Just want to share how I fixed the problem of a weak fan of my "HRV" branded positive pressure ventilation system. I have a system with two galvanized fan/filter system boxes, i.e. a master and a slave unit. Model 'Arizona Janus Phoenix Rango'.

I noticed that the air flow out of the ceiling vents supplied by the slave unit had become a lot weaker than in the rooms supplied by the master unit. Both fans were still running, but one was just a lot weaker than the other.

First I used a plug-in power meter (from Wellington City library) to compare the power consumption (Watts) of each of the units, e.g. when running on full ('burnt toast mode'). The power use of the slave unit was only about 80% of the master unit, at the same control panel setting and fan speed indicator level. This confirmed that it wasn't just an unevenly clogged filter, or leak in the ducting.

The fix was replacing the fan motor run capacitor in the slave unit. When you open the fan box (as if you were replacing the filter), look up inside. The capacitor is the small cylindrical component that is mounted below the fan, and connected to the fan motor wiring. Took a photo of the capacitor specs written on the capacitor, then ordered an equivalent capacitor from rs-components. Cost about $15 plus shipping.

Took about 20 min to install. Now the power consumption of the master and slave units is about the same, and so is the air flow coming out of the ceiling vents.

Make sure you unplug the power supply to the HRV system before opening the unit so you don't zap yourself.

Sharing this as I initially spent a lot of time fiddling with the settings of the controller, to no avail. Hope someone will find this useful.