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Old 02-28-2021, 10:40 PM   #21
redwire
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

These timer motors run constantly I thought?
The switch seems to be in series with the compressor, so they disable it, run a heater cycle to defrost, and then allow power for the compressor again.

You could check the timer motor's resistance (pin 1-3) to see if it is open-circuit or not. The leads are not soldered to the tabs so maybe a bad connection. Some diagrams show a resistor or fuse "C"? in series with the timer motor.

Sankyo/Hitachi TMDFX05CD1 is a special cycle time, 6min/12hr.
TMDF706CD1 is close, 7 minutes defrost with 8hr cycle (50Hz).
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File Type: png sankyo timers001.png (45.8 KB, 4 views)
File Type: png tmdf002.png (248.0 KB, 7 views)
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Old 03-01-2021, 11:02 AM   #22
R_J
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

The schematic of this fridge is in post#11, You can see that the thermostat switches the a/c on and off to everything but the fridge lamp. The defrost timer only runs when the thermostat is closed, When it is time to run the defrost cycle the compressor is turned off. The defrost cycle time is not that critical as the amount of frost built up is also not predictable.

Last edited by R_J; 03-01-2021 at 11:06 AM..
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Old 03-02-2021, 01:17 AM   #23
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

Quote:
Originally Posted by R_J View Post
The defrost timer only runs when the fridge/compressor is running. The defrost motor is connected across pins 1 & 3, check the resistance of the motor, if it is good then maybe you can get some type of cleaner to wash out the motor and the reduction gears inside it? If not just replace the timer, If you can find a used one it should be ok, you can order them off the internet, just be sure to get the right voltage (ac200~240)
#54 on the diagram is that a temp sensor for the heating element? I'm getting open reading with the meter. How do I test that? I think it might be faulty as well. There are two thermostats in the freezer compartment one is embedded in the coils and the other one next to the fan motor. How do I check them with a meter?

Last edited by SuperAman; 03-02-2021 at 01:56 AM..
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Old 03-02-2021, 10:48 AM   #24
R_J
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

I don't know which one it is but if you look at the schematic, there are two, a thermal fuse and a defrost thermo (thermostat) , You said that when you turned the defrost timer so it would defrost that it was working and heating up. if this is the case both thermo devices must be working.

Did you check the defrost timer motor resistance? If the defrost element was heating up when you turned the timer to its defrost position, you have likely found the problem, if the other parts were bad it would not heat up.

Last edited by R_J; 03-02-2021 at 11:17 AM..
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Old 03-02-2021, 02:32 PM   #25
redwire
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

If the fridge runs say 6 minutes every hour (10% duty cycle) with a 6min/12hr defrost timer (wired to the compressor) it will defrost every 5 days for 1 hour. Seem too long to me, but not relevant to OP's problem. It might be a schematic error.
I've had problems with a leaking door seal on the freezer causing the evaporator coils to ice up.
Reposting the schematic for the Hitachi fridge.

The fixed thermostat in the evaporator coil goes open-circuit when it's hot, but will read zero ohms cold - Some popular defrost thermostats: Open 45F, Close 25F, Differential 20F; another is Open 55F, Close 35F, Differential 20F. Not zero ohms at room temperature.

So the thermostat needs close to freezing or colder for the switch contacts to close.
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Old 03-02-2021, 06:34 PM   #26
R_J
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

I believe the defrost timer in my fridge works like this, for every 6 hours of "compressor run time" the timer will then defrost for 25min.
The TMDFX05CD1 = for every 12H of run time it defrosts for 6min

Last edited by R_J; 03-02-2021 at 06:54 PM..
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Old 03-02-2021, 11:58 PM   #27
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

Quote:
Originally Posted by R_J View Post
I believe the defrost timer in my fridge works like this, for every 6 hours of "compressor run time" the timer will then defrost for 25min.
The TMDFX05CD1 = for every 12H of run time it defrosts for 6min
So can I replace mine with one that runs 6, 8, or 10 hrs? I don't think I can find one locally that runs 12hrs. Importing one would be cost prohibitive (customs duties and all).
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Old 03-03-2021, 12:01 AM   #28
SuperAman
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

Quote:
Originally Posted by R_J View Post
I don't know which one it is but if you look at the schematic, there are two, a thermal fuse and a defrost thermo (thermostat) , You said that when you turned the defrost timer so it would defrost that it was working and heating up. if this is the case both thermo devices must be working.

Did you check the defrost timer motor resistance? If the defrost element was heating up when you turned the timer to its defrost position, you have likely found the problem, if the other parts were bad it would not heat up.
I will check it, I put it back together, so I'll have to take it apart again. What kind of resistance values should I be getting from the timer motor?
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Old 03-03-2021, 09:28 AM   #29
R_J
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Default Re: Hitachi Refrigerator R-Z270AUN7KV not cold.

I don't know what the timer motor resistance will be, but it is likely fairly high, If it reads anything but open it is likely ok. You can replace it with a different duty cycle, it's not that critical, It doesn't know how much frost is built up at any time so anything will work better than nothing, If you put a lot of hot steamy food in the fridge it will frost up faster.
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