When we built our house we installed as the main HVAC, in Finnish, a Poistoilmalämpöpumput (PILP). Whether that was the most efficient thing to do over that time is a good question, but it is now nearing its twentieth year with only a few hiccups. Those include filling the air exchange unit with water that destroyed the output air fan as well as a couple of electrical condensers being replaced. The timing of these episodes has always been impeccable, so it was of course right on New Year’s Day that the unit started making a noise audible right through the house.
Twenty years is quite well beyond the expected lifespan for a system like this so it was slightly relieving to find it seemed to be only the input fan, but calling out someone under any circumstances is expensive and takes time. It occurred to me to just replace the fan myself since is an easily accessible unit with a simple connector. A few hours of searching made me doubt that. The model of PILP we have is a Nibe Fighter 410P and it seems that although the model was sold for multiple years the components in it have changed. The fans alone have moved from AC to DC over the years and even within the AC type fans the manufacturer has changed. The original model in ours from 2004 is a Swedish Östberg model RFE 140 DUU S2. These don’t exist any longer and although there are generic ventilation system fans with similar size and specs whether those could be a drop-in replacement isn’t clear. In some forums it was implied that they require different control electronics to work. An AC fan apparently requires a controller to ensure it spins in the required direction. The replacement fans price ranged from 150 – 350€, so a mistake is expensive. But calling a repair person to visit is easily another 200€ on top of that.
From the forum investigations I learned that the only thing that fails in the fans are the bearings and those bearings are technically replaceable. Some versions of the owners manual even instruct how to do this. So, if it was failing anyway then pulling it apart couldn’t really make it that much worse. After translating 10 – 15 year old Finnish forum posts I did some double checking of the fan and then went shopping.
Firstly, the bearings themselves are hidden by a plastic plug over the main motor shaft. You remove the plug by jamming a sharp object down the side and levering it out. That exposes the bearing which turns out to be a 608Z ABE C5. Luckily Biltema has exactly this available for 7,40€ each.
The next issue is that there are two bearings, one exposed under the plug and one at the other end of the shaft. After removing the retaining clip off the shaft and some washers next use something and a hammer to tap the shaft and drop it out of the top bearing.
This frees the shaft and motor enclosure and exposes the second bearing. This one is bonded to the shaft by age and will not come out. This requires a bearing removal tool which I also bought from Biltema based on my forum reading. Except that the one I got is far too big to fit inside the motor enclosure and also has too fat feet to slip under the bearing. After some contemplation and swearing there was another trip to Motonet for a different model of the puller tool. Of course not having taken exact measurements I just had to pick something that looks like it would fit and have feet that would slip under the bearing. This one was nearly 40€ or 4x the price of the wrong one from Biltema. And of course when I got home and tried with the new one it also didn’t fit in to the housing. Well almost didn’t fit, since with some creative usage it was possible to get the bearing to move enough to use the puller as intended and get it finally off the shaft. The replacement just slipped back in.
The first bearing was free of the shaft already, but jammed into the motor housing. Getting it out required creative use of a screwdriver and hammer. Luckily the bearing is slightly smaller than the size of the hole through the motor where the shaft goes, meaning you can wedge something against it from inside the motor and tap on it to free it from the housing. The replacement also goes back in with a few taps to seat it fully.
The only thing remaining is to put everything back together, the shaft back in place, and the washers, retainer and plug. Then mount the fan back into its duct, and then install the whole unit back in place. When I finally switched the Nibe back on it made it normal startup racket and the fans started spinning and made a terrible grinding noise. After a momentary panic I realised it isn’t the fan, but something else entirely.
Next to the fan is a solenoid that holds open a door on the air channel while the unit is on. Obviously when the unit is off it blocks the channel and prevents back flow of air from the house. That is connected via a spring loaded arm through the wall of the fan unit mounting. That arm vibrates against the sheet steel wall and makes a racket. Holding the arm just right silences it, but nothing I can do stops it vibrating except by holding it. As it happens there was a small kitchen sponge handy and jamming it against the arm stops the vibration completely. This brought on some serious déjà vu, but I have no idea what the solution was previously.
The end result is the normal amount of noise with near silent fans again and at a cost of 60€. The biggest concern now is that how long can we get away with this. The service guy we used previously already warned that something more serious like fixing a compressor failure would be not worth the investment. A replacement HVAC system is likely to be close to 20000€.
