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#30881 11/01/03 05:41 AM
Joined: Jul 2002
Posts: 8,407
Trumpy Offline OP
Member
Guys,
I am after some advice.
I have never been trained as a Refrigeration Engineer, but I have seen a wierd sort of trend, at work.
A farmer will come into the shop and have a Refrig unit at his farm that has to be hooked up to his new 30,000 Litre Milk Vat, I have no problem with the piping, evacuation and charging of these systems and have done this on the odd occasion.
But, the question I have for you guys is:
(just as a note,I have no problems with wiring the Compressor motor and the Condensor fans)
How are the Control circuits associated with these units wired?.
I'm under the impression that Refrig units are more or less universal in thier connection Diagrams?.
Is there anyone at ECN here, that works with Commercial/Industrial Refrigeration Units?. [Linked Image]
Normally all I get is a mess of cut wires and no Control Board or Controls, for that matter!. [Linked Image]
Hey, I'd be really happy if someone could show me how these units are supposed to be wired.
I usually have to wire these things up by Trial and Error, with the emphasis on the latter, but I'm getting better.
Scott35, I can feel a Circuit Diagram in the Technical Reference Area comin' on!. [Linked Image]

#30882 11/01/03 07:51 AM
Joined: Dec 2001
Posts: 300
M
Member
I do alot of cooling and refrigeration work and would be happy to help but I'm nto sure I understand your question: If you've got the condenser fan and compressor right, the rest is just typically the thermostat and the safety controls (high pressure cut out, low pressure cut out, etc) all wired in series with the thermostat to prove everything is working properly.

If any of the safety controls is open (meaning there's a problem) than the compressor and condenser fan contactors don't get energized.

But some systems (here in the US) use 24V for control wiring, some use 120V or 208V. There are also all sorts of controls. If the evaporator coil is directly submerged, you may want to prove the circulating pump is pumping or prove the evap temp so you avoid freez-ups.

If you're in an area that gets cold, your condenser fan may need to cycle on and off with a condenser pressure switch instead of running all the time. (known as a low ambient control)

Most of the time, condenser fans and compressors are energized through contactoras who's coils are energized by the t-stat and 24V transformer with all the safety switches in series with the thermnostat/transformer/contactor coil circuit.

#30883 11/01/03 08:33 AM
Joined: Jul 2002
Posts: 8,407
Trumpy Offline OP
Member
Maintenanceguy,
Hey thanks heaps for your reply.
And sorry about the "up in the air" question.
Your reply has given me a great lot of insight into the workings of this sort of gear, which is something that I have only just started working with, although the company that I work for has been doing Refrigeration work for the last 40 odd years, a few hours of training wouldn't go amiss!.
This job really caught me off-guard, I have a reasonably good knowledge of Electrical systems, but to be thrown in the Deep end and have to wire one of these units, as quickly as possible, just sent me out of my tree!.
Our Control circuits for Refrig units are typically either 400V or 230V AC.
Just not even having a small thing like a basic wiring diagram or not knowing things like the current draw of the compressor (Nameplate was all rusty), made this job twice, probably 10 times harder.
Thanks for your time, bud!. [Linked Image]

#30884 11/01/03 12:50 PM
Joined: Apr 2001
Posts: 507
G
Member
We don't do a lot of refrigeration but do get the opportunity occasionly.

Most of the controls I have seen are 120/208 with the compressor controlled by a pressure switch. The evaporator is controlled by a themostat that switchs the freon solenoid valve and may control the evaporator fans. One compressor can serve several evaporators.

Often these systems are a conglomeration of used equipment. Usually what I do is ask the refrigeration tech. how he want the system to work and then set up the controls to make that happen. Sometimes they want the evap. fans to run continuously, sometimes they cycle with the thermostat.

Often there is no electrical tie between the compressor and evaporator. Defrost timers, heaters etc. are another matter.

These are really very basic control systems but it can get confusing because lack of schematics.

Good luck!

GJ

#30885 11/01/03 09:07 PM
Joined: Dec 2001
Posts: 300
M
Member
If there is an evaporator solenoid present, it's usually to prevent flooding the evaporator during the off cycle.

I've never seen a compressor controlled by a pressure switch. But there are often pressure switches to lock out the compressor if something goes bad.

#30886 11/02/03 01:00 AM
Joined: Oct 2001
Posts: 135
W
Member
It is not uncommon to control the compressor with a preasure control instead of a thermostat on refrigeration equipment.

A larger unit that has a liquid line solenoid and a pump down cycle will use a preasure control to control the compressor.
The liquid line solenoid closes - on temp or preasure - and the unit pumps down and shuts off at 15-20# suction.

[This message has been edited by wolfdog (edited 11-02-2003).]


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