York HVAC unit

[kothari]

The YORK rooftop HVAC unit is having two scroll compressor for Air conditioning.In start up both the compressor run,after few minutes the first compressor stops while the second one keeps on running.The second compressor is insufficient to cool down the set temperature.what can be the cause for the first compressor stoppage?:confused:

[paul_h]

hp/lp fault, overload (on contactor), thermal overload (on crankcase or internal to compressor), thermistor fault (discharge temp etc), controller (eg thermostat), or wiring fault. Take your pick, anything could be causing that.

[kothari]

It it is a thermal overload it has to reset the relay,same with the hp/lp pressure switch.How to check the thermistor or thermostat fault?
Thanks

[monkey spanners]

When the first compressor stops has it still got power going to it? If it has and it has stopped then it if off because the internal klixon has tripped. If it hasn't you need to look at the control circuit for the reaon it is stopping. If it has tripped due to over temperature in the compressor it may take a hour or two to reset. if it has tripped because the compressor is pulling too much current it may reset every minute or so. Put an amp probe on the feed to the compressor, check it is pulling the same on all phases (assuming 3 phase unit) compare this to the data on the plate. If it stops and has power going to it, turn off all the power to it, remove the wires to the compressor (make a note of where they go first) and meassure the resistance between the windings, if there is no continuity its off on the klixon. If the compessor is not being overloaded and has a good power supply(not lost phase, dodgy contactor/fuse etc) its time for a new one.
Just a thought if it is a big scroll it may have a thermistor and a module, basically an electonic kixon, and be off on this. In this case it may not go open circuit on the compressor power terminals. Do not megger test (1000v) the thermistor terminals on the compressor as it will break the thermistors. In this case it may be a faulty module (int69?)
If this compressor is the same size as the one that runs ok you could compare the readings from this one to see if anything looks odd.

Jon

[RAVISEKAR]

What Is Ur Model Of The Unit