Suction line pressure drop

[RBM]

Hello, I have a system that doesn't feed evaporator properly, frosts first part of evaporator only - the system has a pressure drop of about 15 psi in suction line and I wonder if that would cause the evaporator to be starved of liquid? The superheat is about 10 k when measured at evaporator but this doesn't seem right as the coil is iceing only at the start of coil. Gas charge ok - full sight glass.
Besides loosing capacity what symptoms would suction line press. drop cause?
Any advice much appreciated

[Magoo]

Partial frosting of evaporator and a full sight glass would tend indicate an expansion valve problem, not feeding enough liquid to feed all circuits if fitted with a distributor. Similar if no distributor fitted.

[RBM]

Partial frosting of evaporator and a full sight glass would tend indicate an expansion valve problem, not feeding enough liquid to feed all circuits if fitted with a distributor. Similar if no distributor fitted.

Thanks for your reply, will check out TX valve again. Suction line press drop is too much do you think this will cause any problem beyond reduced system capacity?

[Tesla]

Hi RBM
I have to go with Magoo answer and ask why you would be asking about suction line pressure drop or is it really low suction pressure? as there is a difference. Are there any components in suction line like suction filter? What is your method of measurement and exactly where are the measurements taken?. I was taught to expect around 2 or 3 PSI pressure drop in the suction line so 15 sounds pretty big. Too much suction pressure drop would effect capacity and oil return. Causes could be may like undersized line but only guessing with out more info. Give us what you can on the system measurements please.

[Sandro Baptista]

Thanks for your reply, will check out TX valve again. Suction line press drop is too much do you think this will cause any problem beyond reduced system capacity?

The head loss on the suction pressure would increase the evaporator pressure, so higher evaporating temperature will reduce the capacity...but it is not responsible by the partial frost caused by the lack of feeding. In fact as the evaporator exchanges less heat the expansion valve would have less lack of capacity. Try to close a little the suction valve (increasing the suction loss) of the evaporator and will see the frost will disappear.

Where do you have the sight glass? What counts is the liquid state at the inlet of the expansion valve...Maybe on the path the HP liquid to the expansion valve the head loss by the solenoid valve, valves, curves, pipe, rise of the liquid the the liquid could flash turning part of it to vapor and so reducing the expansion valve capacity. Liquid subcooled may knock out that issue.

[RBM]

Thanks again for replys, I know I have incorrect pipe size of suction line causing press.drop but it looks like there is another issue as well ie TX valve, orifice which I will need to look into.

[Sandro Baptista]

Thanks again for replys, I know I have incorrect pipe size of suction line causing press.drop but it looks like there is another issue as well ie TX valve, orifice which I will need to look into.

See if the liquid feeding line is not to small (low internal diameter), small electric valve, etc...The best way is to put a sight glass at expansion valve inlet. If bubbles occurs the expansion valve will lose capacity.

[Royal241]

clogged filter at txv

[Royal241]

[QUOTE=Royal241;277111]clogged filter at txv[/QUOTE
filter screen