That isn't near high enough for R410A, and is much too high for R12.Quote:
Originally Posted by Peter_1
You may not be doing things the wrong way, but you are doing things the hard way.
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That isn't near high enough for R410A, and is much too high for R12.Quote:
Originally Posted by Peter_1
You may not be doing things the wrong way, but you are doing things the hard way.
What if the LP control is being used to control the temperature in a cooler or a freezer?Quote:
Originally Posted by Peter_1
Why is this a difficult concept? I know that the HP control should trip at about 135-140F/57-60C saturated condensing temperature. A glance at my pressure/temperature chart tells me what the pressure setting should be for every refrigerant. Is it somehow easier to remember what the pressure setting should be for each and every refrigerant?
Hi Peter. My oh my what a path this discussion has taken. :)
What is maximum allowable pressure? If the equipment has a pressure relief valve, then I would say that is the maximum allowable pressure, and I would be sure to set the control safely below it's setting.Quote:
I set pressure switches to the max allowable pressure the manufacturer gives me, mostly 26 bar for the HP versus LP just above atmospheric pressure (not for a scroll of course) What is wrong with that? It never gave me problems and no one could ever convince me that this is wrong.
Pressure safety controls, of course, are unrelated to saturation properties. Perhaps the dilemma that has helped this discussion to turn into so much fun is that we are thinking that the high pressure control (simply a safety device) and the low pressure control (not so simply a safety device) are completely different animals even when using the same bellows and switches.Quote:
A high pressure switch is a safety device to protect the compressor going above the max allowable design pressure, given by the manufacturer. So I only do what they recommend me without translating it to temperatures which i find is real b..s.
I have long held the same opinion, although I have no idea why you are separating scrolls from the mix. Copeland CSS classes teach that this is not a good idea to arbitrarily pump down to just above atmosphere. I remember more that the reasons made sense to me than I do the reasons.Quote:
LP just above atmospheric pressure (not for a scroll of course) What is wrong with that? It never gave me problems and no one could ever convince me that this is wrong.
Oil foaming on medium temperature applications during the pumpdown event, when it is unnecessary, perhaps?
The location of the solenoid valve becomes relevant. If you are pumping down a refrigerator with a liquid line solenoid valve located on the compressor unit that is 200 feet away from the refrigerator, the deeper the low pressure control setting, the more frequent the additional short cycles will insert themselves, and temperature control and medium temperature defrosts could become a problem.
A last point, even with low temp stuff, why not take advantage of every psig that a Deg F can provide? R22 low temp ice cream applications force you to hover with a cut out very close to atmospheric temperatures. Other refrigerants permit you to raise the cut out well above atmospheric pressures. Why not take advantage of that? Pressure controls will drift over time, why play it so close to the edge when it is unnecessary?
Fun thread, gents!
In most cases, it would take a fire to reach the relief valve setting. Setting the HP just below the relief valve setting could allow prolonged running at very high pressures, at least causing unnecessary wear and tear, poor performance, and high energy costs, and at worst damaging the compressor.Quote:
Originally Posted by Dan
Does setting it too high cause problems? No, it just ensures that it will never trip. It might as well not be there. It is useless.
I know, compressors for R410A can be set much higher because the manufacturer releases them for a higher pressure.Mitsubishi states testing 5 minutes on 41 bar (4.15 MPa)!!Quote:
Originally Posted by Gary
My statement was for the 'old gasses'.
So.....What do you mean with this? It still works, at least with the machines I installed the last 20 years.Quote:
Originally Posted by Gary
I was thinking more on all those who try to work with a pump-down with scrolls, especially on freezers. Almost impossible and not allowed by the manufacturer due to the pressure differential which will be too high while pumping down.Quote:
Originally Posted by Dan
You seem to be assuming that all LP controls are used for pumpdown systems. I have encountered a great many coolers and freezers which have no temperature control, no solenoid valve, and no pumpdown. The temperature in the cooler or freezer is controlled by cycling the LP control. This is what I was referring to.Quote:
Originally Posted by Peter_1
It always amazes me that people will insist on doing things the hard way, even becoming defensive about it, for no other reason than it is the traditional way to do it. I find it even more amazing that the schools continue to teach the hard way, for the same reason.
People who look at their gauges, then convert those pressures to temperatures, have a huge troubleshooting advantage over those who only see the pressures.
They know what saturated temperatures are typical/acceptable/unacceptable for a given set of conditions. They need only glance at a pressure/temperature chart to know what typical/acceptable/unacceptable pressures are for any refrigerant under current conditions.
Those who think in terms of pressures are lost when they encounter a refrigerant they are not familiar with. They have no idea what pressures are typical/acceptable/unacceptable for current conditions.
Saturated temperature version of the same list:Quote:
Originally Posted by rdocwra
Gas Type, HP, LP@32F/0C Coil, LP@14F/-10C Coil, LP@-22F/-30C Coil
R-whatever, 99F/38C, 32F/0C, 14F/-10C, -22F/-30C
1.you take the max avarage ambient for the region,say 35 deg.
2.take condensor td,say 15k.
3.add 5psi for safety
add 1,2 and 3 =35+15+5=55 degrees. this temp should match the pressure on hp gauge.
That applies to all gasses