Toshiba RAV SM/SP1400 defrost problem

[SteinarN]

I have a problem vith a Toshiba RAV SP1400 heat pump.

When the unit is in heat mode all seems to be ok. But the problem is with the defrost on the outdor unit. The pump goes in defrost with or without frost on the evaporator. The outdor fan and compressor stop. 4-way valve go in defrost. Then stay in defrost for roughly 2 min acording to the symbol on the wired controller. The compressor may start during these 2 minutes. Then shifting to heat and operate normal without any ice melting due to short time in defrost. TCE sensor is ok. (defrost controlling probe) TCE probe at 0 degres when shifting to heat. Maybe -3 before skifting to defrost. Go in heat for maybe 15 min. Then shift to defrost again!!
And all repeat.

All temp sensor is ok and gives normal readings. Heat capasity is exelent as long as the evaporator doesnt get full of ice.

My only guess is the clock going crazy. There is 10 min max alowed defrost time. I also think it will defrost after some hours in heat mode regardles of any ice on evaporator. Is it possible the clock is running at 5 times the normal speed? Have any experienced this problem before?

Any help much appreciated.

[nike123]

Does during defrost you measured pressures and temperatures of refrigerant circuit?
Does unit displays any error code in indoor unit during defrost?
I would also change defrost sensor.

[SteinarN]

No errorcode whatsoever. Havent measured any pressure. Sometimes the compressor doesnt start up at all while in defrost. When it does, defrost seems to be ok as long as it stay in defrost. The problem is it doesnt stay long enough in defrost. Defrost sensor is the TCE sensor. This sensor seems to give normal readings when i monitor that sensor during heat and defrost mode. (its located at the very inlet of the evaporator) Its roughly 5 degres below ambient in heat mode.

[The Viking]

Steinar,

Have you got the service manual?

If so, the defrost operation is described on pg 112.
If not, let me know and I will get it to you.

BTW, How cold is it outside where you live now?

[nike123]

Does that unit have electrical heater for drain pan defrost in outdoor unit? Is it possible that that heater have influence on TCE sensor (in service manual it is called TE sensor).

Defrost is controlled with TE sensor and time. Time is function of PCB.

Possible cause is faulty sensor, his location, connection wires and PCB.
I would start, as I earlier said, with changing sensor.

[superswill]

faulty outdoor PCB?

[SteinarN]

I'm impressed!

I got a mild attack of alzheimer, hopefully incidentally, i ment TE sensor.

Yes, i have the manual.

Heater is installed and vorking. No ice in the drain pan. I installed the heater, its nowhere near the TE sensor.

The TE sensor is showing lets say -4, then defrost, then TE raises to 0 in rougly 30-60 sec, compressor may or may not start, after rughly 2-3 min then compressor and fan starts in normal heat operation. The point is TE should raise to 12 degres before end of defrost!

When the unit has been off for a long time and then is switched on, all the sensors in the outside unit show the same temp. No reason to believe any of them is defective.

[The Viking]

Then, until one of the Tosh guys get a chance to reply, my answer would be to replace the outdoor PCB, as suggested by Paul above.

[nike123]

Then read this thread!
http://tinyurl.com/227p9e

[SteinarN]

Thank you for your advice. I'll get new PCB boards.

One more question. It's the indoor unit PCB board which is controlling the unit and probably the defrost also. Then it's probably the indoor unit PCB board which is faulty?

[nike123]

Thank you for your advice. I'll get new PCB boards.

One more question. It's the indoor unit PCB board which is controlling the unit and probably the defrost also. Then it's probably the indoor unit PCB board which is faulty?

If that is RAV-SP1400AT-E, than it is outdoor unit SUB PC BOARD (MCC1938)!
Also, order TE sensor.

[SteinarN]

If that is RAV-SP1400AT-E, than it is outdoor unit SUB PC BOARD (MCC1938)!
Also, order TE sensor.

You are informed nearly better than me.

You are correct about the model.

Have to give you a chance and order the PCB and TE sensor.