Manitowoc Question

[jamesgriffin]

Manitowoc model Qyo455a
charged with 404a

keeps going out on freeze timer. pressures showed 67 psi or (roughly 28 degree) saturated evap temp... and 276 head pressure (120 degrees) ambient temps was 75. unit had obviously been worked on before but by whom? was running a little bit high head pressure and I wanted evap a little colder. Assumed unit because of high pressures was overcharged. check superheat and found 35 degrees superheat and the compressor was hot. I cleaned condenser coils, and then pulled 36 0z of 404a from unit... manufacturer's recommended charge was 24 0z. After pulling vacuum to 200 microns I then recharged system with 24 oz of 404a. I then checked to make sure there was an adequate water flow across evaporator... everything appeared normal... started unit up and nothing appeared to change.., except we were now running about 25 psi lower on head... however the superheat at compressor was through the roof? Unit just won't pull down quick enough. Unit will make ice but it takes like 40 minutes to make a sheet and after 3 times of running so long between harvest cycles it will shut down. I suspect that the valves in the compressor are shot.... from running overcharged too long? When unit shuts off ... the suction pressure immiediately shoots through the roof like all the liquid is flooding back into the low side? Could I be missing something else here?

[hvaccop]

what is subcooling and superheat with proper charge? Could be bad TXV or restricted drier if you have high superheat and high subcooling.

[the mojo]

Check TD over the evap and also confirm non-bleeder through HGDV. 5 minutes into freeze.

[keywest]

make sure the liquid line solenoid is not sticking,check the txv,make sure the dump valve is not stuck open,and water inlet valve.

[wannafreeze]

Check TD over the evap and also confirm non-bleeder through HGDV. 5 minutes into freeze.

would you ensure "non-bleeder" by crimping the line?

[the mojo]

Two K-12 probes on either side of the HGDV. Example: Discharge line while running 120 *F. 4 " past 90*F can = high suction. Reduced capacity and long freeze time.

[jonbailey19808]

Dont assume the compressor is bad. What you need to do is fill out a refrigeration analysis chart and it will tell you exactly waht is wrong with it.

Here is the link.


http://www.manitowocice.com/Service/AnalysisCharts.asp

You want to print out the Single TXV version. Fill out the chart. Also if you need what pressure are supposed to be you can print that out from the same website under Service tech handbooks.You dont

If this does not help call 1 800 545 5720

You dont want to needlessly change a compressor. Your choices are: Hot gas valve leaking through, TXV flooding, Compressor ineffeicent.

[jamesgriffin]

filled out refrigeration analysis chart and then it checked out for bad compressor. put new pump on and charged up today... she is making ice like crazy.. I was 95 percent sure comp was toast because when comp shut down almost instantly all the pressure would go back low side. when unit started you had 250 psi on the low side and it would never pull down past 66 psi.... but I just wanted to ensure I had elimanated everything thing else before I made condemed a compressor. thanks again....

[jonbailey19808]

Good job James! You nailed it!

[refertecbd]

Q modle manitowocs are famos for txv failures. That high SH sounds like a restricted valve