re-wiring Carrier to run from existing controls

[knighty]

we have a carrier system (front of lorry back box type) and all the fancy electronic controls decided to go up in smoke a while back... but we already had a "normal" system fitted to the box anyway (quieter)....

but now it's getting a bit warm I'd like to be able to run the original cooler overnight too (to make sure everything is frozen)

my plan is that.... from my look at the wiring diagrams that came with it, I can just run, internal fans, compressor, then for defrost, the defrost solenoid valve and the compressor again (hot gas defrost) and that's everything working ?

and.... if I just control these using the system we added, I just need 3 wires to the lorry system (internal fans, run, defrost?)

I'm just checking there's nothing else I have to wire up ?

the alternator is dead on it too... but I have a 50amp 12vdc supply there that will run it...

plus... if I run the 3 wires I need through a 3phase switch, so all are connected/disconected.... I can just use that switch to turn the lorry system on/off ?

.... sorry I'm not very good at explaining this.... I could do it perfect in person !

any input / ideas anyone ?

[knighty]

p.s. the questions is, have I missed anything ?

oh and... the unit is from 1995... that's all I know about it, can't find any other numbers.... if you can tell me where to find them I can get them ?

[alpha]

Hi, I'm not too sure that running three wires from the working freezer to the non working Carrier is going to be the best method, I would think that allot of reworking is going to be needed on the transport fridge as I suspect all the control relays are 12vdc for fans,defrost etc. I can also see that getting both units to defrost effectively may be an issue especially if they are working as one, I'm not saying it most certainly can't be done just I can see a better way. Another line of thinking, depending how the evaporators are situated if they are blowing toward each other I suspect you may suffer poor airflow and if the transport fridge has a defrost airswitch it may go onto defrost prematurely, I wouldn't like to speculate really without seeing your setup.

I presume the Carrier is an old diesel unit? a Mistral or a Supra perhaps, you may find an id plate either on the backwall of the unit behind the engine/electric motor, or on the sidewall engine side somewhere, possibly at the point where fuel lines and battery cables connect to the unit itself.

Personally, I think your best bet maybe to mod the Carrier so it works completely off it's own back. If it's never to be run on diesel again I think I'd probably rip all the electrics out of the controlbox and start again for electric operation only, saving all relays and contactor and overload then tying it all together with an electronic defrost thermostat or similar.

Sounds fun, good luck

[knighty]

hiya, thanks for the reply

I'll have a look for the id plate you mentioned and post back

and yeah, I intend to rip out all the old wiring to make it run from electric only...

the (rough) plan is....

1 contactor to power the inside fans
1 contactor to power the compressor to run to cool
1 contactor to power the compressor with one of those piggyback thingies on top of it so it powers the solenoid for the hot gas defrost too

the way i see it, if i power those contactors from the original system fans, compressor, and defrost heater then everything should run ok.... ?

the original unit is at the front, and the extra one we now run is at 90' to it in the middle of the fridge....

I'm not sure about the defrost.... I always thought the hot gas defrost was much better / quicker then an electric one ?

either way, it original unit will only be run overnight on hot days to help freeze everything we've put in there during the day... (its a bit noisy to run during the day!)

thanks

Alan

[chillin out]

Going by what you have said, I would say that you should be OK.

I take it that you are just using it in one place and not transporting it around?

Chillin

[knighty]

yeah, it's off the lorry and used for storage..... at least it better be, the compressor for the system we added is fixed to the side of it

I just wanted to check.... there's nothing else I need to power to make it run ?

[chillin out]

Nope, just a few light bulbs.
And maybe a drain heater, door frame heater.

Chillin

[knighty]

cool

thanks for the help everyone