavior.


  • GGross
    GGross Member Posts: 1,072
    I thought you were supposed to disconnect the PCB from that sub-board for using an LG controller. Selecting "not used" may achieve the same function, it has been awhile since I dealt with this issue

  • Teemok
    Teemok Member, Email Confirmation Posts: 511
    @GGross I think you're correct. With instructions evidence and all :# That confirms what I suspected. It comes from the factory set up for standard non LG thermostat control and you have to alter it to use their own wired thermostat. Learned the hard way. It was my first LG AHU install. I find LG's English instructions a bit clumsy. It's odd that heat on 84F is a failure mode.