Air conditioning

[balaji]

Hi,
Can anybody clear my doubt pls
I believe that when the room attains the set temperature the thermostat will de energise the liquid line solenoid valve so that the the compressor will cut off through low pressure switch

My doubt is if the compressor cut off in LP switch then how it will restart again when the room temperature starts increasing

i heard that if the unit trips through LP switch, without resetting we cannot start the unit

can anybody brief me how the cycle is controlled ill be thankful to you because iam weak in controls and i feel difficult to understand the control circuits

regards,
Balaji

[nike123]

That depend on LP switch and used controller settings.
You could have Lp switch with manual or automatic reset.
You could also have control that needs manual resetting and other one that is automatically reset few times and after that you need manual reset.

In case when pump down circuit is used (like your example) Lp switch is automatically reset.

[balaji]

Hi nike,
Thanks for your reply. i want to develop my knowledge in control circuits is there any reference book, if you have please forward to me. except you nobody reply to this thread why? I asked silly questions ?
regards,
Balaji

[malik55]

A question is a question,
AND IT IS BETTER TO ASK THEN NOT TO ASK....
What you asked is a pump down type system and when temperature satisfied the thermostat cuts solinoid and system stops by L.P, Normally this type of systems works with two L.P switches, One for the Pump down and second one for SAFETY CUT OUT, The second L.P swith set point is much lower then pump down L.P.

[nike123]

I asked silly questions ?
regards,
Balaji

Check my signature!

[nike123]

Hi nike,
Thanks for your reply. i want to develop my knowledge in control circuits is there any reference book, if you have please forward to me.

No, I don't have any book.
Most of required knowledge you could gather by reading service manuals of equipment.

[nike123]

A question is a question,
AND IT IS BETTER TO ASK THEN NOT TO ASK....
What you asked is a pump down type system and when temperature satisfied the thermostat cuts solinoid and system stops by L.P, Normally this type of systems works with two L.P switches, One for the Pump down and second one for SAFETY CUT OUT, The second L.P swith set point is much lower then pump down L.P.

To add to that, Pump down LP switch is automatically reset type and safety cut out switch is manually reset type.

[Mozambezi]

Nike, check the posters signature name... and relax.

To Balaji... try to use screwdriver for LP adjustment. It helps to understand how switch works.

[brunstar]

balagi, i could see the use of this type of control on a refrigeration plant but it will not cut out on low pressure as such just a differential pressure, if you had a system cutting out like this everytime it reached thermostat i can't see it being good for the compressor.

[balaji]

Thank you guys atleast i received 8 replies, iam satisfied and i hope no need to go for two LP switch even a single LP with three set points can do that

[R. skiffington]

Balaji, This is very straight forward, You are correct in saying that when the thermostat reaches temp it de-energises the solenoid and allows the compressor to pump down then cut out on the LP switch, when the thermostat calls for cooling again, the solenoid opens and, the pressure rises, closing the contacts of the LP switch and the copmpressor will restart. This type of control circuit is not always needed on a chiller but almost always on a freezer. The advantage of this circuit is if there is a great distance between the compressor and Evaporator, you do not need any cables running between as you can locate the Solenoid inside with the Evaporator. Hope this helps.

[malik55]

Different type of controls can do same things, A systems can pump downs by a thermostat and also by a L.P switch.

[Sridhar1312]

Normally LP is auto reset where as the HP will have to be manually reset.