TXV hunting in a walkin cooler

[dkemper]

I've an R22 walk in cooler that's not keeping temps real well. Target temp is 34°F or 1°C. This cooler has NO history of ever running correctly. The cooler will recover well to it's best temp even when subject to a sudden and heavy heat load, but never does fully come down to temp.

I've verified the thermostat is set and working correctly. Pressures look good for R22 medium temp, sight glass is clear but I'm seeing excessive hunting on the expansion valve, from 1°K to 10°K.

A quick inventory of the cooler shows a 26.6kBtu/h evaporator, a 28.5kBtu/h condensing unit and a 18kBtu/h expansion valve.

I'd have expected an over sized valve to have hunting problems, but this valve appears to be undersized for the application.

First thought had been to simply replace the thermal element, but I'm leaning towards replacing the whole valve.

Have I missed something obvious or does it look like I'm on the correct path?

Thanks!

[Jase]

Try repositioning the TXV phial on the suction pipe @ the cooler.

Regards
Jase

[PaulZ]

Hi dkemper
What are the operating pressures?
If the valve is too small and the evap has been starving for a long time the evap could be oil logged as this system is on R22.
Has the compressor had oil added regularly?
Probably would be best to replace the valve with the correct size and the watch the oil level in the compressor, if the evap is oil logged.
Let us know how you go.
Paul

[Bones74]

Still no response????

[Pooh]

What is the measured superheat? If the valve is to small it will not be able to modulate properly the valve will be fully open but not letting enough liquid into the evaporator to get correct cooling. Fit the correct sized valve and you should be OK.

Ian

[jose regueiro]

at +1Cº need defrost, electric or hot gas

[Gary]

What are the evaporator air in and air out temps? Insufficient airflow would reduce the heat load, which could cause the TXV to hunt. In effect, the valve would be oversized for the actual load.

If the system has never performed correctly, we might look for something like wrong fan blades or blades installed backwards, backhanding rather than cupping the air. If the fan motors are 3 phase, they might be running backwards.

Does the system have an EPR or SORIT valve? If so, the setting may be too high, limiting the load.

[Toosh]

Hi, one question I would ask, is it a holding freezer or a pull down one it seems to me that its sized as holding freezer and has trouble pulling the temp down. only a thought

Regards Toosh

[chillyblue]

Hi.

If the the evaporator and condensing unit are correctly matched and the TEV is undersized then you must have bad heat exchange at the evaporator!! or poor airflow, or a internally coated evaporator coil, not allowing optimum heat exchange.

CB

[Gary]

Indeed. Airflow problems can cause refrigerant flow problems, but not vice-versa.

That's why a logical trouble shooting procedure would have us checking for and correcting any airflow problems before putting our gauges on the machine.