Header assembly or Evaporator coil?

palatero

I've been working on a carrier rooftop unit. The evaporator coil keeps freezing up, not the whole coil, just the bottom portion or about the lower fifth all the way across left to right.

The unit has good airflow, a new blower wheel belt, properly sized duct work, clean evap coil. So I am thinking there must be a restriction in that portion or circuit of the coil or the header assembly going into the coil.

My questions are does this sound like the right diagnosis?
Is there anything else that could be causing this?
Would it be better install a new header assembly or the whole evap coil?
I called carrier and they said when you buy the coil it comes with the header assembly attached, or I can buy the header assembly seperate.

The unit is a model number 48TFE007---511 and was manufactured in 2005.

Thanks for reading,

palatero

user865

You should never repair a coil, only replace it. What are your pressure readings? An undercharged system can result in the problem you're describing.

nicktech

possibly an under charge or a bad TXV, check your super heat. is there a shortage of refrig starving the coil? is the TXV starving the coil? if there enough liquid entering the TXV? Is the condenser condensing all the vapor into a liquid, check subcooling. is the compressor delivering the right amount of refrig to the condenser in the first place. is the condenser clean, is the condenser fan motor running at the right speed? there are alot of possibilities that would cause that symptom.

beenthere

So what did you find was the problem.

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hvaclover

he got his answer on Hvac-Talk.

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palatero

Thanks for the replys on this one. The pressures on this were normal, but high side was slightly high and low side slightly low. There is no TXV on this evaporator. Condenser coil was good but I cleaned them with a good foaming cleaner anyway.
Then I changed the evap coil which includes a new header, instead of just changing the header assembly only.
The system runs very good now, superheat is good, subcooling good, temp split is normal.

Thanks again for the help

wrightchoice

Those coils have a fixed piston at the exit of the header assymbly and the enterance to the coil. Had the same problem and cut the old coil apart to see exactly what was causing the restriction, found some of the orifixes clogged.

artco

Along with what everyone else says check the return air grilles, are they plugged with dust and dirt? Are all the supply registers open?
Has someone changed evap fan speed?
Are the dampers for the economizer operating OK?
Is the thermostat setting to low?