TXV is hissing - what's that mean?

[Poodle Head Mikey]

Regular long-time customer calls and says that the walk-in box is making a hissing noise - inside the walk-in. It's been hissing for a few days. the hissing noise comes from the end of the evaporator where all the pipes connect he says. The box temperature is fine. The hissing continues for a little while if the evap fans are shut off. And he says that it didn't make the hissing noise before now.

The sightglass is full.

What would make a new hissing noise?

Any ideas?

[pelican]

Is there a head master on the condensing unit?with the temperature change it could be bypassing the coil and a little low on charge,compressor runs warmer too i have found.

[Poodle Head Mikey]

This is a frankenstein system with the wrong indoor condensing unit out on the roof, cond. fan cycling only, with the incorrect compressor installed on it, and cobbled to some mis-matched evap. coil with the wrong TXV.

The hobo who created it thankfully died and they called me.

5' by 6' 40 degree walk-in. Original issue: in hot weather, with a warm box, say; after a power failure, the high suction would start the compressor cycling on the O/L and that would never stop until you cooled the compressor externally.

I approached it in steps: first I fixed all the elaks and installed the correct TXV and used a pressure limiting valve to limit the pull-down amps.

That worked so I never went any further. I will do it all over properly when it fails but it's been years now. <g>

PHM
-------

Is there a head master on the condensing unit? with the temperature change it could be bypassing the coil and a little low on charge, compressor runs warmer too i have found.

[KB Cool]

Who said the sight glass is "full"? The customer? If so its probally empty.

[grasshopper1]

Who said the sight glass is "full"? The customer? If so its probally empty.

lol aint that the truth!

[Poodle Head Mikey]

I know from experience that this unit loses temperature badly when the sight glass is just slightly less than half full. <g>

PHM
-------

Who said the sight glass is "full"? The customer? If so its probally empty.

[pelican]

sometimes you have to settle with what ya got wish we could make em all perefect

[steve wright]

Have you checked the suction line heat exchanger if it has one? Sometimes a liquid to suction rupture can cause noise.

Steve

[markettech]

Have you checked the suction line heat exchanger if it has one? Sometimes a liquid to suction rupture can cause noise.

Steve

And a big ball of ice on the head of the pump

[Poodle Head Mikey]

This time I found the roof so warm (black rubber) and pleasant that after I attached the gauges and temp probes I was just sitting there watching the clouds overhead and the young ladies parade around the bank on one side and the hospital on the other, when the 35W unit-bearing condenser fan found began to first emit an odd noise and then eventually stop turning. Right after that the head pressure went to over 400 and the compressor shut itself down.

So I guess that was the "hissing noise" the customer was hearing. <g> What I had been hearing was the normal TXV sound.

Weirdly; the condenser fan motor looked and felt fine. Turned smooth and free and had oil still in the wick. Even with no blade attached it would run for maybe twenty minutes in silence, then start making an off noise, and then stop turning. And even at that point the shaft was perfectly free. I have never seen that happen with those simple little motors before. 99% of the time they are stuck and only extremely rarely free turning but won't run. But this one was intermittant.

And the 400 lb. liquid feed was making the TXV "hiss". <g>