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Old 07-08-2013, 02:42 PM   #1
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Power crankcase heater for 24 hours before starting new HP?


If an installation manual for a split heat pump says to turn on the 240v for 24 hours before system start-up, is this really necessary in 60-90 degree summer weather?

Is the purpose to get the compressor warm (which July weather does w/o a crankcase heater), or to get it warmer than the rest of the system to make sure there's no liquid in the compressor?

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Old 07-08-2013, 04:16 PM   #2
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Power crankcase heater for 24 hours before starting new HP?


I can see the posts now....."My contractor installed a new system today and he said he won't start it up until tomorrow!!! Should I tell him I want my money back?"


Not necessary.

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Old 07-08-2013, 05:56 PM   #3
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Power crankcase heater for 24 hours before starting new HP?


it is only needed if it goes below 50F overnight. after that the ambient temp will vaporize any liquid refrig in the compressor so no harm is done.
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Old 07-08-2013, 06:03 PM   #4
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Power crankcase heater for 24 hours before starting new HP?


It's unfortunate when the book includes stuff that nobody does and doesn't need doing (like this).

Then when it comes to things in the book that nobody does but need doing, it's harder for guys like me to point at the book and say "It says here you're supposed to flow nitrogen before you light that torch".
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Old 07-08-2013, 06:12 PM   #5
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Power crankcase heater for 24 hours before starting new HP?


If the manufacturer suggests it to save possible contamination of the oil why would you not want to turn it on as the installation manual says. This makes about as much sense as only putting 3-1/2 quarts in a 5 quart engine to save money because the oil pressure seems to be the same.
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Old 07-08-2013, 07:02 PM   #6
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Power crankcase heater for 24 hours before starting new HP?


Quote:
Originally Posted by taxmantoo View Post
It's unfortunate when the book includes stuff that nobody does and doesn't need doing (like this).

Then when it comes to things in the book that nobody does but need doing, it's harder for guys like me to point at the book and say "It says here you're supposed to flow nitrogen before you light that torch".
The book is great. Its the instruction manual for a great install and there are important steps like N2 and proper vacuum.........what if every online review had to include those 2 steps........
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Old 07-08-2013, 07:21 PM   #7
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Power crankcase heater for 24 hours before starting new HP?


Fairview - Possible contamination of the oil?

Is that in reference to oxygen free brazing or preheating the compressor?
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Old 07-08-2013, 08:44 PM   #8
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Power crankcase heater for 24 hours before starting new HP?


Quote:
Originally Posted by taxmantoo View Post
Fairview - Possible contamination of the oil?

Is that in reference to oxygen free brazing or preheating the compressor?
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Google A/C heater and Wikepeeeedia can X-plain it better than I can. I kant evun spel it.
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Old 07-08-2013, 09:14 PM   #9
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Power crankcase heater for 24 hours before starting new HP?


I see. When the coil gets warmer than the compressor, refrigerant boils in the coil and condenses in the compressor. Depending on how much temperature change it has undergone since it was built, there might be a lot of 410a that condensed in the in the crankcase diluting the oil. Therefore you've got to make sure it has boiled out before you start the system up. I've got to believe that if 90% don't N2 purge during brazing, 99% don't run the crankcase heater overnight.

I had that totally wrong. I thought it was the same as an automobile crankcase heater which thins the oil so it flows better.

Quote:
From Wiki:
A crankcase heater's sole purpose is to prevent refrigerant migration and mixing with crankcase oil when the unit is off, and to prevent condensation of refrigerant in the crankcase of a compressor. The crankcase heater keeps refrigerant at a temperature higher than the coldest part of the system.

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