Compressor of FF – Is it better to replace? [w/ sound files]

[geck0uk]

It’s a single compressor, 140W fridge-freezer (120W compressor). At the moment I know the most about it’s condition therefore to put my basic knowledge to a test, I state the followings:
– I don’t think the age of the appliance is relevant (offset bias). It’s beyond the warranty period, that’s why I need to ask/consider to have it replaced.
– Also type, manufacturer can be ignored. I’ve checked the Internet for product specific issues with no results.

Please let me know if my principles are wrong by asking for any details of the above.

The compressor: [INDENT]Displacement 9.60 cm3
Oil quantity 165 cm3
Maximum refrigerant charge 150 g
Free gas volume in compressor 1600 cm3[/INDENT]

History: [INDENT]The fridge was disconnected/left empty for over a year. After switching back on shortly the compressor failed to start due to relay issues in the control PCB (including sparks). Investigating that issue turned out the running capacitor is dead but the PTC is OK.
With the new running capacitor the fridge is working OK with a temporary thermostat (also with a temporary solution to switch between the fridge-freezer evaporator circuits).[/INDENT]

However fixing/replacing the control PCB can cost up to 1/2 of the price of a new fridge-freezer.

I’m worried about the noise the compressor makes at it’s “warming up” phase. To make it easier for you I created a wave form: [IMG2=JSON]{“alt”:”start-up, running and cut-off”,”data-align”:”center”,”data-size”:”full”,”height”:”317″,”title”:”Fridge-Freezer compressor noise”,”width”:”1082″,”src”:”https://dl.dropbox.com/s/9d8f3jil8n5mlt5/FridgeCompressorNoise.png?dl=1″}[/IMG2]

The sound files (must be downloaded to play): Dropbox link

I prefer to have testable hypotheses: a way (test) to prove the possible explanation wrong. Obviously only if that’s possible.

In return please let me know how can I payback your favour.

I really appreciate any responses.

[geck0uk]

The fridge/compressor has been running OK for the past one month.
A SmartMeter has been installed to the flat recently which allowed me to monitor/measure the load characteristics. (The display updates every 10 seconds).
The result (image has a link to a full sized version via Dropbox):

[IMG2=JSON]{“data-align”:”center”,”data-linktype”:”1″,”data-linkurl”:”https://www.dropbox.com/s/0601rxwh1x40gr8/Fridge-Compressor_Starting_graph.png?raw=1″,”data-size”:”full”,”height”:”288″,”title”:”Fridge-Compressor_Starting_graph.png”,”width”:”598″,”src”:”https://www.dropbox.com/s/0601rxwh1x40gr8/Fridge-Compressor_Starting_graph.png?raw=1″}[/IMG2]

The way I created the chart: I video-recorded the SmartMeter with all other electronic devices off. For all kitchen appliances there’s a fused switchboard, close to the fridge. The switching sound is swift and also loud enough to be audible on the recording. I tried to time the switch-on moments to spread the measurement points within the 10 seconds period (with not a great success).
(I could have measured the voltage on the PTC with a multimeter, however to do so the fridge needed to be “dismounted” from the cabinet; Having all electronic devices off also allowed me to check the main fuse-box of the flat along with checking the power consumptions of each electrical appliance.)
The video files are available under the same link as the sound recordings (#1st post): Dropbox link

For me the main news was that the time for the PTC to “disconnect” the start-winding of the compressor takes up to 50..60 seconds.

Furthermore I’ve learned:

• with the in-rush current of a starting, 120W compressor the usage can result in a peak ~930W (3.875 A) and it can last up to 3+ seconds
• in case the PTC is off (e.g. remained hot after a quick switching back on event) the power consumption of the blocked compressor is ~795W
  The time for the PTC to cool off, in my case, took about 3..4 minutes. From it I conclude that the compressor must withstand the heating power of about 800 watts for at least this period of time (the heating motor lengthens the time for the PTC to cool down) without any serious damage.

I hope it’ll be helpful for others.

[Author]

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