High Head Pressure

[kengineering]

Its a simple self contained, vertical, grab and go conveinence store cooler. Ambient OK, 3/4-hp , 404A, TXV.
Original call, Off on high head. Condenser clean, fan motor correct rotation and the blade is ok. Not knowing the previous history, over the past several months we have recovered and evacuated the system and recharged. The TXV power-head was changed. Everything is fine for a while. Then a week later high head again. Fearing an overcharge a small amount of refrigerant was purged and the Head came down but the coil appeared starved. The refrigerant was then introduced slowly to again flood the coil and the Head shot up abruptly.

Any Ideas?

Thanks, Kengineering

[AlexG]

Air inside circuit?

[Brian_UK]

What is the superheat like?

[monkey spanners]

Does the txv have the correct orifice? Has someone fitted a txv to a cap tube system and not fitted a reciever? Is the drier blocked?

[chemi-cool]

R-404 tends to "burn" and act funny sometimes.
you can replace it with r-507 without changing anything but the drier.

[kengineering]

As far a s non-condensibles "air" in the system or a blocked drier. The charge was dumped filter drier changed and recharged...It was never a cap-tube and there is a receiver. Will have to get the tech to check the SH. The orifice may be next..
R-507 hmm never used it.

[sterl]

Whats the suction pressure like while all this is going on?

it sounds like the TXV is not feeding which after a week of running good then sounds like upstream restriction like the rest of these folks said...But what should go with it is a low suction.

[Glenn Moore]

What pressure is the HP switch set to trip at?
What is the normal running discharge pressure
How much liquid subcooling is there.
A lot of small condenser fan motors have internal overload protectors built into the motor windings. It may be that the fan bearings are getting tight partially seizing causing the fan motor to run hot and at a slower speed and tripping on its internal overload protector. Once it has tripped and cooled down it again runs OK for a while.
I experienced something similar to this on one manufacturers condensing units. The units had the discharge pipe from the compressor to the condenser inlet run just underneath the condenser fan motors. The heat from the discharge pipe caused the fan motor to trip on its internal overload and then the compressor tripped on the HP switch. The solution was to simply push the discharge pipe down away from the fan motor, no further trips.
Check the RPM of the fan motor with a rev counter
Changing the TEVs orifice would have little or no effect to the discharge pressure

[kengineering]

All great replies and I thank you all. I had the service company leave the front and rear grills off and it ran fine. Seems the manufacturer produced this unit with a poor design for the intake and discharge grill. The "free grill area" just would not let it breathe freely enough..

Sometimes the answer is right in front of you.. Happy Easter and Passover to all those observing...

Kengineering