york 5 ton low suction line pressure

[greenhornBC]

hello,

Just installed a czb060 (5ton) york affinity ac system and 5 ton air handler. There is roughly 50ft of lineset, no harsh bends or curves. I added 1 lb 7 oz to compensate for the 50 ft of line. When the ac first fired, it shut off after 4 seconds. I found the low pressure switch to have been tripped. The suction line pressure dropped from 0 lbs, while the high side remained at 200lbs. The system has never been run before this. I recovered the r410 and ran nitrogen through the system to check for any blockages. (Nitrogen was kept at 2 lbs in the lines during brazing). At this point I am being told to switch compressors, since the unit is still under warranty. Any ideas if this sounds correct? I cannot under stand why the compressor cannot draw any refrigerant in. The system has no leaks, and was pressure tested and vac tested.

[greenhornBC]

also note, the bottom half of the compressor started to frost

[Gary]

Sounds like an evap airflow problem to me.

[greenhornBC]

hey gary,

the unit only ran for 4 seconds. the air handlers have the correct TX valve installed. The unit is not able to draw suction, nor create any pressure.

[greenhornBC]

the low pressure switch is being triggered, because there is no pressure in the suction line, thats what my gauges tell me

[Gary]

the low pressure switch is being triggered, because there is no pressure in the suction line, thats what my gauges tell me

No... your gauges tell you a number. What is that number?

[greenhornBC]

the suction line was at 50, and dropped to 0

the high pressure sits at 200

[Gary]

So... the pressure dropped 50psi in 4 seconds? Yet the bottom of the compressor is frosting?

If it is dropping that quickly, then there must be a closed valve somewhere. Does the system have a liquid line solenoid?

[greenhornBC]

there is a solenoid on the high pressure line. I am sure its working as it was warm and seemed to be buzzing. Also when I have experienced a solenoid to have failed, would that cause high pressure? There are no solenoids on the suction line.

[greenhornBC]

to me it seems as if the compressor cannot draw any refrigerant in, hence the low pressure. People have told me that it sounds like the suction line is blocked or kinked, but I have found that to be false.

[Gary]

Is the line warm on both sides of the solenoid?

Is the arrow on the solenoid body pointed in the direction of flow?

[Gary]

Where are you measuring the suction pressure?

[greenhornBC]

yes the solenoids are flowing the correct way.

I am hooking up at right at the outdoor unit.

Would a faulty solenoid on the high pressure side, trigger low pressure? I have found that when a solenoid fails on the high pressure side, it causes high pressure, due to the refrigerant not being able to flow.

[Gary]

I am hooking up at right at the outdoor unit.

Are the shutoff valves at the outdoor unit fully open? Backseated and then cracked open for gauge port?

[greenhornBC]

hey gary,

yes the valves are fully cranked open.

[Gary]

The valves should be fully opened and then turned in one turn to open the gauge port.

The real puzzle here is the frosting compressor. Did you charge the refrigerant though the suction port?

[yorkie10]

Is your pipe sizing correct, too smaller liquid line will restrict flow and hence starve expansion device, assuming no elevation difference and an equivalant length of 100ft liq line=1/2", dis line 7/8"

[greenhornBC]

hey yorkie,

the units are almost on the same level as the outdoor unit, maybe +- 1-2 inches...

There is one place where the liquid line goes has a couple 90's and one or 2 45's in a 1ft section, can this cause a starvation on the liquid side?

[greenhornBC]

for 5 ton I always use 3/8" liquid, 7/8" suction loine

[greenhornBC]

faulty solenoid....

easy fix!

unit was never ran, nor could the r410 pass,,,so there was no r410 in the suction line

thanks