Fluctuating refrigerant pressures

[nortonma]

We were doing a start up on a Bryant A/C system that we installed today and after 5 minutes of running the low side was fluctuating between 110 to 125 psi and the high side was fluctuating between 250 to 290 psi. What could be causing this.

Evaportator has a TXV
Return 73
Supply 55

We have been installing Bryant for 5 years now and this is the first time that this has ever happened. The customer had to leave for a wedding today so I did not spend much time on diagnosing the problem.

[Rubio480]

Was the system properly evacuated? Purge nitro while brazing? Vacuum to 500 microns? Purged hoses before adding 410a to compensate for lineset length? Is sensing bulb at evap insulated? Is entire lineset insulated?


We all make choices, but in the end our choices make us.

[gravity]

Non condensibles, refrigerant wasnt added as 100% liquid, or txv hunting

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[nortonma]

System was properly evacuated and purged while brazing.
How do you test for non condensibles

[yaytech]

is this 22 or 410 ?

[nortonma]

410

[CircusEnvy]

If it's fluttering, it could be a blockage somewhere.

[Brickey]

As always we need a little more info please. Does this unit have the new LG scroll compressor in it? What is your sub cooling and superheat? How fast does the head pressure change? How fast and how much is the sub cooling changing?

[dachipsta]

I had to replace a locked up compressor on a rheem split a couple of years ago. Once I had the new compressor in and started it up, after a few miinutes of running it was doing the same thing. TXV was the culprit. New valve, and system was running fine.

[MIREMEG]

If you have done everything right look at your duct work. If it is under sized or if you can hear the air whooshing-fluctuating it could be bad or undersized duct work. Remember your txv reacts to temperature on suction line. Suction line temperature is based on evaporator coil temperature. If the air is fluctuating due to effective duct, so will your pressures.

[MIREMEG]

I ment defective ducts. Sorry I'm using my phone

[MIREMEG]

Terminology. Fluctuating or whooshing air is usually caused by a blower motor hunting for the right static pressure and air flow.

[Lenox HVACR]

could be liquid sluggin that happened to me once and that's what it was but that was just once not really to sure though