Weak Compressor, Restriction in the condenser, or something else

[Newsurvey6]

I am new to the forum so please forgive any mistakes. I am working on a Carrier split system heat pump. I repaired a leak on the condensing unit, evacuated and recharged the unit.Now the liquid line is refrigerating as soon as it leaves the condenser, but instead of my suction pressure being low it high 95psi. The liquid line pressure is only 150 psi with the pressure difference being so little it leads my towards weak compressor. The customer tells me that compressor has recently been changed and it does look very new, but we all new is a relative term. I am thinking a weak compressor but I cant get the liquid line refrigerating straight out ofthe condenser off my mind. Any thoughts?

[monkey spanners]

Could it have a blocked drier (or kinked line etc) and have been overcharged to get the suction pressure up?

Think i'd be weighing out the charge and back in again to be sure its correct, a new drier wouldn't hurt if it has one fitted.

If it is a weak compressor then i would expect it to be pulling low amps.

[aramis]

Did you circulate nitrogen when you fixed the leak?

There is a restriction where you sense a temperature difference.

You should check for dirt or something like it.

[Newsurvey6]

Thank you for your comments. I am use to have someone to talk through a tough diagnosis, so this really helps.
I did suspect the drier but when I checked further the refrigeration starts before the drier. It is a larger unit and does not have a weighted factory charge. I charged it with 16 lbs with is close to what the other similar unit on the building are charged with, and I stopped during the charge to check pressures and truthfully at 8lbs it was running 70/ 130. I only continue the charge at the advice of my supervisor. But if over charge was part of my problem shouldn't my liquid line pressure but high also? You are correct about the amps it is rated at 29 but only pulling about 20. I did have some nitrogen pressure on the line when I was soldering.

[aramis]

If you have a valve on the high side downstream from your gage you can thest whether the compressor is weak by slowly closing the valve and checking if the pressure goes up to around 300 psi your compressor is not weak. I suppose you are not using R410a nor CO2.

The most probable cause is a restriction in your condenser, peace of metal, plastic, bumped curve, or something else.

If you have some way to measure the pressure drop through your condenser and it is higher than a few psi, you have a restriction.

If this is a heat pump the expansion device of the other cycle could be stuck.

When you get rid of the restriction you will probably notice the system is low on refrigerant.

[Brian_UK]

What refrigerant is being used, pressures not much use without that info. ;)

[Newsurvey6]

It's R-22. I had a thought if the outside check valve is not working would it cause these symptoms?

[hvacrmedic]

High suction/ low head. Here are the most common causes (in no particular order):

Over-metering-- expansion device not seating, stuck open, or missing.
Under-pumping-- defective compressor
Bypassing-- Reversing valve stuck in mid position or compressor internal bypass active.
Defective gauges/measurment error.
High evaporator load with either low ambient or wet condenser coil.

20 amps on a compressor with an RLA of 25 isn't low. It's actually a normal amperage. The compressor won't pull RLA except under extreme conditions, dirty condenser coil, etc.

The normal amperage rules out an under-pumping compressor. There are exceptions, such as a compressor with a busted valve and excessive frictional drag, possible, but not a likely scenario.

Odds are that you have a stuck reversing valve. You also have a restriction where the liquid line temperature drop is occuring. If the compressor was recently replaced, then the system could be contaminated due to a previous severe burn-out.

Are you sure this is an R22 system? If you put R22 into an R410a system this will also produce high suction and low head.

[rmihvacr]

Assuming a commercial application and assuming a Carlyle compressor is installed (typical of carrier commercial heat pumps) amp draw could be misleading, although if you are stacking liquid the amp draw will decrease. These compressors typically have an un-loader. Carlyle and/or Carrier use 2 different types of un-loaders: Suction cut off and hot gas bypass. If the un-loader is in the unloaded position the amp draw will be reduced. Both of these un-loaders are mechanical only (no electrical control). With awkward pressures in this system I would expect it to be unloaded. This however should not cause the refrigeration effect exiting the condenser. The liquid you are producing with condenser is flashing (due to pressure drop) somewhere prior to your cold liquid line.The factory typically installs a drier inside the condenser and every inch of high side piping should be examined to verify no drier restriction. Locate the exact spot this refrigeration effect is occurring and you will have found the restriction. Carrier also uses a hot gas injection line to bottom of accumulator to promote oil return to compressor, examining this injection circuit is recommended as well