Walk In Freezer Issues

[texas64]

Hello,

I sent one of my techs on a late evening service call for a walk in freezer that wouldn't pull down below 16deg F. It appeared to be a dirty condenser coil and he cleaned the coil. The box at this point was at 22deg F and pulling down. He returned the next morning to check on it and found the condenser motor seized and the unit cycling on the high pressure control. He replaced the motor and the box still won't pull down to zero. He also bypassed the headmaster by cutting and capping off the compressor discharge line going towards the headmaster. I told him to replace the refrigerant after recovering and evacuating with virgin r404a. I didn't want there to be a non condensibles issue. He even installed a higher rpm motor(1075rpm now 1625rpm-measurements are with 1625rpm motor) Here are the relevant temps in fahrenheit.

Cond air on: 91
Cond air off: 115
Liquid line at txv: 138
Suction line at 12" from compressor inlet: 42
Suction line at outlet of evap:
Suction pressure: 38psi
Liquid line pressure: 360

This condenser is 3 years old made by Trenton.

[texas64]

Almost forgot. Discharge line temp leaving compressor: 182

[Tayters]

Not familiar with the set up there but the air on the condensor is high and the dT across it is bordering on the high side as it the condensing temperature. Subcooling at the TEV is non existent.

Are you sure the condensor is clear? Might need blowing out with OFN.

Cheers,
Andy

[Rob White]

.

R404a will not last long if the condenser was blocked and then the cond fan failed.
R404a has a critical temperature at about 70 degC (about 160 degF), if the refrigerant
runs near to that temp for too long it breaks down and thermaly decomposes.

After the refrigerant is replaced if it runs down to temp then the refrigerant has decomposed.

If the gas smells burnt that is a good indication it is damaged.

Regards

Rob

.

[Rob White]

.

Another thing with R404A is it is a Zeotropic and made up of

R125 / R143a / R134a at 445 / 52% / 4%

If it has ever had a refrigerant leak and "topped up" then the condenser
becomes blocked it agrevates the refigerant even more and it decomposes.

Regards

Rob

.

[texas64]

I was concerned with issues regarding the refrigerant so I had him recover and replace with fresh R404a, but there were no odors other than that typical smell of refrigerant. There have been no leaks since 3 years ago and no top offs. But I still had him replace refrigerant just to eliminate that issue. As far as ambient temps, 91 degree fahrenheit isn't a big deal I don't think. We get to 105 degree occasionally here. Yes, you're right, subcooling is dead. That's what I don't get. I will have to go out there and see for myself. This a high humidity area-right on the beach at sea level. I'll post evap temps shortly as he is headed there now. Thanks

[Tayters]

Yes agreed, ambients of 90 shouldn't cause a problem if the system is in good order. Not used to such temperatures here across the pond.:D

Seems to me the condensor can't reject enough heat therby raising SCT and SST and lowering subcooling. With those ambients discharge pressure should be no more than the 320pisg mark. Even that I'd feel is a tad on the high side, I'm more used to seeing 250ish even in stuffy kitchens.

Cheers,
Andy.

[al]

You mention it is by the sea, has the condenser started disintegrating, or while cleaning the coil have the fins been crushed? Have you checked the pumping of the compressor, could be that the blown motor caused a compressor issue, fairly common.

al

[padraic]

just by the off chance did he put the fan blade back on the rightway round... worked on a unit lately that another company was at and they had changed condenser fan motor but system wasnt running great... so we ended looking at it.. they changed gas adjusted valves etc etc... but when we checked it there was a very bad airflow off condenser and high discharge pressure... so we turned around blade and running perfect since...

[Magoo]

Hi Texas,
the discarge pressure at 24 bar is way too high, with high load and high ambients I dont charge to a clear sight glass,but discharge and suction pressures, (19bar /275psig 45'C max discharge) plus the 50 % increase in condenser fan speed could be working against you as well, the air dwell time in condenser coil would be reduced and lower heat exchange.

[cadwaladr]

24 bar? way way too high blockage wrong size condensor?blocked air flow across the condensor what is the h/p set at?