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Brew
18-08-2017, 06:15 PM
Currently working on a Foster Fridge FPS5HR, a 5 door prep Fridge in a Restaurant. Initial inspection showed Evap at room Temp (25C), Condenser/Evap was reasonably clean, All fans operating, System calling for cooling, Comp Running. Chucked a Gauge on the Comp Head, 0psi, Threw two line taps on where I could, one on the Condenser Discharge showing around 90psi. One on the Comp Suction showing 0psi.

Initial thoughts were low on Gas, So I weighed out 760grams (supposed to have 800g, guess some stuck in oil), Chuck 800grams of fresh R134a in. Still no Joy. Chucked in another 100grams, just for good measure, no joy.

Still the same, all valves equalise on Gauges when the system is off, showing there isnt necessarily a blockage in the capillary. When I power up, the Condenser discharge goes up to 90psi. Comp Head matches the suction into pulling a Vac, which I presume goes all the way back to the evap coil.

So I was convinced this must be something to do with the capillary, perhaps some moisture build up that it cant shake, and it only lets a small amount through, I reclaimed the gas, Chucked Nitro through it several times, Triple Vac'd, regased, still no joy.

So today I returned to the job, I decided to replace the capillary, perhaps a bad call, but I cant see how this can necessarily be a compressor fault as its pulling a vac on the suction and evap discharge does increase when the comp kicks in on startup. So I replaced the capillary, taking care to keep the line on the top of the pipework and away from any potential oil buildup in the system. Threw on a filter drier. put it together. [edit] I did a pressure test in through the condensor discharge and the resulting nitro came out through the Comp Suction, suggesting I didnt block the capillary by accident. Vac'd for an hour, Regased, and still no joy, system is still at air temperature. Suction pulling a vac and 90PSI on the Condenser discharge.

I can see some slight frosting initially buildup just before the capillary the evap inlet is still ambient.

Hopefully im not being a nonse here but im not a complete expert in the trade still much to learn! But all I can consider now is that the compressor is not providing enough PUSH on the discharge to get the gas through the system. So essentially a Compressor change.

Any thoughts?

Thanks in advance

cadwaladr
18-08-2017, 06:36 PM
It does sound like the compressor is weak,I would have expected head pressure to be higher

Glenn Moore
18-08-2017, 07:18 PM
Sounds like a blockage still. Suggest removing the gas charge unbrazing the capillary from the evaporator and blowing nitro into the discharge pipe to see if it blows through the condenser and out the capillary. By blowing the nitro into the discharge line the discharge valves in the compressor should stop the nitro going back through the compressor .If the nitro doesn't appear from the capillary either the cap is blocked or the drier is. You may have blocked the drier or capillary when you brazed it together it's very easy to do due to its small diameter .Ive seen the copper spun driers blocked with brazing material but cap tubes are even easier .
When you see this fault on a cap tube system use a hair dryer, paint stripper or a low flame to warm the area of the evaporator where the cap tube enters probably 3-5cms along the evaporator inlet tube warm this area while the compressor is running within a short time if there is an ice blockage the heat will melt the ice and you will hear the refrigerant spraying from the cap tube into the evaporator , normally if its moisture the blockage will quickly reform and the compressor will again pump down, if it's dirt in the drier no change will happen good luck

Brew
18-08-2017, 07:30 PM
Thank you for the reply Cad!


Sounds like a blockage still. Suggest removing the gas charge unbrazing the capillary from the evaporator and blowing nitro into the discharge pipe to see if it blows through the condenser and out the capillary. By blowing the nitro into the discharge line the discharge valves in the compressor should stop the nitro going back through the compressor .If the nitro doesn't appear from the capillary either the cap is blocked or the drier is. You may have blocked the drier or capillary when you brazed it together it's very easy to do due to its small diameter .Ive seen the copper spun driers blocked with brazing material but cap tubes are even easier .
When you see this fault on a cap tube system use a hair dryer, paint stripper or a low flame to warm the area of the evaporator where the cap tube enters probably 3-5cms along the evaporator inlet tube warm this area while the compressor is running within a short time if there is an ice blockage the heat will melt the ice and you will hear the refrigerant spraying from the cap tube into the evaporator , normally if its moisture the blockage will quickly reform and the compressor will again pump down, if it's dirt in the drier no change will happen good luck

Thanks for the reply Glen, I in no way mean to discredit or devalue your response, just a question though.

If I apply Nitro on the condenser discharge, and it comes out through the Compressor Suction, Surely its not a blockage in the capillary or the drier?

That said ill try applying heat to the evap inlet, see if that makes a difference.

[EDIT] Just notice I didnt actually put in that I did that, I was thinking it! Just didnt put it in.. FFS

Glenn Moore
18-08-2017, 07:54 PM
Brew
By putting the nitro into the discharge line the compressor discharge valves will be pushed closed and no nitro should come out of the compressor suction,so the nitro can only go one way,i.e. through the condenser ,the drier and the capillary tube if it doesn't you have a blockage

Brew
18-08-2017, 07:59 PM
Brew
By putting the nitro into the discharge line the compressor discharge valves will be pushed closed and no nitro should come out of the compressor suction,so the nitro can only go one way,i.e. through the condenser ,the drier and the capillary tube if it doesn't you have a blockage

Got you, thanks Glen, yes I did that, so I guess theres no blockage, unless moisture built up later

tonyelian
17-09-2017, 03:30 PM
hi dirty condenser replace it

monkey spanners
17-09-2017, 07:10 PM
If the compressor was weak (as in not pumping well) you would have a higher than normal suction pressure not lower.
Head pressure is a function of ambient temperature/condenser cleanliness and how much refrigerant you are trying to condense, so low flow into the compressor will result in low flow out the discharge which effectively makes the condenser oversized and consequently the head pressure will be lower than normal.
Sounds like a restriction, most likely either the drier or capillary tube.
Its possibly to have a partial restriction, so the system will equalise when turned off, it just won't cool well.