Changing Compressor Low ambient

[lees8110]

Hi All,

I am half way through replacing the compressor on a Lennox AHU Package unit. The unit has been off line for sometime now, I am just wondering how low ambient temperatures will affect the system as I am still fairly new to the trade.

I have vac'd and refilled with ofn several times now to try and rid of any ice/moisture/particles ect



Would it be good practise to leave the crankcase heater on for sometime before starting it up for the first time?

I have no sightglass on the system so will have to weigh the charge in what sort of effect will the low ambient temp have on this?

Sorry for all the questions, im still learning!

[DEVIL]

It depends on how low is inside the unit,and if you had any other problems beside the compressor change.

Typically it is recommended to add some electrical heaters (temporary heat blowers) to heat the entire system, it's not enought only for the crankcase heater (depending on the actual ambient temp), and vac the system at the same time.
if the pipe temperature is too low, you might vac forever and it not extract all of the moisture (depending on the repair that was done).

And obligatory replace the filter dryer in case the unit is having one.
And putting this all beside for the start u need the crankcase heater on for 6-8 hours (i do it for more than 12 hours) for the oil to be heated up.

And for the weight, the refrigerant is having the same weight for any temperature/pressure for the same amount.

wen you are charging the unit, make shore the liquid is not depositing in the compressor

[TRASH101]

Would it be good practise to leave the crankcase heater on for sometime before starting it up for the first time?

It is very good practice to have the crankcase heater on at all times when the comp. is not running (and even sometimes when it is)if the oil ever gets cold you should allow sufficient time for the heater to achieve the oils required standing temperature. Most manufacturers say a flat time of 12 Hrs but the bigger comps could be 24 Hrs+.

Filling by weight (especially on packaged units) is the prefered way.

[lees8110]

Cheers guys, I have changed the drier yes I am just worried there still mite be ice in there as since I started the job its bearly reached above freezing! I will have to source some type of heaters.

The reason I changed the compressor, the previous was taking out the main mcb, a winding was down, before the compressor failed it was making dodgy sounds like moisture was in there.

How long would be advised to vac for while heating?

[DEVIL]

Depends on the size of the unit, and if you can cover it all up with foil or something to keep the heat inside and the temperature you manage to get inside, you might get away with 1-2 hours at 30 deg C, but the unit size is important

[lees8110]

Cheers mate,

Its not too big its a package unit with 7.71kg charge of 407c H.5ft W.4ft L.6ft

[DEVIL]

Then yes , 1-2 hours if you manage to lift the temperate should be enough