404a freezer

need some help here. i have a 404 freezer walk in box that is giving me trouble. The unit is operating 18/260 psig on initial start up. when the fan kicks in pressures rise to 25/270 psig. while operating, the first row that is fed by the distributor nozzle start forming a snow blanket, causing my airflow to lower and loss of air flow eventually. The first row of the evaporator remains snowed back to the distributor nozzle, the remaining evap rows are dry. I replaced the expansion valve and installed a new frost termination/fan activation switch. Same results. The condensing unit is air cooled with a head master valve 180 psig. The valve is open to the condensing unit without signs of leaking. sight glass is clear.
any suggestions as to what this may be?

It sounds to me that maybe your TX valve and distibutor may not be matched correctly.

Describe position of TXV and distributor (or make photo) and how much apart they are (in cm).
Distributor must be positioned vertically. What is evaporator capacity and TXV make and model number? Orifice size?
Take bulb of TXV in your hand and see if that make any difference after while on frost pattern of evaporator.

the txv is flared sporlan fse 1 1/2 ton - txv was replaced yesterday and dial inside distributor matched for 404A on installation. the unit worked fine for 2 years. its driving me crazy that only the distributor line and first row of the coil gets snowy and the rest of the coil is dry of snow and seems normal. I even blew out the evaporator. I thought there even may be something wrong with the single fan motor not blowing enough air but its rated for 1.4 amps and drawing 1.5 amps. I'm stumped.

Over charged???

head pressure is too high mate. R404a massively loses effciency after 250 psi.should be around 215-230..
Your evap coil isnt fully flooded and you have very low suction pressure so id say you have the wrong size orifice or a blockage.

Air on the system due a possible recent service? The presence of air increase the discharge pressure.
Blow the R404A circuit with nitrogen. May be as licencetochill said a blockage in almost circuits.

what make evap is it?
some have a orifice in the distributor.
ie an orifice for gas type i think buffallo trident is one of them.

is may be a possibility or is there any kinks in the distributor.

Assuming you have fitted a TEV and not a TV. Firstly check your superheat across the coil. This will confirm a starved coil so then check your valve it may be partially discharged or filter blocked.Also the external connection should really be after the bulb

is there a heat exchanger by any chance in the loop? they can implode,a dodgey CPR ? just a alternative to the TX.:)

Sound as you got a restriction somewhere in the system.

What you describe is typical for such situation

Is the txv externally equalized. If so make sure the external line is clear. On a freezer a mop valve is the way to go also.

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Originally Posted by premoctane

need some help here. i have a 40
4 freezer walk in box that is giving me trouble. The unit is operating 18/260 psig on initial start up. when the fan kicks in pressures rise to 25/270 psig. while operating, the first row that is fed by the distributor nozzle start forming a snow blanket, causing my airflow to lower and loss of air flow eventually. The first row of the evaporator remains snowed back to the distributor nozzle, the remaining evap rows are dry. I replaced the expansion valve and installed a new frost termination/fan activation switch. Same results. The condensing unit is air cooled with a head master valve 180 psig. The valve is open to the condensing unit without signs of leaking. sight glass is clear.
any suggestions as to what this may be?

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Sometimes air on system can create a restriction on the TXV this can be happening to this system.

Quote:

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Originally Posted by licencetochill

head pressure is too high mate. R404a massively loses effciency after 250 psi.should be around 215-230..
Your evap coil isnt fully flooded and you have very low suction pressure so id say you have the wrong size orifice or a blockage.

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I disagree completely.
1. How you conclude that HP is too high? You don't know the ambient nor the air on of the condenser.
2. How can a refrigerant - R404a in this case - lose its efficiency?
3. Why at a sudden should it loose efficiency if the HP raises from 230 psi to 250 psi?

I agree with the 2nd part of you post.

Quote:

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Originally Posted by Chewman

Over charged???

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Should this gives then all these phenomenas? I doubt.

Quote:

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Originally Posted by Lastguest

Assuming you have fitted a TEV and not a TV. Firstly check your superheat across the coil. This will confirm a starved coil so then check your valve it may be partially discharged or filter blocked.Also the external connection should really be after the bulb

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What difference should it make if a TV instead of TEV?
The SH over the coil can be OK but the coil can partially be starved.
Why must the ext. connection be installed after the bulb? Isn't it even better that it is installed just the opposite way? Giving the fact that you speak about TEV an TV, I assume you're referring to Danfoss valves?

To summarize:
Air in the system will not starve you coil partially, it will increase HP and discharge temperature.
No or wrong orifice in distributor.
Distributor not facing up or down.
Blocked capillary tube from distributor to coil.
The TEV can't be the problem, all rows should then be starved or flooded.

You have to measure every circuit in your evaporator on the same place to see which circuit is blocked.

Other possible cause: once circuit has no load (ice on that circuit, perhaps on the inside of the evaporator) or the fan isn't blowing on that circuit. This not loaded circuit is flooded and the TEV bulb senses this and closes therefore all the other circuits, trying to maintain the SH of this one , almost not loaded circuit. Resulting in one circuit which seems working but on a very low evaporating temperature because the evaporator is working on only one of its partially loaded circuits.
This phenomena happens when one row is freezing horizontally, mostly the upper or the lower part of the coil

i agree we need to know the ambient temp ,but there seems to be a inbalance between the suct/dis pressures,wheres the man with the answers anyway.!

sounds to me like you may have oil choking part of the coil or distributor.
check the iol level in the compressor.

hi u said that u have changed the exp what about filter drier