Fujitsu air-con standby power and sump (crankcase) heater - Page 1
Forum section: electronics / general

author: haxby
author_rank: Contributor
timestamp: February 13, 2015, 01:23:59 am
content: So I have a Fujitsu AOTG30LATL 9kw compressor ducted reverse cycle air conditioner at my house. I have heard that they can consume 150W continuous on standby due to the crankcase heater. The energy saving forum mentions that this figure was found using a watt meter, and I am dubious about the accuracy of it. (sounds very high!)I have the installation manual to the system, however it does not mention the standby power, nor does it mention whether the sump heater is thermostatically controlled or whether it is just on all the time, so I would like to measure it accurately.I have a Fluke 233 multimeter, and was thinking of setting it to the AC current scale, and connecting it in circuit.Now, it is a true RMS meter, but how do these meters go with inductive loads? Can I just multiply by the voltage to get watts?If the crankcase heater runs off the DC inverter power, the power factor could be atrocious at this low power level.

author: BradC
author_rank: Super Contributor
timestamp: February 13, 2015, 01:38:20 am
content: Quote from: haxby on February 13, 2015, 01:23:59 amThere is generally nothing inductive about a crankcase heater. Most often they are a strip heater physically wrapped around the compressor shell. Pop the covers off and have a look.In big industrial compressors they sometimes (rarely) leak a small current through one winding in the motor to keep it warm, but I think I've seen that maybe once.The crank case heater in my (Aussie made) unit draws about 60W but only comes on as the crank case temp drops. I've not bothered to put a thermometer on it to work out the actual temp values but it keeps it "warmish" to the touch. We don't reverse cycle ours, so the whole unit gets switched off at the isolator over winter and just switched on for a day before firing it up as a precaution to let the refrigerant boil out of the oil. It's that initial flood of refrigerant carrying the oil out of the compressor they are trying to prevent.Punch your model into google and you'll probably find a service manual. There are loads of Fuji manuals out there if you have a look. They all have schematics in them.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 13, 2015, 04:02:45 am
content: If it's thermostatically controlled, you can get an insulating jacket to put around the compressor.

author: SeanB
author_rank: Super Contributor
timestamp: February 13, 2015, 04:46:39 am
content: Most crankcase heaters I have seen are a PTC element you place in a socket in the compressor base, with 2 wires leading to the mains supply. They draw 150W when cold, but when it gets to setpoint the draw drops a lot. As here we never have it cold enough to use the units as heat pumps most have them disconnected as ambient is enough to keep the oil warm in any case. Leaving it connected when in use as a heat pump in cold ambient though will help with oil flow.In most cases the compressor will have a jacket around it, made from an outer neoprene rubber with a fibre lining, held with a strip of hook and loop fabric stitched to it. That is common in split units, though I tend to remove them as they cause issues here with corrosion, and trap moisture on the compressor case from the suction side. I always give the compressor a coat of anti rust paint if possible when new before installation, as there are a few places like the suction elbow and the base plate mounts that always rust, and which eventually leak. Have one going in under warranty today, it has leaked from the compressor. First time though that I found the leak not to be the suction flange or the base plate, this one is leaking from the terminal block. Gas sniffer located area then spray confirmed it. Now to evacuate and pull it out to take in.