l'unite hermetique

Hello guys, need help, brain frozen!
Installing a replacement l'unite FH4518 HR condensing unit to an old Hubbard condensing unit for a cellar cooler. Unfortunately the modern day version of the FH4518 is not the same as the one I have removed from the Hubbard housing. The new condensing unit has come with a lp/hp combo fitted with 3 wires, the old one had separate controls. The problem is although the unit has pre-fitted controls, it is not pre-wired, the only thing that is wired is the compressor. All the other wiring - fan,lp/hp,crankcase heater is just randomly attached to the terminal block,needing additional wiring, is this normal for these? The wiring diagram that came with it only covers the compressor.
It got to about half past seven this evening and my brain just gave up, had to walk away. Could any of you guys help me out with how to wire it?
The hubbard unit is a hcu 160, the l'unite is a FH4518 HR. I'll look at it tomorrow and probably suss it straight away, but there's too much going on in me head at the mo.
Any help greatly appreciated

Andy

That is normal for these, just think for a second, what wires are coming from the control panel in the cellar?

You will have the compressor supply, (live and neutral), and a control in and control out as well as an earth.

The comp live and neutral from the cellar go to the terminals which feed the relay, the condenser fan motor can go on the same ones (as you need the fan to run with the compressor) and they rarely run a dedicated pair for the fan from the cellar, and the 2 control wires go to the pressure switch.

The pressure switch will have a common, make on rise and break on rise, you need to use the common obviously and the make on rise, on a Ranco switch it is the 2 terminals closest to the front of the switch, the back terminal would be to energise an HP trip light.

You will of course have a means of isolation to the condensing unit as well in the way of an isolator or a switch to brek the control circuit.

Sometimes you have to run another wire to feed the crank case heater, if it is wired in conduit fairly easy, if not you may need to run another 3 core cable from the panel to the unit.

I hope you can understand what I am saying, I can do it quicker than I can explain it.

If in doubt of the pressure switch, put a multi meter across the terminals and energise the LP side with nitrogen to lift the switch.

Good luck.

Thanks Andy, I'll see how I get on

Cheers

Andy AC

Thanks again for your help, Andy, after having a fresh look at it again this morning, it was blooming obvious what I should of done last night! System up and running in minutes.

Cheers

Andy

Well done mate, sometimes you can get a mental block, it happens to us all.