my book for this unit does not show an error code "H". Are you sure about the serial numbers and model number? What happens if he tech disconnects the wires for the brush wear indicators?
In the New A/C versions of this truck, an "H" is most often an error code that relates to the hydraulic levers not being at 'zero' when the truck is first turned on. for that reason, the first thing I would check is to see if any of the switches for the hydraulic control valve are "made" (closed contact) when at rest.