Toshiba RAS-10SKVP2-E Temperature issues

[Perry]

Hi all,

Looking for some advice on an issue that has been driving me mad.

So my Toshiba A/C unit runs fine, apart from the fact that the temperature is way off.
It seems to be 4 degrees C out, so for example I set the AC to 20C it will cool down to 16C, if I set to 24C it will cool down to 20C.

It isn't a major issue as I can work around it by setting the temp 4 degress higher or lower than what I want, but I am looking to fix this.

I have already tried replacing all 3 sensors (TA, TC, TCJ) but this makes no difference, I have even tried moving the TA Room temp sensor away from the A/C to another part of the room to see if this helps but the issue remains exactly the same.

I was looking at replacing the PCB next, but only if this would fix the issue.

Can anyone advise if this would be the likely problem part or should I be looking elsewhere on the unit?

Thanks to anyone that can help :)

[Brian_UK]

Just had read the service manual I can't see anything standing out as the likely cause.

Are you measuring the room temperature at the TA sensor location?

Have you tried relocating the TA into a better return air location in the unit?

Two possible fixes...

1. Establish the temperature at TA position, compare it with set point and install a fixed resistor in the TA wire to provide an offset.

2. (My preference) Install a variable resistor and adjust to suit your settings.

[Perry]

Hi Brian thanks for the reply.

To answer your question, yes I am measuring the temperature at the TA sensor location as I did have a digital thermostat located right next to the location that I run the TA sensor to.
That being said, even with the TA sensor located in its correct position (right side of unit, under the case in its holder) and the digital thermostat located on the other side of the room the temperature difference was the same.

I will try locating the TA sensor in front or towards the top of the unit so it is getting more air flow and see how that goes.

I also think that your recommendation of a variable resistor is a great idea, didn't think of that.
I have just had a quick look on Amazon for variable resistors and can only seem to find them with 3 terminals, would I not need a resistor with just 2 terminals as I assume I would cut one of the two wires leading to the TA sensor and wire in the resistor?
Also I assume I would need to ensure it is a 10K resistor as this would then match the TA sensor?

Here is the variable resistor I am looking at: http://www.amazon.co.uk/Aussel-Linear-Potentiometer-Terminal-B10K-5PCS/dp/B0734K6WYP

Thanks again for your help!

[Brian_UK]

That Amazon resistor should be okay, just connect to the centre tap and one of the outers. One will increase as the other decreases.

Don't know whether you have a resistance chart for the sensor but the following figures are from the manual I saw...

⁰C Ohms
10. 20.7
20. 12.6
25. 10.0
30. 07.9
40. 04.5

[Perry]

Just researched wiring one of these in and it seems to be simple enough, I have ordered some for tomorrow, so will fit and see if it works.

Thank you.

[NH3LVR]

Is the resistance of the sensor from 4.5 to 20.7 Ohms or 4.5K to 20.7K?.
This is a little out of my area.

[Perry]

This is from the manual:
Room temp. sensor (TA-sensor) 10kΩ at 25°C

Also this graph:
15629

Got to admit this is my first time dealing with resistances of a sensor.

[Perry]

It works!!
Thanks for the advice Brian, the variable resistor has done the trick. Just hope it continues to work in winter when I use the heat pump mode too :)

[Brian_UK]

Good stuff, glad it worked and thanks for giving the update.

[NH3LVR]

I did something similar once.
The Quality Control People insisted that I install an temperature alarm in a cooler. If memory serves I used a Penn A421.
The issue was that the crew would leave the dock doors open, or fill the room with hot watermelon. When it went on defrost the temperature would rise above 40F.
A strategically locate resistor in a Penn A421 solved the problem.
Only two people knew about it.