Miss match

[william_wye]

I have a slightly oversized condensor with a smaller evaporater . Whats happening is, the evaporator clogs with ice before room temp is achivied. I have tried controlling this with LP control but the unit short cycles. Is there any other way of solving this without changing either condensor or evaporater.

[chillin out]

Fit a fan speed controller to the condensor.


Chillin

[Peter_1]

Having a too large condensor isn't the source of your problems.
Is the unit not undersized (seems it is), is there some way to defrost the system, where starts the frost, what's the rooms size, compressor size, evaporating temperature,...

Too many unanswered questions too help you now.

Fitting 2 thermostats the old fashion way like we described in a thread of some weeks ago could solve your problem.

[afeef]

hi
the frost in evaporaror is due to low speed air flow thru it ,,,and this is cased by dirty sponge filter or the same evaporator having dirties in it
another reason is : the weather out side room is cold,this is happen befor sunrise time

or the last reason is : lost of part of refrigerant gas in the a/c
check every reason above,,,and inform us the remedy you do
best regards
afeef

[Toosh]

Hi Afeef If you see the location he is in Fiji It don`t get cold outside there

[william_wye]

There is a defrot timer with 6 defrost intervals at 30 mins each. The evaporater was designed for that room size . The condensing unit was insalled by someone and apparantly he installed a slightly oversized one.

[william_wye]

The evaporater has no accumulation of dirt that is not the cause of the frost. What happens is the coil ices up before the desired room temp is achivied

[chillin out]

The coil is icing up because the evaporating temp is too cold.

If what you say is correct and the condensor is too big, then you may be over-condensing and this will be the cause of the ice up.

Fit either a fan speed controller or a high pressure switch to control the fan.


Chillin

[Servicefrigo]

1.change the unit cooler ( recomanded )
2.Change the fans from unit coolers with otters a litle little bit bigher (not recomanded )
3. Control the condensing pressure ( recomanded )
Regards

[afeef]

hi dear
now what remaining reason for the frost is lake of refrigerant
for how many days this condition is happend to you ?
if it is less than a month ,,,i think that the R 22 biggining to escape
after 1 month all the R 22 will be over and you will need to find the leak and charged again
please replay me
good day
afeef

[william_wye]

Thanx chilling-out. Did what what you said. Fit a high pressure swicth .Fan cut out at 250 psi cut inat 380psi. The frost is gone and room temp is maintained at -20*c to -12*c. Do you think I have the right pressures
Thanx again

[Rob S]

With out having any idea as to what refrigerant you are running. Usually set my Cond Fan Cycling controls at around 220 CI and 180 CO. This works for R22, 404a, 507, or the like.

[william_wye]

It is a 404a application. I have reduced the CO to 200 and the CI remains. Here in Fiji we have an average ambient of 32*C.

Regards

[chillin out]

Glad I helped,

Fan cut out at 250 psi cut inat 380psi.

I think I would try and get a closer diff than that.

You could try in at 300 psi

Out at 250 psi

380 psi seems a bit high.

Chillin

[william_wye]

Cheers mate

[renzo]

this happens a lot of times when the TXV is faulty or bulb is in wrong location.

[slingblade]

I don't think that air flow through the condenser tends to be reduced by fan speed controller

well ive got news for you, it does. as the discharge pressure/temperature rises the fan speeds up increasing the airflow and then as the pressure/temp. falls the fan will slow down reducing the airflow, obviously.

a lot of units designed for use out outside will have fan speed control or low ambient kits to reduce excessive subcooling of liquid supplied to the expansion device in cold conditions where the condensor could be said to be "oversized" which i believe was the original problem. this in turn will help to raise suction pressure and lower superheat, in order to help with the frosting problem.

Reducing the air flow will warm up the liquid line exesively

the only reason for this i can see is if the condensor is undersized or fouled, given the speed control is set correctly.

regards

slingblade

[Peter_1]

...
a lot of units designed for use out outside will have fan speed control or low ambient kits to reduce excessive subcooling of liquid supplied to the expansion device in cold conditions .....

What is 'excessive subcooling' and can it harm the function of a TEV anyway??
What will the TEV do if liquid is subcooled much more then normal conditions?
Overfeed or underfeed?
And will this cause frost on the evaporator?

[slingblade]

What is 'excessive subcooling'

excessive subcooling or overcondensing as its often called is where the liquid exiting the condensor is not only saturated and subcooled to plant design spec. but cooled further still. the use of fan speed controls will hold the discharge and liquid temps the same regardless of the ambient temp.

and can it harm the function of a TEV anyway??

no. the txv is a superheat control device and will not be harmed at all by low inlet liquid temp.

