Carrier Supra 750Mt

[Daltonreefers]

please assist,

carrier unit not cooling, the reeon is short cycling through the hot gas system,
MHV valve only gets 12V power for a few seconds before startup then no power at all?

[mattym]

supra should start up in heat but will only do this for a few seconds does the system have enough refrigerant, and are all the solenoid valves which should be open, open and is there any fault codes showing on the cab controller.

[Daltonreefers]

Hi Mattym,
the system is full of refrigerant we weighted the amount to be sure,
not sure what solenoids should be open and what should be closed no manual, this unit starts in heat and remains in heat but on the mother board i see that the relay for cool is on the heat relay is off,

any idea where i could get my hands on a manual?

thanks for your help if you have any other info please send,

[Robert Hilton]

Carrier use a red ring to identify NO (normally open) solenoid valves and no ring for NC (normally closed).

[mattym]

after the unit has started in heat it should swap over to cool after so long, are there any fault codes on the cab command

[Edvin]

What does the CAB command arrow show that the unit is cooling or heating? If You remove the side cover(relay board side), you'll see solenoid valve with solenoid on it and red ring - in cooling mode should not be powered( infact non of solenoids you'll see there should be powered). But since it is a mt the unit has solenoids on inlets of the evaporators, non of them are normaly opened the solenoid before TXV should be powered. Check all off this. Hope this helps.

[moggy66]

What are the Box temps and pressures when unit is running?

[Daltonreefers]

Hi All,

sorry for the late reply, have been working away,
still with problems on this unit the relays are off for heat, also this valve on the discharge side behind the elec box we have replaced, this has been replaced because we found the diaphragm/plunger inside with a hole in it big hole not the hole for ballance pressure! on the cab display the arrow is down cooling,
ambent about 24'C unit set to minus 18'C,
we have replaced the condenser of this unit as it was in a bad condition and after this unit worked sweet for about 5 days, now this problem it iwll not cool, could it be the one way valve is blocked and causing too miuch back pressure on the hot gas valves?

[mozza]

Does unit shut down on high pressure some times condensor closing valve sticks shut which would pressurise hot gas valve. Also run unit with magnet on LV valve in evaporators.

[Daltonreefers]

Hi Guys,

thanks for your help I managed to find the problem,
both hot gas valves had the difram inside damaged (burnt)
I have swaped them with the difram of the discharge line to the expansion valve to test the unit and it worked great,

thanks for your help you managed to put me in the correct direction,
if you are ever in Malta I will buy you a pint,

[Robert Hilton]

I was informed by my local dealer that it is a common fault at the moment. There is an improved replacement available.

[perthtech]

Your correct, this is a very common problem with Supra 850, 950, and Supra mt here in Australia,( only the newish units, with main heat valves, the older Supra's with the traditional 3 way valve was better.) the diaphram distorts, i am sure Carrier released bulletin about it.

[tony2009]

The bulletin is AFS26/09QIA....