I have a few beore I leave so heres my parting thoughts on your
defrost problem. I use a 6F differential on the control setting. So
with a 35F box cut out air temp would be 32F and cut in temp would be
38F. So at a target avg of 35.. yeah, you might want a defrost
I'd bump the temp up a half a degree or so to keep the air temps above
32F. That way you maintain a more consistant box temp which is good
for the product and the consumer.
Since I'm not the worlds leading expert on refrigeration/HVAC,
I can only comment on my own personal experience with the various
equipment over the last four decades. I would have to research
the subject to give you any sort of proper and precise explanation.
All I can say is that every R22 walk-in cooler I've ever seen, has
had a defrost system except for the homemade ones that didn't work
until they were equipped with some sort of defrost system. Every
factory built condensing unit for an R22 walk-in cooler including
walk-in freezers has had some sort of defrost system. Passive for
the coolers, active for the freezers. I'm always willing to learn
new things so if you can tell me more and point me to the source,
I have no problem being corrected. When it comes to education, my
ego doesn't get in the way.
On Wed, 29 Jul 2009 14:53:24 -0500, The Daring Dufas
What do you mean when you say "passive for the coolers"?
I agree every ref system needs some sort of defrost. it could be
either electric, hot gas, manual, or off cycle.
What you said was every r22 cooler needs a defrost clock. I don't see
why it would. Most refers are designed to have a 2/3 run time. The
other 1/3 is off. When it is off the space warms and any light
accumulation of frost should melt off before the next start. About
the only time I have seen or had to put a timer in is when the
customer wants the coldest beer in town and wants the coolers to run
30-35F. At those temps there is not enough off time above freezing F
to allow for a natural defrost and a defrost clock is needed.
Why is it an r 22 cooler needs a clock when a r 12 cooler didn't.
The evap temps are the same for each and every ref used for medium
temp work at a 10 delta. The refrigerants pressure/temp relationships
change with the type of refrigerant and they all have different
boiling points and properties. Some temps are cooler at x pressure
and some are warmer. They each have a different capacity per pound
circulated and all that jazz but those factors are why there are
different ratings for compressor duty and the type of refrigerant used
I hate to type and run but I have to pack the bike now and off to
On Wed, 29 Jul 2009 21:21:18 -0400, .p.jm.@see_my_sig_for_address.com
Its not as bad as it looks on TV. :)
I got back last night around midnight after leaving the Sioux Falls
area at 5:30am. Ran in over eight hundred miles of pouring down rain
and a cross wind that was unbelievable. All in all it was a good
trip and we logged over 3200 miles.
Careful out there, the cage drivers are out to get you.
Passive defrost: Cut the flow of refrigerant, leave the
evaporator fan/fans running. Ambient temp rises melting
the frost buildup. Active defrost: Cut the flow of freon,
turn off the evaporator fan/fans, turn on electric heaters
or use a hot gas defrost cycle to melt the ice buildup.
I've never had the R12 systems freeze up unless the temp
was set too low or the evaporator air flow was impeded.
R22 walk-in coolers always seem to freeze up without a
timed defrost cycle. All those years ago when I was at
college studying for my degree in rocket surgery, the
classes never covered walk-in coolers so I can't give you
a scientific explanation.
Wasn't sure what you meant by rotary so I looked it up. According
to my research it's a screw pump. If that's the case then I have
changed oil in a rotary compressors before.
Create pressure in the system then valve off any means for the
pressure to bleed off once you shut it down. Find the appropriate
outlet for the used oil and let the trapped are force it out.
Alternatively provide an outside source of air pressure and do
On 27 Juli, 20:42, firstname.lastname@example.org wrote:
Thanks, yes, the big rotarys are of screw type but this is a small
hermetic rotary compressor (as used in many residential split AC's),
no service valves etc for oil; the oil is never ment to be changed.
All ideas are welcome!
On Mon, 27 Jul 2009 18:19:19 -0400, "Old and Grunpy"
They are not veins. They are screws that are machined in a way that
compresses the gas or liquid in a given direction.
Sorry. You are wrong. Vein pumps are Vane pumps. Vane pumps can be
considered a rotary compressor, but when talking about air conditioner
compressors the term" rotary compressor" is most likely a rotary screw
Hydraulic pumps can be any type of positive displacement pump. Usually
a high pressure pump such as a piston, vane, gear or even a screw
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