Compressor in freezer sets of RCD after a few seconds

Thread Starter

Pyrdon

Joined Mar 17, 2010
13
Would be glad if someone was willing to help out..

Okay, so I came back after a few days of vacation and found out that the power was off in the apartment. Apparently the Residual Current Device had triggered. A bit of troubleshooting found the freezer to be the culprit (luckily we have the warmest summer in 250 years or something, yummy food). The problem is that whenever the compressor starts, 1-2 seconds later the RCD triggers. Turning it back on and the same thing happens. I have done the following observations/steps to troubleshoot (in somewhat chronological order).
  1. Unplugging the "start box" of the compressor
    The fridge gets power, lights on etc. The compressor does of course not start, and does thus not trigger the RCD
  2. Attempts to measure the three compressor pins ála whats found on internet to determine if there are anything wrong with the windings
    Nothing wrong as far as I could find (have a horribly unreliable multimeter, new one ordered).
  3. Temporarily disconnecting the ground wire
    The compressor starts, but stops after the same time as before. As the ground wire is disconnected, then the RCD of course does not trigger.
  4. Removing what I understand is the overload protection in the start box housing and replacing with a short circuit
    RCD triggers as before
  5. Removing the capacitor (thought it was a start capacitor, but now think it rather is a run capacitor)
    RCD triggers as before (without ground wires just shuts off compressor)
  6. Bought a new capacitor (5uF 400V instead of 4.5uF 400V)
    Still believed that it was the start/run capacitor that was not working. Believe I saw a slight difference, but can honestly not remember the exact details. I believe that sometimes the compressor just shut off (without triggering the RCD) the first time. Coming back again after a few minutes the RCD triggeres.
  7. Opened up the start box to measure the PTC thermistor
    I wanted to see what was inside the start box and found this ceramic disc. Took it out and found out it was a thermistor (A196) to help starting the compressor and then limit the current. Measurements gave resistance of ~15 ohms at RT and up to 25 ohms or something when I heeated it with my soldering iron a bit (unknown temperature). Working? Broken?
  8. Removed the PTC thermistor (open)
    Don't know why I came to this conclusion but wanted to see what happened if I removed the thermistor. The result is that the compressor starts and keeps running without triggering the RCD (all except one time, in which it shut off and then worked the next round the fridge tried starting it). It has now been on for the whole day, the freezer temperature is ~ -19C.
Questions:
  1. Is it a run or a start capacitor? It is in parallel with the PTC which are both connected between the start/run pins on the compressor. I believe it is a run capacitor? Does it affect the start at all? The 1-2 seconds that I talk about, is that "start" or is it already started and thus running?
  2. How do I properly determine if the PTC is broken? Varying between 15-25 ohms in temperatures between 30 - 100 C ok? There are some signs of the surface finish being discolored, but it is intact.
  3. Why does it start properly without the PTC? Why does it trigger the RCD? I have not tested if the old capacitor works without the PTC connected or if it is a combination of new capacitor and removed PTC
  4. Do I need the PTC? For what? Help starting the compressor? Safety? Can I simply ignore it and run without it?
  5. The compressor gets a bit warm on the outside (~60 degrees). Enough to burn fingers, but nothing to worry about I guess?
  6. The fridge is set to -16, but my thermometer measures -20.4 at the top now. Compressor still not turned off. Have I somehow stopped it from turning off? Or does it never turn off?
    EDIT: I however see now that when I unplug it for the night (don't want to take any risks), the temperature drops down to -13 after 10 min. So maybe the air has not circulated well enough and I am measuring the cold air entering the fridge. I will have to try again tomorrow. How long would I have to expect it takes to cool a full-size freezer from around 0 to -20?
  7. A bit unrelated as I think it has nothing to do with my freezer problems: There are some sticky tar-like substance wrapped in a plastic bag or something that I believe was wrapped around the pipes going between the compressor and the condenser. As these pipes become warm, it has molten and was hanging from these pipes. It has now completely fell off and is just a bag of goo. What is this? Leaking something? Some kind of insulation? Cooling? Vibration damping? Can I just throw it (I can take a picture and attach if unclear)?
  8. EDIT 2: Now tried to run it with the old capacitor. As the original setup, but with the PTC removed. Plugged in, but stopped after 2 seconds. Replugged it, and stopped after 2 seconds again. Waited until fridge attempted to start it again. It starts, but after 2 seconds the RCD triggers. Resets the RCD, but now it is completely silent and does not seem to start at all. Only tried once.
Except for the questions above. What's the next step? Is it working now or what can I do?
 
Last edited:

debe

Joined Sep 21, 2010
1,294
I would bet that the compressor has internal leakage from the windings to ground triping the RCD. Check for leakage with a Megger.
 

Dodgydave

Joined Jun 22, 2012
10,321
Remove the earth wire, and plug it in and get a dvm (Voltmeter) and measure the voltage between Earth and Neutral, and Earth and live on the freezer , chances are there will be a small voltage between Earth and Neutral, as it sounds as though the insulation is leaking, probably in the compressor.
 
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