Small Display Chiller

Hi

Hoping someone can help me with a problem I'm having with a display chiller that has been converted for R22 to R404a. (Fixed charged, capilary line)

Unit was running but not cooling, traced to a leak in the scharder service valve on the compressor. Reclaimed remaining gas, replaced filter/dryer, pressure tested and vac-ed down.
The name plate on the chillers says 500g of r22, so i recharged with just under 450g of r404.

Heres where the problems started, the case starts to cool and the suction pressure sits around 7 psi. Straight away there is frosting on the evapourator pipes where the capilary tube enters, and after half a day there is heavy frosting over 1/3 of the evapourator (fans are running as should) and the temp starts to climb.

Apprehensive to add any more refrigerant as I don't want to damage the compressor, but I'm scrating my head at what to do next??

Any help is much appreciated

Shaun

have you checked the supperheat and subcooling

whats your high side pressure asumeing correct capiliary and comp its short of gas 7 psi on r404a aint enough suction classic symtons its short if no hp port whats your run amps on comp

hi you mention that you switch 22 to 404 so you have to check cap tube matches the size of the compressor you have to provide more info such condenser air in & out temp any way cause its a cap system u cant measure high side pressure at liquid line before the drier to calculate ur sub cooling unless u fit an access valve there is more than one cause for what you have describe 1-too long cap tube or restricted 2-small compressor

Hi
Thanks for the replys.

The chiller has been written off by the company i work for so I'm using this as a learning project to get it up and running again.

There is no high side valve, i will add one though.
The compressor is a L'Unite/Tecumseh aez9440z which is a direct replacement for the r22 model that was in the chiller.

I have not changed the capilary so from doing some reading am I right in saying that it will now be too long?
If so how do I go about working out the correct length and internal diameter?

When looking at the superheat side of it, on a capilary system is the temp taken at the evapourator outlet and compared to the pressure/(pt temp) at the service port on the compressor?

Again thanks for the help :)

Shaun

Check the specific density changes between 22 and 404, 404 has to operate at higher discharge pressures. Around 38 > 40'C SDT.

Hi

Since my last question i have changed a few things on the display chiller.
I have added a hi side access port and reduced the capilary length from 1035mm to 650mm (0.8mm id)

I regassed the system, i now have a much lower temp but still some problems.
Low side 11.9psi, high side 158psi
Suction pipe temp 3.2degc
Condensor pipe in 30.5degc, out 19.5degc

My pressures are still too low (i think :) ), i get about 4 hrs of the chiller cycling around 2-4deg before frosting on the evapourator.
Pretty confident it is not a gas quantity issue.

Any pointers as to where i should look next would be great!

Shaun

Shaun,
R404A at 158psi got a bubble point of 23*C, you having a liquid line temp of 19.5*C are giving us a sub cooling of only 3.5K.
This is on the low side and it would be worth adding a bit more refrigerant, if only to see what will happen.

@ 12psi R404A's dewpoint is -32*C, with a pipe temp of 3.2*C the superheat is a massive 35K.
This means not enough refrigerant is circulating in your system, either due to a lack of refrigerant or too much restriction in the refrigeration circuit.
So if this remains this high after the sub cooling been raised to about 4-6K, I would say that your capillary tube is too long.

Happy hunting.

:cool:

The way i see it, a .8mm id is too small in the first place. (SP2) Should have around 45 psi on R404a so evaporator does not run too cold. Cutting cap tube any more can lead to wild pressure swings. Currently searching old files to see what i can dig up for you, don't hold yr breath.