Suction line?

Hi guys a quickie on a/c,

My boss just got me to endo flush an old system because the indoor/outdoor units are being replaced but keeping majority of the pipework to save on instalation time, but now the new unit has arrived the suction line is spec at 5/8" but the exiting pipework already installed is 3/4". The liquid line is the same 3/8".

He says this is o.k as the refrigerant will have less resistance in the suction line thus making it more efficiant.

is this the case? and if so, as the unit has a reversing valve what will happen when the sytem is heating? will the suction line now the hot gas line not be reduced in pressure causing lower temps thus lower heating efficiency.

plz tell me more is my boss being a cowboy or is he correct?

2 scenarios here.

An over sized suction gas line will create less resistance but will also cause lower suction velocities due to the larger cross sectional area, and this may (repeat - may) cause problems with oil return under low load conditions. The best people to ask about this is the new equipment manufacturers.

Second, the heating capacity should not be affected, as the existing hot gas line should already be well insulated and the system should have been charged to take into account the increased volume of this line (in cooling mode) to maintain the balance point.

Depending on the length of pipe, and the increased system gas charge, you should make sure that the suction accumulator is still sufficiently sized for the overall charge.

P.S. We've had problems using Endoflush - getting it all out of the system - and we've lost a few compressors prematurely. Needless to say - we don't use it any more.

Cheers frank thnx for fast reply, i know what u mean about the endoflush i had problems getting it out my self to be honest i cant see the compressor lasting long, but as my boss says this is the "trial unit" rather large unit to "trial" it on as we have a number of working sytems sat at our yard doing nothing but hey, What do i know? :-)

sorry to bounce my own post but just had a thought is there anyway to calculate extra gas required or as in most cases different manufactures require different amounts?

Look the trick is that you still want to achieve as much suction cooling back to the compressor as possible without cuasing high head pressures. I would be charging the system keeping an eye out on head pressures and suction pipe temps.

Your boss is correct. The larger liquid line will have slightly lower pressure loss between the condenser and expansion device, so less subcooling is required to prevent premature flashing.

Considerations of flashing do not arise from the evaporator to the condenser, so there the idea is to minimize compressor work by minimizing pressure loss. So the one size larger suction/hot gas pipes should slightly enhance performance.

There could be a problem with the 30m (100 ft) equivalent length between the condensing unit and evaporator. That is, of course, liquid accumulation in the suction line during shut down. Consult with your rep, and follow the mfr recco, which may include adding a pump-down feature.

Charge by pressures, and the larger pipe volume will not be a factor.

Oil return is generally only a problem when the condensing unit is higher than the evaporator. Then, it is essential to size the suction pipes to return oil up the riser. Charts are available from major mfrs to check maximum riser sizes for various refrigerants.

hey guys, did you see the date????

in short, he's boss is a morron and have still a lot of learning to do about refrigeration.