Crankcase heaters?

[monkey spanners]

Hi,

Found a dead 1 5/8 Hp ACC/Electrolux comp (startwinding beggered) on a self service counter in a restaurant, the condensing unit is sited on the roof above the counter.
The counter has two evaporators which are controled independently by solenoids/stats, and is only run for a few hours at set times during the day when they are serving food, so is off most of the time.
The system is only about two years old and is on its second compressor:eek:
System is on R404A and is on pumpdown control, through the LP switch with no contactor/overloads:(, two discarded LP switch covers show they don' last too long either! The LP was set to 15psi cut in and the same for the diff....

I'm going to recomend that contactors, overloads and an anti cycle timer are fitted.

Now to the main question although opinions on the above are welcome:)
These compressors are not supplied with crankcase heaters as standard, i've fitted one of those orange velcro ones on the new comp run off the changeover contact in the LP, do you think this is necessary?

Jon

[Gary]

Hi,
The counter has two evaporators which are controled independently by solenoids/stats...

This sounds like a recipe for disaster. One stat will shut off an evaporator, leaving the other evaporator activated. The compressor now being grossly oversized for the single evaporator, the suction pressure drops and the compressor short cycles on the LP control with the solenoid still open.

[Springbok]

Hey monkey spanners.:D Crappy call to get now that you're stuck to re-design the system,but someone has to do it.

I would fit the crankcase heater so it stays on during the "compressor off time",seeing the cold winters are harsh in the UK.

It still leaves behind the same problem Gary mentioned,which is logic.Maybe try and cut out the extra sol/stat??:)Good luck buddy....

[taz24]

Hi,
Now to the main question although opinions on the above are welcome:)
These compressors are not supplied with crankcase heaters as standard, i've fitted one of those orange velcro ones on the new comp run off the changeover contact in the LP, do you think this is necessary?

Jon


I don't think it will do any harm to add the heater.

Cheers taz.

[Chunk]

I dont know why people stick these poxy units outside especially in these climates.It cant hurt putting a heater on it,but sticking it in some sort of housing wouldnt hurt either.

I dont see how a contactor would help though,the way i see it is that if you have two coils on it,it is going to be running a lot longer than having one,so starting and stopping is not an issue unless it is majorley oversized.

If i read right and you said it is off most of the time,i take it that it is being switched off and having to start under heavy load?I doubt if they wait for it to pump down then switch it off.This sounds like a problem to me.Can they leave it on even when they dont use it?

I have two similar systems like this and as long as they are left alone they work ok.

[monkey spanners]

Gary, I think that is what has been happening, with the lp cut in and diff set so low its been on and off too frequently.

The counter is 30' or so long and has six evaporators, two at each ends and two in the middle with three condensing units on the roof. The chilled sections are hexagonal divided into two wells, hence two evaporators, into which food 'bins' are placed.
Each well is individually controlled.
Inbetween the three chilled sections are the two heated sections, its all granite and mirrors and must have cost a fortune. Its a shame that some of that money wasn't spent on a design that would provide years of trouble free service.

I'm back out there monday to replace the compressor on the system on the other end as its shorted to earth:rolleyes: The facilities manager is back then too so hopefully i can voice my concerns about the design and installation of the system (who joins pipe by flaring one piece and brazing into the flared bit:confused:)

Springbok, I think you are right, it wants to be both evaps on or none.

Taz, yeah, i though by the time its been off for 10 hours overnight the comp will be stone cold so a heater would be a good idea.

Chunky, the Lp switches are only rated at 16A resistive and they are running the current for the 1 5/8 hp compressor and fan through them, which is why i though a contactor would be a good idea. When they turn it off it only cuts the power to the stat, the condensing unit has a permanent live feed through the Lp. Units are in little metal housings.

I also though a time delay on starting would be good as after three or four minutes the other evap would also be calling for cooling. But its one of those " i wouldn't start from here" things. Best of a bad job...

Cheers Jon

[Temprite]

Lp setting sounds too low could cause short cycling with only one evap running.

You could fit a surge drum to the suction side at little cost and this would slow down the short cycling considerably and you would still get cooling on demand straight away.

Having a timer will disable cooling until time period is reached and may affect temps slightly.

[The MG Pony]

I'd go with your thought of fixing the power first, set LPs on a contractor with any short cycle timer, Now the control side is don start your attention to what other glaring errors are in the design.

Burnt contacts of a LP switch can kill a comp in short order due to lack of current during start up, so with the addition of the contractor and over loads may well do some thing to keep it running.

[Electrocoolman]

Hi Monkey Spanners,

Yes, I would go with crankcase heaters..all the decent outdoor condensing units have them (eg. Silensys etc)...run them from the NC contact on the contactor that you also need to fit.

Assume that shop is single phase...? So If you are fitting overloads then don't forget to loop the current through all three poles of the 3 pole overload.

You'll need to ensure that all three compressors don't try and start together so delay timers would be a good thing.

Are we also to assume that each compressor serves 2 evaps and thus only serves one 'well'.? and so is controlled by its own 'stat and defrost (or controller) which switches the solenoid valve.

Have you ever looked at the CROUZET MILLENIUM controllers....they're brilliant and have logic, timers and timeclock functions all built in. Software very cheap (even free if you talk to rep nicely)...develop and test on your PC then download to unit and it works! You can monitor and adjust in real time. Best to buy starter kit as it includes software, cable and controller.

Could work out cheaper than buying separate timers, and plus you can monitor / control all three systems so that no two try and start together. Could also handle alarm from the overloads.

[Electrocoolman]

Any news or update?

[philfridge]

Hi , fitting a crankcase heater may help keep the oil warm on a frosty night and aid start up in the morning. I think the system with 2 evaps on solenoids / stats is a perfectly normal control ,but your lp control switch is set incorrectly causing short cycling. Cut in pressure 25 psi and 25 diff at least .

[monkey spanners]

Hi guys,

Well i fitted the other compressor, cch and burn out drier. This second system smelt of that blue Leaklock stuff and when i undid the suction rotalock valve someone had gummed it up with Leaklock.

When the maintenance guy turned up i got the impression that he would not have spent the money on the new compressors, and the recommend changes fell on deaf ears:rolleyes:
They started talking about order numbers etc etc before they'll pay and that it could take weeks to get one:confused:, so i think i'll get my money and be too busy if they call again.

Jon

[kiwireeferman]

Geez I thought the life of an Electrolux compressor was about 12 months.