metering device restriction

[TheWolfLA]

Hey guys.
main point: if a metering device is restriced does the high side pressure drop? why?

i have read that if the metering device is restriced the high and low side pressures will fall. I under stand that a restriced metering device would cause the system to do the same thing as pump down, (right?), and pump all refrigerant into the high side, stopping at the restriction in the metering device.

my question is, if all the refrigerant is in the high side, why would the high side pressure drop?
my guess: since all the refrigerant building up in the line before the restriceted metering device would be condensed. my guess is that this refrigerant stopping at the metering device is being condensed into 100% liquid and that is why there is a pressure drop on the high side. (pressure gauges only read saturated pressure) ,and since it would be completly or mostly pure liquid, (there would be less saturation) the saturation pressure (h/s gauge pressure) would drop.

i think i have read that during pump down both high and low sides go down to 0 psig. is this correct?
when a system is pumped down does head pressure drop?
is this the same as the high side pressure drop in a restricted metering device?
:payattention:

[james122964]

there are threads on this, and I am not trying to be mean, but, if you read them you will find why I recommend against starting another.

Jim

[keviekev70]

Understand superheat and subcooling it will clarify most of your questions.

[hvacpope]

Hey guys.
main point: if a metering device is restriced does the high side pressure drop? why?

i have read that if the metering device is restriced the high and low side pressures will fall. I under stand that a restriced metering device would cause the system to do the same thing as pump down, (right?), and pump all refrigerant into the high side, stopping at the restriction in the metering device.

my question is, if all the refrigerant is in the high side, why would the high side pressure drop?
my guess: since all the refrigerant building up in the line before the restriceted metering device would be condensed. my guess is that this refrigerant stopping at the metering device is being condensed into 100% liquid and that is why there is a pressure drop on the high side. (pressure gauges only read saturated pressure) ,and since it would be completly or mostly pure liquid, (there would be less saturation) the saturation pressure (h/s gauge pressure) would drop.

i think i have read that during pump down both high and low sides go down to 0 psig. is this correct?
when a system is pumped down does head pressure drop?
is this the same as the high side pressure drop in a restricted metering device?
:payattention:


the refrigeration loop moves btus from one end to another, if the refrigerant stops moving due to a restriction so does the btus and with no or very little heat making it to the condenser the amount heat being rejected drops along with the head pressure.

[hvac wiz 79]

Hey guys.
main point: if a metering device is restriced does the high side pressure drop? why?

i have read that if the metering device is restriced the high and low side pressures will fall. I under stand that a restriced metering device would cause the system to do the same thing as pump down, (right?), and pump all refrigerant into the high side, stopping at the restriction in the metering device.

my question is, if all the refrigerant is in the high side, why would the high side pressure drop?
my guess: since all the refrigerant building up in the line before the restriceted metering device would be condensed. my guess is that this refrigerant stopping at the metering device is being condensed into 100% liquid and that is why there is a pressure drop on the high side. (pressure gauges only read saturated pressure) ,and since it would be completly or mostly pure liquid, (there would be less saturation) the saturation pressure (h/s gauge pressure) would drop.

i think i have read that during pump down both high and low sides go down to 0 psig. is this correct?
when a system is pumped down does head pressure drop?
is this the same as the high side pressure drop in a restricted metering device?
:payattention:



no the high side will drop slightly .. unless grossly overcharged then it will rise

[Andy Schoen]

Hey guys.
main point: if a metering device is restriced does the high side pressure drop? why?

i have read that if the metering device is restriced the high and low side pressures will fall. I under stand that a restriced metering device would cause the system to do the same thing as pump down, (right?), and pump all refrigerant into the high side, stopping at the restriction in the metering device.

my question is, if all the refrigerant is in the high side, why would the high side pressure drop?


As low side pressure drops, refrigerant mass flow thru the compressor drops. As refrigerant flow drops thru the condenser, so does pressure due to reduced TD.

[Phase Loss]

i think i have read that during pump down both high and low sides go down to 0 psig. is this correct?

You will read 0 psig on the high side while the system is pumped down.

ONLY

if you are put your gauge downstream of the liquid line solenoid or king valve (if you closed the king valve)

If you have your gauge upstream of the liquid line solenoid, you will see your discharge pressure drop as your heat transfer stops...unless your grossly overcharged or your receiver/condenser do not have the capacity to hold the normal system charge. Then your pressure will raise, due to trying to stuff 10# of stuff into a 5# bag.

[TheWolfLA]

and so I've learned:
In a normal cycle the refrigerant in the evaporator is about 50% saturated substance (between liquid to vapor change). the saturated state allows the refrigerant to absorb many BTU's. these BTU's are also given off in saturation, in the state change from a gas to a liquid in the condenser.
during pumpdown the evap goes down to zero? (what abouty systems that operate below zero? , or pressure just goes down?) so the saturation level in the evap goes down alot, and less BTU's are absorbed. this means less BTU's are transferred to the candenser, and thats why the condenser temp/press goes down. the condenser will also be very unsaturated.
why would condenser pressure rise if over charged, you are just shoving too much refrigerant into a confined space, raising the pressure, vs a normal pumpdown is designed to hold all refrigerant.
thanks guys.

[hvacpope]

and so I've learned:
why would condenser pressure rise if over charged, you are just shoving too much refrigerant into a confined space, raising the pressure, vs a normal pumpdown is designed to hold all refrigerant.
thanks guys.

its like 10 pounds of crap in a five pounds bag:p