"Art Vanderlay"  wrote in message 
news:j5p2m8$dmo$1_at_dont-email.me...
> On 25/09/2011 3:45 PM, Dennis wrote:
>> I picked up a small fridge compressor with the idea of playing around 
>> using
>> it for a SMD vacuum parts pick up tool, but it behaves strangely.
>>
>> On initial power up it runs fine, very quietly. It quickly/easily pulls 
>> down
>> to 20kpa (-80kPa).
>>
>> However if I disconnect the power and reconnect there is a quiet hum but 
>> the
>> motor is stalled. If I disconnect again then wait a minute or two before
>> reconnecting it powers on fine and will run fine - I've let it run for 5
>> minutes continuously with no problems.
>>
>> As part of the terminals to the motor there appears to be a thermal 
>> overload
>> switch, it gets warm but not hot (guess ~30 Celius)
>>
>> Heres a link to the data sheet:
>>
>>
>> http://www.transtech-co.jp/electronics/en/Library/compressor7.pdf
>>
>> I vaguely recall something about fridges having protection against rapid
>> cycling of the power for some reason - but that could be rubbish.
>>
>>
>> Any ideas?
>>
>>
>>
>> PS: neat home SMD vac pickup video:
>> http://www.youtube.com/user/mikeselectricstuff#p/u/8/pdGSFc7VjBE
>>
>>
> When used in  a fridge as designed if the power is removed then reapplied 
> quickly, the pressure of the gas will cause the motor to stall. By waiting 
> for a period of time for the pressure to disperse into the pipework, the 
> compressor will restart. this usually takes a few minutes.
>
> The thermal overload device on the input terminals will sense when the 
> motor is stalled and results in the compressor cycling on for a short time 
> (about 20-30 seconds), then goes off for about 3-5 minutes. Eventually the 
> compressor will overcome the gas pressure and restart normally.

Thanks for the reply Art. Yep, I found a PTC thermistor under a cover on the 
compressor. Google led me to more infor on how it works.

Now to play with making my SMD pickup.....

Thanks.