telling if a system is short of gas

[hammy]

Hey,
If a split a/c system has a vertically mounted sight glass should it be full to the top when demanding for cooling. At present its only has liquid about 1/3 of the way up. I know you shouldnt judge by sight glass alone but just trying to get a rule of thumb

The condensor coils are choked and im about to get scaffold to clean them...would this affect the sight glas bubbling

The evapourator was originally iced up completely too

Any help much appreciated

[hammy]

just to add the unit seems to ice up just at the front of the evap at the moment

[chemi-cool]

Run the system after cleaning the condenser and then check the sight glass, aqd refrigerant and check pressure in low and high side.

[marc5180]

The evap is freezing up because there is not sufficient airfow passing over the coils. You need to clean both coils to be sure of correct airflow.

[casstrig]

the bubbles you are seeing aredue to flashgas clean both coils and check again.

[hammy]

hey folks cleaned the condensor coils and no change...but got the following

When ac unit is started almost immediately the front of the evaporator has ice on it

R59…using the r22 scale the lp pressure is 0.4 bar and the hp is 8 bar. The 0.4 bar equates to –35oC on the temp for r22. As this is an ac split this is far too low and all these points indicate the unit is short of gas….don’t they

The sight glass has practically no level but then fills half way as if its pulsing. The liquid line to the evap and the return to the compressor both feel about the same temperature.

Is the above way of thinking correct. Im just learning fridge at the moment…as you can tell J

Thanks in advance

[superswill]

hey folks cleaned the condensor coils and no change...but got the following

When ac unit is started almost immediately the front of the evaporator has ice on it

R59…using the r22 scale the lp pressure is 0.4 bar and the hp is 8 bar. The 0.4 bar equates to –35oC on the temp for r22. As this is an ac split this is far too low and all these points indicate the unit is short of gas….don’t they

The sight glass has practically no level but then fills half way as if its pulsing. The liquid line to the evap and the return to the compressor both feel about the same temperature.

Is the above way of thinking correct. Im just learning fridge at the moment…as you can tell J

Thanks in advance

0.8 bar suction sounds far to low! the 8 bar reading was it taken from the discharge (at the comp) or the liquid line? as was said is the indoor coil clean? what make of unit is it?

[marc5180]

Yes the charge looks low if the 8 bar measured was the the discharge. Is the evaporator fan running?

[hammy]

sorry the reading of 8 bar was taken at the liquid line just after the condensor and the 0.4 from the suction...The evap is spotless and evap fan is running. the unit is an imi 80

cheers

[TRASH101]

The IMI splits tend to have a restrictor (field installed) on the liquid line directly after the service valve. This can sometimes choke, it can be difficult to check without stripping but if you have a large TD across the restrictor then that could indicate a blockage. A discharge temp taken at the coil entry would be handy and confirmation that the fan speed controller is operating properly would help also.

[TRASH101]

P.S. is there a drier and is it TEV or cap?

[hammy]

P.S. is there a drier and is it TEV or cap?

there is a drier and its cap

Thanks folks for your assistance. My job doesnt entail a huge amount of fridge breakdowns and fortunately im on the same systems all the time so I can learn them as i go.

Ive spoke to the manufacturer who have said the r22 pressures are 3 bar and 16bar. This unit has r59 in it

Are there any charts anywhere for knowing whether to charge as a gas or a liquid for each gas

once again your help has been very much appreciated

[Brian_UK]

If it is an IMI unit then it shouldn't have a drier in the expansion line.

Sight glasses can be misleading on IMIs.

As said above, check for a blockage around the restictor.

Recharge with the condenser fan at high speed, use the charging plug if there is one.

[GXMPLX]

Hey,
... just trying to get a rule of thumb

There is no better way than recover, weight, compare to manufacturer's data and recharge.

Symptoms of low charge are simultaneous low suction pressure, low condenser pressure, high compressor superheat.

Unfortunately some combination of system problemas can give similar symptoms or even disguise these, example you may get normal condensing pressure if you also have hot air recirculation.

[Brian_UK]

Don't know if this helps but it is a manual for a Marstair MCU condensing unit which is basically an IMI double.

http://www.heronhill.co.uk/productde...cfm?prodID=MCU

[hammy]

thanks for your assistance its now running like a dream