Input needed.

An area where professionals can discuss HVAC /R related issues and topics.

- Input needed.

Postby nomadpeo » Wed Jan 12, 2011 10:53 pm

i'm late viewing this question and perhaps you have already got your answer. i will throw in some info just the same. if you have removed the 410-a, replaced the filter drier and pulled a deep vacuum, you should be able to recover from the error made by others. as far as the performance, you can test the pumping capability of the compressor if you have a liquid line service valve. pump the unit down with the r22 charge in it. if the concenser has capacity to hold the charge and you can pull it down to 0 psig, open the liquid line service valve again and test the compressor current. make sure it is less than the RLA on the name plate. once you successfully run those tests, you should be able to verify refrigeration functionality and performance by setting the charge by superheat. the refrigerant charge in a system utilizing a fixed metering device can only be set by superheat. superheat is defined as 'heat added to a gas'. the superheat in this case is the amount of heat added to the refrigerant after all the liquid refrigerant has boiled. verifying superheat confirms that - (a) all the refrigerant did indeed boil and that (b) all the refrigerant boiled as the air containing the heat load passed over it. this state of liquid and gas mixture in the evaporator is referred to as 'saturation' and can only be regulated by ensuring the correct level of refrigerant is in the system. generally, if superheat (difference between suction pressure converted to temperature and the suction line temperature) is within a range of 7 to 20 degrees farenheit, the system should be operationg fairly efficiently. the other two contributors to this exchange are digging for this information. the other factor involved in performance is humidity control. if the evaporator is within an acceptable temperature range (40 to 45), the relative difference between the temperature of the entering air (return air from the house) and the evaporator surface will cause the humidity contained in the air to condense to liquid (water) and drain away, thereby lowering the relative humidity. an often ignored fact is that a fixed type metering device depends upon liquid pressure entering the orifice to determine ultimately the quantity of refrigerant entering the evaporator. therefore, the cooler the outdoor ambient, the higher the superheat (lower temp, lower pressure, less volume). keep in mind that if a manufacturer has a chart or charging instructions for a matched set of equipment (c.u., coil and m.d.), that information overrides any generic method of charging.

having said all that, let me address your performance data. a common error in the field is to judge by pressure readings. set the freon level by superheat for fixed md, seet freon level by sub-cooling for txv, clean coils and verify matched components and ducts. if those things are addressed and your compressor is pumping, there is no reason for poor performance. your low delta-t is possibly due to low freon. those pressure readings relative to each other are not necessarily out of acceptable range, but pressures, though useful for a snapshot indicator of some things, cannot be used to determine freon level. my suspicion is that you are running high superheat and therefore a starved evaporator. the powerful part of the energy exchange in this system is the latent heat transfer that takes place when liquid boils in the evaporator. too much or too little will minimize performance. as far as the ill effects of the system having run with the wrong refrigerant, it is not likely that is the source of your problem. the key balance that results in an acceptable delta-t (diffeence between the return air and supply air temps, ideally 18) is a properly saturated evaporator. this condition depends heavily upon a properly sub-cooled liquid. to reiterate, your focus should be the following - no non-condensibles (water, air), correct superheat, clean coils, proper match.
Most Valued Contributor
Posts: 278
Joined: Wed Jan 12, 2011 10:10 pm

Return to Technicians Only