This post is another follow-up on my earlier post regarding excessive energy use by one of my Mitsubishi heat pumps.

Several times in the past I have reached out to Dana Fischer, Director Regulatory Strategy for Mitsubishi Electric, U.S. He has been very helpful in helping me understand the performance of my Mitsubishi mini-splits. Here is what he had to say about the changes between the older model FH compressor and the newer FS series.

“It is true that a jumper was incorporated into the FS series to allow activation of the compressor heater function where desired but by default reduce oil temperature maintenance to lower energy consumption during standby. Ironically, there are contractors who clip the jumper and turn this function on during installation of FS systems to prevent any risk of compressors having a cold start up if the occupant turns off the system for an extended period during extreme cold then cranks the heat pump on and up while the oil is very viscous. $15 is pretty cheap insurance on a compressor if consumer usage might be intermittent during extreme winter.”

Dana went on to say that that “…. the risk [incompressor damage] is low otherwise the change in default from FH to FS would not have been allowed. Durability and reliability take precedent. I don’t have the jumper clipped on my (2) FS12 units that provide me with all my heat or lose any sleep.”

Meanwhile, I ran my data by Marc Rosenbaum, and he indicated that he has the same issue with his ducted Fujitsu heat pump. He says he eliminates this excess energy by shutting off the breaker to his heat pump during the summer, since he never uses air-conditioning.

All, in all, I am very happy with my Mitsubishi mini-split units. Now that I understand the origin of the power spikes in my one unit I can live with the extra $15 per year of electric use.