Any refrigeration experts here?

ProDave · Apr 30, 2012

Todays job, go to a farm to connect a "chiller"

Well it wasn't quite what I expected. It's the back off an old refrigerated lorry, but not with it's original chiller unit.

The chiller comes in two parts. Inside the van body is a heat exchanger and fan unit, outside is the compressor unit.

It's just been moved here from another farm. Whoever disconnected it just removed the two SWA cables but didn't note how they were wired. and of course no manufacturers name plate, no instructions etc. so it's a case of "work it out"

The inside heat exchanger is simple. The junction box just has 3 terminals, L, N and E, so that has a permenant supply.

It's the compressor unit that has me slightly stumped. It has a 6 core SWA cable.

Cores 1 & 2 connect to the compressor and a fan.

Cores 3 & 4 connect to what appears to be a pressure switch. It has two screw adjusted dials in Bar, and capillary tubes off to parts of the pipework. In it's degassed state, that's showing a closed contact.

Cores 5 & 6 connect to what I think is a solenoid valve on a bit of pipework. That's a Danfoss 018F6177 or BE240AS.

So what I've done for now, is connect 1&2 directly to L & N and fed the solenoid valve via the pressure switch.

That will probably do to get it running for when the man comes to re gas the system later this week.

But how should it be wired?

I'm guessing there was a control box for this, that got left behind. I've asked the farmer if he can find out if there's anything left on the wall at the previous farm.

I'm absolutely sure the compressor should not run all the time but how should it be switched? via a contactor from the pressure switch or what?

I can't see any thermostats, but there are what appear to be temperature probes in the main lorry body connecting to the fan unit, so I guess they turn the fan on and off to regulate the temperature.

Manator · Apr 30, 2012

It has been ages since I worked on any of this type of units, most were mobile units sold second hand to run farmer gyles's farm fridges. From memory I have always had a control panel to regulate the temp, and there was always another probe to go inside the refrigerated area. Other than that useless information I am sorry I can not help you.

ProDave · Apr 30, 2012

Yes that pretty much confirms my theory about a missing control box.

Lets just hope the farmer finds it.

I guess if not, a suitable thermostat (frost thermostat as they go to a lower temperature) switching a contactor to turn both units on and off will have to do.

ProDave · May 1, 2012

Hi Canoe

I only have ONE pressure switch, that shows a closed contact with the unit degassed.

The solenoid valve I have is on the flow (or return I don't know which) line from the compressor box to the heat exchanger box.

So assuming we can't locate the correct control box, what's the easiest way of wiring those to do the correct thing? I assume it's more complcated than switch in series with solenoid that I have at the moment?

Thermostat and contactor is easy to do.

In the fan unit there are what look like strip heater elements running across it. They are wired in parallel with the fan so are on all the time the fan is. sounds a bit wastefull?

so it sounds like a periodic defrost cycle would be to run the fan unit alone without the compressor?

I'll tell the farmer not to run it other than a short test run when the gas is charged, until I can find or make a control box for it.

ProDave · May 1, 2012

I'm not doing the pipework, someone else is re piping the two units together and re gassing the system.

I only need to know how to control it.

The pressure switch has two pipes into it, and tow scales, calibrated in Bar. It only has ONE set of wires coming out of it, so I assume both pressure switches in series, or perhaps parallel, I didn't open it up to see.

Under NO pressure (the system is degassed at the moment) the pressure switch registers a closed contact, so one can reasonably assume the contact opens when one or both of the thing's it's measuring reach the desired pressure.

The solenoid valve is in line as the LAST thing in the compressor box before it goes out to the heat exchanger unit in the van. I don't know if that's the flow or return.

I VERY briefly powered up the compressor, and it blew out of that connection the solenoid valve is in, so that kind of suggests you energise it to BLOCK the flow in the pipe which is not what I was expecting (I wouldn't have powered it if I knew that was the case)

All I'm trying to figure out is how to get it working for them. I'm not trying to re design the pipework.

The heating elements go across from one side to the other of the coil block in the heat exchange unit. I agree, they only need to come on when it's defrosting, but the fact they are wired in parallel with the fan so come on most of the time does not inspire much confidence that it was wired and functioning correctly in it's last installation.