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jwasir
08-02-2009, 05:27 AM
Where shall the delay on timer should go -- before compressor contactor or before liq. line solenoid valve??

What should be the setting for the timer in case if it is in series with compressor contactor, especially for scroll compressors?

Thanks in advance!

WINJA
08-02-2009, 07:23 AM
Where shall the delay on timer should go -- before compressor contactor or before liq. line solenoid valve??

What should be the setting for the timer in case if it is in series with compressor contactor, especially for scroll compressors?

Thanks in advance!
what sort of system is it on? all our scrolls on pump down dont have any delay , we only have them on systems with no llsv like air con with psc start that needs equalisation before starting

Brian_UK
08-02-2009, 06:23 PM
Most of the smaller compressors are rated for maybe ten starts per hour so a delay timer should be fitted into whatever circuit you have for to control the compressor.

Either use the control signal from the thermostat or the coil feed to the compressor start contactor.

Grizzly
08-02-2009, 07:02 PM
Most of the smaller compressors are rated for maybe ten starts per hour so a delay timer should be fitted into whatever circuit you have for to control the compressor.

Either use the control signal from the thermostat or the coil feed to the chiller start contactor.

Thanks for the info Brian.
Never really thought about it that much.
Now I come to think about it. Most controllers have
a delay on restart or anti recycle setting.
Or even as you say a settable amount of starts per hour.
All makes sense now.
:off topic: I drove 40mls to a site once, having been called out to attend a chiller that would not run.
When I got there the duty engineer and myself, went up onto the roof to find said chiller running.:rolleyes:
"what did you do" was my question.
Well "I pressed the start button and when nothing happened I called you out".
" Oh! You never thought to wait the 2 Min's for the anti start timer to time out" said I!
(Prat!!!)
And I drove the 40mls back home. (missed my family barbecue as well) coz it was Sunday afternoon.
Grizzly

chillerman2006
08-02-2009, 09:25 PM
:off topic: I drove 40mls to a site once, having been called out to attend a chiller that would not run.
When I got there the duty engineer and myself, went up onto the roof to find said chiller running.:rolleyes:
"what did you do" was my question.
Well "I pressed the start button and when nothing happened I called you out".
" Oh! You never thought to wait the 2 Min's for the anti start timer to time out" said I!
(Prat!!!)
And I drove the 40mls back home. (missed my family barbecue as well) coz it was Sunday afternoon.
Grizzly

Grizzly

Used to do alot of transport years ago & you would not believe the amount of call outs i have attended where they say the unit will not run.

Get there & find the unit switched to standby mode (electric) instead of road (diesel)

Never complained though as always booked minimum of 4 hours and often did less than 2 with travel. :D

Grizzly
08-02-2009, 10:30 PM
Never complained though as always booked minimum of 4 hours and often did less than 2 with travel. :D
You weren't working for my company then!
To be fair they have just introduced the 4hr minimum call out.
Trouble is covering Somerset, Devon and Cornwall means that you often exceed this.
Just in travel time alone.
Grizzly

Brian_UK
08-02-2009, 11:36 PM
It amzes me sometimes with "modern" equipment and the fact that the compressor is not protected in this fashion.

Have a site with Denco close control units and in a short space of time it lost two compressors.

The electronic controls are the sort that ramp up a control signal in percentages and when it reaches say 60% it send a go signal to the compressor.

Trouble is being a ramping signal it can also ramp downwards, which these tend to do. Drops to 58% and switches off the compressor. 30 seconds later it hits 60% and away it goes again.
Simple task to fit some start delay timers into the compressor circuit with a six minute delay. No cooked compressors any more.

But why didn't the manufacturers fit them in the first place ?

jwasir
09-02-2009, 03:52 AM
Sorry Guys!

My Question still stays, where shall the delay on timer should go -- before compressor contactor or before liq. line solenoid valve.

I've seen that if soln stays open and timer delays the compr start, liquid sits on the head and try to break the comp, at start-up.

Also, if delay is long, scrolls try to move slowly, when ref passes thru it...

K.R.Iyer
09-02-2009, 09:00 PM
Jwasir,

If your system does not have a pumpdown cycle and you are simply switching off the liquid line solenoid and compressor whenever the thermostat setting is satisfied: In this case, the delay timer can energise both the compressor and liquid solenoid together, say after 3 minutes - when the thermostat reset point is reached.

If you have pumpdown logic, take care of too much cycling of compressor on LP cutout and oil loss from compressor. The energising logic of compressor & sol valve on delay timer could remain same

Denco Technical
09-04-2010, 10:58 AM
It amzes me sometimes with "modern" equipment and the fact that the compressor is not protected in this fashion.

Have a site with Denco close control units and in a short space of time it lost two compressors.

The electronic controls are the sort that ramp up a control signal in percentages and when it reaches say 60% it send a go signal to the compressor.

Trouble is being a ramping signal it can also ramp downwards, which these tend to do. Drops to 58% and switches off the compressor. 30 seconds later it hits 60% and away it goes again.
Simple task to fit some start delay timers into the compressor circuit with a six minute delay. No cooked compressors any more.

But why didn't the manufacturers fit them in the first place ?


Just out of interest how modern is you equipment, our latest controller has a 6 min delay to stop short cycling.

This controller has been used for the last 4 years.

Rob