# Freezer Hiss



## salman (Mar 13, 2005)

I just noticed something unusual, or at least unusual for me. After coming back from a three day trip and unloading the fridge/freezer, I noticed that the freezer would hiss right after I closed it for about 5 seconds. I then try to open the freezer door and it seems to be tight, like a vacuum was just pulled inside the freezer compartment.

I tried this sequence several times and it seemed to repeat itself. I tried it with the unit on and off. I also tried it with the outside gas turned on and off. Note the unit was still pretty cold at this point, close to freezing so I haven't tested after letting it air out for a few days.

The engineer in me is still trying to understand why it would pull a vacuum upon closing. I guess if you bring in warm air from the outside and close the door, the unit will quickly cool the warm air. By cooling this will drop the pressure inside, and if anything, air would be pulled in to equalize the pressure. I'm rambling here.

Any thoughts are appreciated.

Sal


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## PDX_Doug (Nov 16, 2004)

Sal,

I have noticed the same thing in ours. My assumption has been that there is actually a pump in there creating a vacuum seal of the door. Could it be to counter the movements and vibration of the unit while the coach is in motion?

Just a guess.

Happy Trails,
Doug


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## salman (Mar 13, 2005)

Doug, it may very well be normal. That was my thought too. I'd never heard it before, but I might have just missed it.

Sal


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## camping479 (Aug 27, 2003)

> The engineer in me is still trying to understand why it would pull a vacuum upon closing. I guess if you bring in warm air from the outside and close the door, the unit will quickly cool the warm air. By cooling this will drop the pressure inside, and if anything, air would be pulled in to equalize the pressure. I'm rambling here.


Makes sense to me.



> I have noticed the same thing in ours. My assumption has been that there is actually a pump in there creating a vacuum seal of the door. Could it be to counter the movements and vibration of the unit while the coach is in motion?


No pumps, just basic physics I think.









Mike


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## MaeJae (May 12, 2005)

Ours hissssssses too.

Camp-on sunny
MaeJae


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## California Jim (Dec 11, 2003)

Mine does the same thing. The differing temperature theory sounds well.....sound! I don't believe I have heard the unit do this in the winter when it's cold so it makes sense.


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## Ghosty (Jan 17, 2005)

I thought it was becuase there is a small vacuum pump that creates under-pressurization in order to keep the door from simply not closing properly...

but my private school educated engineer wife tells me that it has to do with temperature inversions -- cold vs hot -- an ideal refrigeration cycle between Th and Tx designed to remove heat from a thermo-load by using its latent heat where a minimal specific work (J/kg) is described thus causing suction -- etc etc ...

OH CRAP !!! SHES GETTING HER TEXTBOOKS OUT....

aaagghhhhhhhhhhh!!!!

RUN AWAY RUN AWAY


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## CamperAndy (Aug 26, 2004)

Contributing to the sound, the seals are sprung internally and expand when the door is open. When you close it the seals compress and push air out the corners.


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