Return air too cold?
I just replaced my home A/C system with Carrier Infinity 5-stage 24VNA960. In the few weeks since installation, we’ve had problems with freezing evaporator coil. Below are some details:
* Thermostat on 1st floor, which we keep set to around 67 degrees. This typically results in the basement being about 60 degrees, and the 2nd floor is about 72 or so.
* Techs have been to the house several times. The story so far is that the equipment is working as intended and the air coming into the blower is drawing in cold air from the leaky return system in the basement which is causing the freezing.
* Our prior system (I don’t recall the model, but it was a 2-stage Carrier) did not have any problems with freezing at the same thermostat set point.
* Their answer was that the original system had a piston valve, and this new system has a TXV.
* We’re still in discussion and diagnosis, but it seems the recommendation so far is to have the basement registers sealed and insulated. (supply registers in the basement are closed).
* The house was built in 1995 and we are original owners. Basement is unfinished) The A/C system we just replaced was installed in 2009.My questions:
* I don’t understand how the TXV would be more likely to cause freezing due to colder return air. If anything, shouldn’t it be MORE capable than the piston at controlling the refrigerant flow to prevent freezing?
* Has anybody encountered a similar situation that has been resolved by sealing and insulating the ducts?
* Which leads to my next question, which is, if you have had success in sealing the ducts, any recommendations on the manual mastic-based approach versus the Aeroseal approach?Thanks in advance for your insight!
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Was the system properly sized with a load calculation? Was the static pressure tested and airflow determined? Just curious, I am betting oversized equipment on undersized duct system. I only see this on 80% of calls.
IDK, freezing coil on a 5 stage unit sounds like a defect to me…
Originally Posted by ksefan
Was the system properly sized with a load calculation? Was the static pressure tested and airflow determined? Just curious, I am betting oversized equipment on undersized duct system. I only see this on 80% of calls.
The new system is the same size as the system it replaced, which was working fine for 13+ years until it developed a leak in the coil.
IDK, freezing coil on a 5 stage unit sounds like a defect to me…
A defect where? Compressor? Coil? TXV? Something else?
Ice means the system is removing more heat than the system has airflow to remove.
So, either its a low charge, or a low airflow situation below the low stage capability, or the system is locked into a higher stage of cooling than the blower is set to flow.
It could also be a defective txv, but many measurements are needed to determine this.