Single pole contactor & crankcase heater

[herefishy]

Helping out a friend (by GOD, if I'm working on your air conditioner - you're a good friend), I pondered the use of the single pole contactor (with the common bar on the other line). I just learned that the purpose of that congiguration is to complete the circuit through the crankcase heater which is wired across the (open) contact of the contactor, and "disable" the crankcase heater when the contacts are closed.

What amount of heat gain (or increased load) do you anticipate with the crankcase heater energized during compressor operation, in such a case as a two pole contactor be applied, and the heater connected to the line side of the contactor (always energized). ooops!

[frank]

Crankcase heaters are normally around 40 to 60 watts so not much of a heat gain.

We had a compressor go down a couple of months ago and reported it under warranty. The manufacturer admitted that it was a design fault as the crankcase heater was under sized and allowed the oil to be carried out of the crankcase which causing the failure. Seems like you have to be careful with these things.

[Gary]

We had a compressor go down a couple of months ago and reported it under warranty. The manufacturer admitted that it was a design fault as the crankcase heater was under sized and allowed the oil to be carried out of the crankcase which causing the failure. Seems like you have to be careful with these things.

I'm betting the coil was above the compressor and/or the unit was started in cool weather.

[frank]

It was a "plug" type heater Gary which fits into a small aperture in the base of the compressor. The unit in question was a Daikin VRV Plus system which comprises of 3 outdoor condensing units (6 compressors).

This link will show more http://global.daikin.com/global/our_...rv/p_vrv.html.

The system is a 24hp unit, 3 pipe heat recovery with one inverter driven compressor and 5 on/off units. The unit that failed was compressor No. 6 - the last to be called so you can see that it stood there for most of the time at rest just collecting liquid.

Apparently, upgrading to a 60W heater from a 40W heater has done the trick.

[Sridhar1312]

Some of the scroll compressors I have seen are without crank case heaters can any one tell me Why?

[monkey spanners]

Some systems pass a small current through the motor windings when the compressor is off, just enough to keep it warm, so don't need a crankcase heater, some are on pumpdown, and some should have one fitted and don't....

[NoNickName]

Crankcase heaters are to be considered as "COMPULSORY" . Monkey spanners: I don't know where you heard about that story of current leakage, but it makes me smile, also because motors are not in the oil, and it's not the motor who has got to be warm, but the oil is!
Additionally, heaters can burn when kept ON while compressor is operating, because heaters could be overheated and burn out. That's why they always have to be interfaced with a NC contact of the compressor contactor.

[NoNickName]

Some of the scroll compressors I have seen are without crank case heaters can any one tell me Why?

Because the installer forgot to buy the heater or just wanted to speculate for few bucks.