Fridge compressor works fine for a few hours than tries to start but fails.

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sula1

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Dear community,

Our air cooled fridge compressor works fine for 12 to 15 hours then tries to start clicking in for 3 seconds then rests for a minute or two then tries again with same result. If we turned it off for the night or anyway a few hours, it will work again for 12 to 15 hours and then repeats the performance.
We are in Italy, so quite hot at the moment, but same area last year and it worked fine the whole summer.

Any ideas? Thanks in advance
 
Definitely start with checking the voltage at the compressor and check ALL connections on both positive and negative sides.
What unit do you have? Are there any diagnostic LED flashes?
 
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as all so far have pointed out, low volts.
Could be one cell going in the domestic bank.
Different controllers have different signals for low volts - my Indel Isotherm cycles through the 3 red/yellow/green lights.
The point at which it cuts out is 10.5volts - one flat cell in a 12v battery.
 
Thanks to all so far. We know we have no problems with our batteries but we'll check the connections at the compressor's end (btw it's a Danfoss)!
 
Happened to us, we beefed up the size of the cables and significantly shortened the cable run - it used to be from the batteries, to the main switch panel and then all the way to the fridge, now it's just batteries to fridge. Anyway the battery bank can get down to lower voltages without what you describe happening. Previously it would start acting up at 12.7v
 
Just a quick observation which may not be relevant, but fridge compressor motors have to start up with no load as they stall otherwise, the clicking is possibly the overload trip because the motor cannot start. It resets after a short time and tries again. The problem is that the compressor may take a little longer to go to pressure drop internally as it is not air being pumped but a liquid through a small orifice if I am right. If the fridge tries to start up too early after the thermostat shut down for whatever reason & the compressor is still pressurised it will fail & the cut out protects the motor from overheating from stalling.
Similar to domestic fridges/freezers. Sometimes they will not turn back on immediately after shut down if it has not rested and the cut out can be heard clicking until the pressure has dropped.
Just a thought.....
 
RichardS said:
Surely that's virtually a fully charged battery? Unless you've got the engine running how did you ever get above 12.7V?

Richard
Click to expand...

Solar and wind genny are charging pretty much 24/7. The original fridge installation had about 5m of thin cable with 5 joins including the switch, that caused the Waeco real problems. It sounds like an extreme version of what the OP has. The fridge will now happily run at 12.2v batteries - under load, which probably equates to about 12.4 rested.
 
RichardS said:
Surely that's virtually a fully charged battery? Unless you've got the engine running how did you ever get above 12.7V?

Richard
Click to expand...

A good thought too :encouragement:

I cannot see how it is low battery voltage, or it would not start after being off for a few hours. More likely to be the thermostat trying to switch the fridge back on too soon.

Check internal fridge temp when it switches off/on to check the stat.
 
johnlilley said:
Just a quick observation which may not be relevant, but fridge compressor motors have to start up with no load as they stall otherwise, the clicking is possibly the overload trip because the motor cannot start. It resets after a short time and tries again. The problem is that the compressor may take a little longer to go to pressure drop internally as it is not air being pumped but a liquid through a small orifice if I am right. If the fridge tries to start up too early after the thermostat shut down for whatever reason & the compressor is still pressurised it will fail & the cut out protects the motor from overheating from stalling.
Similar to domestic fridges/freezers. Sometimes they will not turn back on immediately after shut down if it has not rested and the cut out can be heard clicking until the pressure has dropped.
Just a thought.....
Click to expand...

It doesn't sound like a pressure equalising problem to me, when the danfoss compressor starts up to often or too early it stalls then the fan will run for about 60/90 seconds and the compressor will try again by which time the pressure has equalised and the compressor will run then the whole cycle will start again. If the compressor does not run at all and you have checked EVERY connection then the next step is to bypass the thermostat.
 
Also, if I remember correctly, a digital multimeter is not very effective for measuring the voltage drop at the point the compressor tries to start, I believe the voltage drop happens too quickly for the meter to be an accurate/definitive diagnosis.
I would recommend making new temporary connections to the terminals on the control unit using thick wire and a fully charged battery. If the problem still exists you can rule out your electrical connections. Then bypass the thermostat, if that fails to get compressor running then see if you can get hold of a repacement controller, borrow one if possible or send your one off to be checked.
 
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Apologies Sula, having re-read your original post, my advice is probably not relevant. The fact it runs properly for a while would suggest some other issue. Maybe some kind of intermittent blockage? You could try gently tapping the pipe work with a screwdriver handle. I'm sure somebody with more knowledge than me will be along with some better advice.

Kieran
 
Could it just be the unit overheating and the thermal protection kicking in? I had a problem just as described by OP. The compressor unit fan did not run up to full speed. Replaced the fan and all is well.
 
Thanks everybody. Typically, since weiting the post, the fridge has behaved and therefore have not been able to test some of the suggestions given. The connections to the compressor may be the more likely culprit, but at a first inspection, they looked fine. The only thing I've done since writing the thread is increasing the temperature of the thermostat. I'll try to lower it again and see if it misbehave again. Thanks again for your help so far anyway!
 
sula1 said:
Thanks everybody. Typically, since weiting the post, the fridge has behaved and therefore have not been able to test some of the suggestions given. The connections to the compressor may be the more likely culprit, but at a first inspection, they looked fine. The only thing I've done since writing the thread is increasing the temperature of the thermostat. I'll try to lower it again and see if it misbehave again. Thanks again for your help so far anyway!
Click to expand...

Don't rely on "looks" for connections. A mate was aboard for the first time after launch this season and I got a panic call because his voltmeter showed the domestic plummeting to 5V after a few seconds. He turned all batts off, and I went aboard with clamp meter, expecting to see a huge discharge current, with the subsequent task of finding a short... There was no discharge current... A quick pole to pole voltage reading showed 12.8... The clamp on post connectors looked fine, but on dismantliing the "extras" that had been added, there were lots of bits of corrosion , which when sand papered off resolved the issue. Grease over the top then followed....
 
Danfoss BD35 compressors have a built in diagnostic feature. If the one you have is an old model, it's easy to fit a small led between the small + and D terminals. The number of led flashes at shut down will tell you where the fault is.
 
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