catering freezer confusion!!

[4sac]

Hi all,
I'm an air con engineer but was asked to have a look at a catering freezer that was defrosting I turned up to find a completely blocked filter after clearing that the temperature immediately started to drop but only got as far as -4/-5 doesn't seem to be any other problems basically I don't want to fit a line tap if I don't have to. what I'm wondering is could the compressor hold enough heat from running with a blocked filter that the system is still running at too high a pressure to subCool. Basically is it worth turning it off completely for a few hours and starting it up once the compressor has cooled?

[4sac]

Filter was on the condenser btw

[Rob White]

.

You don't say what refrigerant it is, but if it is 404
they suffer from Refrigerant thermal decomposition
(the gas burns out) if the system runs too hot and
too long with a blocked condenser.

If the comp is ok it might be the refrigerant, the only
way to find out is with a set of gauges.

Rob

.

[Andy W]

With a filter on a condenser it could be a Polar or Apollo brand, if so and it is an upright freezer does it have an evaporator coil and fan or do the inside walls freeze up like a chest freezer and has a small circulation fan, if it is the latter then you have to give it time to pull down, also check the door is closing and sealing, I have had worn hinge pin bushes on these, in the past I have had to put a fresh charge of gas in these cabinets as after a while and a few blocked condensers working in high ambient conditions they tend to lose efficiency.

[4sac]

Thanks guy's, it is 404 and forced convection on the evaporator pretty sure thermal decomposition will be the problem here then.

[monkey spanners]

If it has got really hot, then the high head pressure that goes with this can break the valves in the compressor and stop it pumping, it may cool a bit but then stop at too high a temperature.

[r.bartlett]

probably the condenser is still blocked...

[joe-ice]

Put the line tap on it .You are looking for a diagnosis and agreeing a solution without even putting a gauge on it.

[Andy W]

Regarding condensers, fridge engineers don't need to be told this, the fins can look clean but deeper in the coil block can still be blocked, we can tell by just feeling the discharge and liquid lines, in this case get your air compressor or bottle of nitrogen on the job or if in a greasy kitchen it will need degreasing, fitting a line tap would be so simple and give you a window of the system.