carrier 50JZ-048-E roof unit

[refcon32]

Does anybody know how the outdoor fan is controlled ?

In cooling mode compressor and outdoor fan working fine.

Then on heating mode the compressor runs away and outdoor fan does not cut in, to the extent that the condenser coil, compressor and pipework ices up. No 24v on coil of outdoor fan contactor from control board when heating, transformer giving said board 24v. Can bring fan on in heat mode by pushing contactor in.
System running on R410A, outside temp of 8deg celcius, indoor 23deg celcius.

[frank]

Is the indoor room getting warm?
With an ambient of 8c it may not need the evap fan on.

[refcon32]

Ye the room is getting warm.
Just concerned about ice on condenser and the compressor for sake of damage.

[frank]

Frost build up on the 'Evaporator' I would consider normal in heating mode but I wouldn't expect frost on the compressor especially on R410a which is a medium temp refrigerant.

[Brian_UK]

Without any pressure/temperature readings all we can do is guess at what may not be wrong.

[refcon32]

It's the condenser that is icing up because condenser fan is not coming on.
Going to return to site to check relay on defrost board, should be NC and opens when defrost operating to switch off condenser fan, maybe this is the reason fan stays off.

[Loops]

Hi Refcon32,

Does this sytem have a 'cold draft prevention \ pre-heat' function in heat mode? ie the indoor fan is held off until a specified coil temp is reached (maybe ~30°C) then the fan starts

Does the indoor fan start straight away in heat mode? ie no pre-heating

If the system does have cold draft prevention and the indoor fan starts straight away I'd suspect the indoor coil sensor is wrongly giving a very high reading to the indoor board - this would start the indoor fan with no pre-heat function.

Also I think it would 'dump' the outdoor fan in an attempt to reduce the indoor coil temp - which it falsley thinks is too hot.

Worst cases the compressor maybe held off too.

I've had this a good few times on Toshiba & Sanyo kit over the years (and Carrier are merged with Tosh now so ......)

Let us know what you find eh?

Cheers

Loops

[refcon32]

This is a packaged unit on roof. All the workings are in this e.g indoor and outdoor fans and indoor and outdoor heat exchangers. Then the supply and recirc air is ducted to inside building.
Dont think it has a pre heat function, and the indoor fan does start straight away before compressor comes on, does same in cooling although outdoor fan comes on and off in cooling mode.
Will try to find out if it does or doesn't have a pre heat function.

[buford]

Check out your defrost board, This is where the fan is controlled in heat and cool. Even if the defrost stat was stuck closed there is a 10 minute timer built in that should switch over to heat bringing the od fan on. If the hot gas is going to the indoor coil and still no od fan I would be checking out the defrost board.

[install monkey]

Compressor runs but outdoor fan NC (normally closed) contacts on defrost board open - Check condition of relay on board
does not - Replace if necessary
50JZ 024-048 Single-Package Heat Pumps - Carrier
link for manual

[refcon32]

Compressor runs but outdoor fan NC (normally closed) contacts on defrost board open - Check condition of relay on board
does not - Replace if necessary
50JZ 024-048 Single-Package Heat Pumps - Carrier
link for manual

Fitted new defrost control pcb today with no resolve. Still no outdoor fan on heating mode so all icing up.
There is a control thermister that is 26kohms at 7 deg celcius outside temperature. Trying to find out what temp to resistance should be.
Also a logic board this thermister plugs into and also connects to outdoor fan contractor.
Anybody any ideas.

[Gibbo]

Are you sure its not the defrost thermostat your looking at, it closes at -1.1c and opens at 26.7c can't see anything else on wiring diagram. These are coil temperatures .

[refcon32]

Are you sure its not the defrost thermostat your looking at, it closes at -1.1c and opens at 26.7c can't see anything else on wiring diagram. These are coil temperatures .

The defrost thermostat goes on the defrost board with a double plug. This thermister goes on condensor coil, has two yellow wires and goes on logic board. Unit I am looking at does not have electric heater next to controls, instead it has a motor master 11 control with logic board, transformer and another outdoor fan contractor inside. See if I can work out how to put picture on thread.

[refcon32]

image.jpgimage.jpgControl box, contractors and defrost board at bottom. Picture should be on its side with the 3 contractors on right hand side.

[Gibbo]

Don't you just love the Septics and their wiring

[Gibbo]

Thermistor must be for the motormaster.

[refcon32]

I am thinking the thermisters resistance is ok, 26kohms at 7 deg, comparing with figures on line. Motor master must control outdoor fan. The transformer produces the 24v to the logic board, but then no power from orange and brown wires to second fan contractor. Push contactor in, fan comes on.
The logic board is over £400

[Gibbo]

would have thought outdoor fan not controlled through motor master in heating only in cooling.

[Gibbo]

Wiring diagram for Motor Master 11 shows a relay but can't see one in your photograph of logic board and contactor.

Gibbo

[refcon32]

Wiring diagram for Motor Master 11 shows a relay but can't see one in your photograph of logic board and contactor.

Gibbo

I see relay on wiring diagram, there is not one connected to the motormaster. Poped to site this morning to change to alternate operating mode on motor master logic board, changed jumper wire from reset T1 to reset T2 as manual says to bring on outdoor fan at low ambient. Still not operating. Contactor in motor master2 does not get a close signal / voltage.
no use Carrier not having a technical department when parts are so expensive, to just swap out.

[Gibbo]

How old is this unit ?

[refcon32]

How old is this unit ?

I think it was 2006 running on R410a.

[Gibbo]

The photograph of the motormaster 11 box only shows 2 wires going to the contactor coil (orange and brown) next to logic board there should be 4 wires see note 2 on wiring diagram for motormaster 11 follow the dotted line to see what wires you are missing.

[refcon32]

Right enough Gibbo, more investigation has revealed the unit has been fitted without a low ambient kit, which includes a relay, new contactor and temperature switch, all wired to motormaster 11. So can safely say unit has never been able to run in heat mode from install. Which is what staff in building told me, temporary heating every winter. Put cost to client see if they want.
Thanks for input.

[Gibbo]

Glad to help out. The relay is not part of the kit but has to be purchased seperate if kit is sold seperate to unit sale. Don't ask me why would have thought the septics would include it. If unit is supplied already with a low ambient kit they fit the relay at the factory anyway.

[refcon32]

Glad to help out. The relay is not part of the kit but has to be purchased seperate if kit is sold seperate to unit sale. Don't ask me why would have thought the septics would include it. If unit is supplied already with a low ambient kit they fit the relay at the factory anyway.

The relay does seem to be part of kit, listed as relay, contactor and thermister switch. Carrier parts department say that is all that is required. There is an additional furnace relay if unit has a gas burner apparently. Parts ordered now so it better be right for Carriers sake. L.o.l