I have a client with a walk-in freezer on R404a. It was installed about 2 years ago and spent the first year being constantly "repaired" by the installers (not us). After about a year of them messing with it I was called and found a sticking solenoid valve and it was a touch short of gas. Since that visit it has worked perfect and held -18ºC. A couple of weeks ago it got really hot here and the temp went up to -12ºc, i got there and found the condenser blocked up with dust. I gave it clean and the next morning the temp was back to normal for a couple of days at which point it started to climb again. Got there and found the evap heavily iced up and blocking the fan from running. Defrosted the evap and ran it up again. It got to -14ºc and wont go lower than that.

I took some readings yesterday,

L.P. 18psi (taken at the condensing unit)
Suction temp 1: 4.2ºC (as above)
Suction temp 2: -20.1ºC (taken inside the room about 1 meter from the expansion valve)
Air On cond: 27.9ºC
Air Off cond: 31.9ºC
Liquid line temp: 32.7ºC (taken just after condenser)
Dischage Temp: 80.2ºC
Air on evap: -6.2ºC
Air off evap: -10.3ºC

The room was down to -14 when I took all the readings outside the box. I had to obviously open the door to get in to take the other readings, judging by the air on, the temp increased in the box to -6(ish) for the inside readings.


There is no port for taking a discharge pressure, or if there is it is well hidden. The condensing unit has brass service valves like you see on small split a/c systems. This is where the suction pressure was taken.

A few other things worth noting. The evap was even frosted all the way along. The expansion valve was completely frosted (quite heavily) and the liquid and suction line feeding it were also frosted. The gas smells burnt, which it didn´t last time I worked on it and the sight glass is full.

I think there is either moisture/blockage in the system or there is a problem with the expansion valve (which is externally equalised). Leaning more towards moisture/blockage as the valve is frozen up on both sides.

Opinions please?