control wiring confussion

[FEISTY]

Existing refrig. system comprised of condenser in use with emer. failure back-up condenser in place for small walk-in cooler. Currently indoor units. New outdoor units in place for upgrade. Need advice on switching control system wiring and whatever controls needed. Sys"A" runs and fails. Sys"B" must cycle on and take over. Using common piping run. How should I determine failure so Sys"A" becomes offline and Sys"B" takes over within short time span? Condensers 208V-3ph. Have 120v line pulled to roof if controls need to be connected at units. This one stumps me since 3 other companies previously wired orig. system . Pure unmarked spagetti !!! Thanks. Jeffrey5151.

[nike123]

Few relays and one thermostat should make the job.
Failure is determined by this sequence.
First when system A reach set temperature, one control relay go in on position and memorize it, then when added thermostat (error sensing) thermostat reach set temperature (one or two degree above regulating point on system) second relay goes in on position and memorize it. That is signal who activate system B, alarm, and disconnects system A from power supply. Than system B carry on until system A is fixed. By reseting relays we established normal operation of System A.
That would be one of my solutions. It could be done different way, but this is first what is on my mind reading your description.

[Tesla]

You need status of differential temps across evap to prove weather cooling is taking place or not, via tstats or controller to activate alarm and enable cooling from backup system. Also under high ambiant/load the alarm could be disabled and second unit enabled to run if there are two seperate units serving one common space

[hendry]

yes, adding few relays would do the job.

1] tap failure signal/s from System #A;
2] connect this failure signal as startup signal/s to system #B;
3] check the voltage of various devices i.e. AC or DC, 24V or 230V etc;


* you could assume the failure signal from #A as the action of pressing start button for #B.

hope that helps.

[Airmechanical]

Existing refrig. system comprised of condenser in use with emer. failure back-up condenser in place for small walk-in cooler. Currently indoor units. New outdoor units in place for upgrade. Need advice on switching control system wiring and whatever controls needed. Sys"A" runs and fails. Sys"B" must cycle on and take over. Using common piping run. How should I determine failure so Sys"A" becomes offline and Sys"B" takes over within short time span? Condensers 208V-3ph. Have 120v line pulled to roof if controls need to be connected at units. This one stumps me since 3 other companies previously wired orig. system . Pure unmarked spagetti !!! Thanks. Jeffrey5151.

why dont you wire a second temp. controller on it, then when the primary

condenser fails and temp goes up to the setpoint on the second controller

the second stage (redundant sytem) (secondary system) fires up!

run everything through a 90-340 relay, only one or the other

condenser can run at any given time!



.

[Kh1971]

very simple , just connect to the thermostat and then once the first system well not work the standby well start since it is ready for work. i hope I help