Overfeed or underfeed?

i suspect it will underfeed as the amount of heat required to boil the subcooled liquid will be greater than non subcooled. in effect with the same evaporator load and over subcooled liquid the evap temp will fall and the valve will throttle back.

And will this cause frost on the evaporator

Yes, it will. as clearly stated in the first post. since the fitting of a fan speed control the problem has gone!!!

Thanx chilling-out. Did what what you said. Fit a high pressure swicth .Fan cut out at 250 psi cut inat 380psi. The frost is gone and room temp is maintained at -20*c to -12*c. Do you think I have the right pressures
Thanx again

See what i mean?

[Peter_1]

excessive subcooling or overcondensing as its often called is where the liquid exiting the condensor is not only saturated and subcooled to plant design spec. but cooled further still. the use of fan speed controls will hold the discharge and liquid temps the same regardless of the ambient temp.

no. the txv is a superheat control device and will not be harmed at all by low inlet liquid temp.

i suspect it will underfeed as the amount of heat required to boil the subcooled liquid will be greater than non subcooled. in effect with the same evaporator load and over subcooled liquid the evap temp will fall and the valve will throttle back.

Yes, it will. as clearly stated in the first post. since the fitting of a fan speed control the problem has gone!!!

Fan speed control will only maintain a stable pressure, but not the discharge temeprature nor the liquid temperature. You can maintain a stable HP and still subcool very deep without problems.
The more you subcool, the better for the system.

Excessive subcool will make that the TEV will overfeed, not underfeed.
So if you have very high subcool, a smaller orifice must be installed.

I haven't read this in the first post. Probably the liquid lines causes a too high pressure drop.
I still disagree that a decrease of the subcooling has solved the problem. Increasing the HP has probably solved it.

William_wye, what is the cooling capacity (or type and brand) of the condensing unit, capacity of the evaporator (or type and brand), the liquid line diameter, the length of it and what TEV was used?

[slingblade]

then we shall have to agree to disagree. there is only one man who can settle this and he has gone surfing in the snow this weekend, the moron.

[thebigcheese]

not really a proper way to find out about condenser size, but u could try blocking part of it off so only half or 3quaters of it can actuly reject heat.

[sagittarius]

There is a defrot timer with 6 defrost intervals at 30 mins each. The evaporater was designed for that room size . The condensing unit was insalled by someone and apparantly he installed a slightly oversized one.

I have a fundamental question:What affects the refrigeration system due to oversized condensing unit?and the relationship of condensing unit and evaporator?
TKS!

[frank]

A fundamental answer then sagittarius.

A refrigeration system is in balance when the heat absorbed at the evaporator, together with the heat of compression, is rejected at the condenser.

If any one or more of these components is under/oversized then the system becomes out of balance.

If the evaporator is oversized then more refrigerant will be needed to fill the coil and excessive heat will be absorbed which cannot be rejected efficiently. Likewise so with all other components.

Too large a compressor etc. etc.

[NoNickName]

Fan speed control will only maintain a stable pressure, but not the discharge temeprature nor the liquid temperature. You can maintain a stable HP and still subcool very deep without problems.
The more you subcool, the better for the system.

Excessive subcool will make that the TEV will overfeed, not underfeed.
So if you have very high subcool, a smaller orifice must be installed.

I haven't read this in the first post. Probably the liquid lines causes a too high pressure drop.
I still disagree that a decrease of the subcooling has solved the problem. Increasing the HP has probably solved it.

William_wye, what is the cooling capacity (or type and brand) of the condensing unit, capacity of the evaporator (or type and brand), the liquid line diameter, the length of it and what TEV was used?

A full post of good practice and deep knowledge.
Yes, fan speed regulator only control pressure, not subcooling, which will increase as the ambient air cools.
The more the subcooling, the lower the evaporating temperature, all the rest unchanging.
This side subcooling effect also happens on water cooled systems when pressostatic valve are installed: lower water flow, but the same entering water temperature, with subsequently higher subcooling.

The refrigerant charge is highly dependent on design conditions. If conditions change, it should be noted that the refrigerant charge will just be a compromise.

[US Iceman]

I have a fundamental question: What affects the refrigeration system due to over sized condensing unit?and the relationship of condensing unit and evaporator?

Since you have specified the use of a condensing unit as the basis of your question any cooling capacity increase or decrease of the condensing unit will unbalance the system.

If the condensing unit capacity is too high, the suction pressure will be lower than necessary. Conversely, if the condensing unit capacity is too low, the suction pressure will be higher and loss of temperature control in the space will result.

If the condenser capacity itself were slightly greater the discharge pressure would decrease. A good thing to have.