Our install department installed a brand new single stage 2 ton Carrier air conditioning unit and I was sent to do the startup. The initial indoor air temp was 69 so I ran the customer's furnace in order to bring the indoor air up to 75 degrees, the outdoor air was already at around 75 degrees. The Amana Distinctions furnace's blower fan was set on high for cooling and there was a clean air filter in the filter cabinet. After starting up the AC system and letting it run for 20 minutes the subcooling was 3.5 degrees Fahrenheit and the superheat was around 0.6 degrees Fahrenheit. Now from what I know a low subcooling means that it is low on charge but having almost no superheat means that the evaporator is flooded which normally indicates an overcharge. The installers did not add any charge, the only refrigerant in the system is what was factory charged and the line set length was roughly 25 to 30 feet. I spoke with another technician and he told me not to worry about the superheat but to focus on the subcooling and so I added a total of 1 lb 13 oz of r410a in order to bring the subcooling up to 12 degrees Fahrenheit, the data plate says 11 degrees Fahrenheit of subcooling and I was initially around 10 until I emptied what was left in my hose. The superheat was still almost nothing and I moved my pipe clamp sensor from the bottom of the suction line to the top of the suction line at the outdoor suction valve and I had a 4 degree superheat at that point. it still seems as if the evaporator is flooded, does anyone have any insight? It is just curious to me that there was almost no superheat to begin with and the subcool was low.
After starting up the AC system and letting it run for 20 minutes the subcooling was 3.5 degrees Fahrenheit and the superheat was around 0.6 degrees Fahrenheit. Now from what I know a low subcooling means that it is low on charge but having almost no superheat means that the evaporator is flooded which normally indicates an overcharge...I spoke with another technician and he told me not to worry about the superheat but to focus on the subcooling, so I added a total of 1 lb 13 oz of r410a in order to bring the subcooling up to 12 degrees Fahrenheit, the data plate says 11 degrees Fahrenheit of subcooling and I was initially around 10 until I emptied what was left in my hose. The superheat was still almost nothing...does anyone have any insight?
The evaporator is flooded and the other technician gave you bad advice.
But since the other guy said charge to subcooling, we'll assume the evaporator has a TXV, in which case the initial low superheat and subcooling numbers indicate the valve is overfeeding...grossly.
I would first make sure of what type of metering device you have. If it's a piston make sure it's there and that it's the proper size.
If it's a txv check bulb etc.
You may want to pull the charge and weight it in .
Just a couple thoughts. Sounds like light load most likely. I would go back when it is hotter outside and recheck your numbers. I would also pull the evaporator panel and make sure the coil is clean and unobstructed.
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That doesn't seem right, does it? <g>
Is the piston the correct piston size for the condensing unit?
Is the TXV bulb firmly attached to the suction line?
A low suction superheat does not 'indicate' an overcharge. Low suction superheat is the result of too much refrigerant in the evaporator for the heating loading of the evaporator at that moment in time.
Post the startup report data:
Outdoor Ambient temperature
Condenser air temp in
Condenser air temp out
Head pressure
Suction poressure
Liquid line temperature
Suction line temperature
Air temp entering evaporator
Air temp leaving evaporator
PHM
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Originally Posted by jperigo
Our install department installed a brand new single stage 2 ton Carrier air conditioning unit and I was sent to do the startup. The initial indoor air temp was 69 so I ran the customer's furnace in order to bring the indoor air up to 75 degrees, the outdoor air was already at around 75 degrees. The Amana Distinctions furnace's blower fan was set on high for cooling and there was a clean air filter in the filter cabinet. After starting up the AC system and letting it run for 20 minutes the subcooling was 3.5 degrees Fahrenheit and the superheat was around 0.6 degrees Fahrenheit. Now from what I know a low subcooling means that it is low on charge but having almost no superheat means that the evaporator is flooded which normally indicates an overcharge. The installers did not add any charge, the only refrigerant in the system is what was factory charged and the line set length was roughly 25 to 30 feet. I spoke with another technician and he told me not to worry about the superheat but to focus on the subcooling and so I added a total of 1 lb 13 oz of r410a in order to bring the subcooling up to 12 degrees Fahrenheit, the data plate says 11 degrees Fahrenheit of subcooling and I was initially around 10 until I emptied what was left in my hose. The superheat was still almost nothing and I moved my pipe clamp sensor from the bottom of the suction line to the top of the suction line at the outdoor suction valve and I had a 4 degree superheat at that point. it still seems as if the evaporator is flooded, does anyone have any insight? It is just curious to me that there was almost no superheat to begin with and the subcool was low.
PHM
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When faced with the choice between changing one's mind, and proving that there is no need to do so, most tend to get busy on the proof.
Yeah, sounds like a overfeed. But, you haven't told us if your suction pressure is slightly higher than normal or lower. Also, discharge temp can tell you if your unit will survive. Here's one the other day I found on a PM. Been running like this for 7 yrs. I think the suction accumulator allowed it.
There is a TXV at the indoor evaporator coil and I checked and the bulb is insulated and on the suction line
I've started up quite a few new systems that overfed...they were non-adjustable valves so no options. But all those I remember fixed themselves after a day or two's operation.
I don't know enough about valve design or construction to say what would cause the malfunction. You might try chilling the bulb in ice water with the system off. The higher off-cycle evaporator pressure and low bulb pressure would both have a closing effect on the valve which might "unstick" it.
Registers all open? Blower run cap is good? Blower wheel clean? I think you did your best given the circumstances by heating up the house but that won’t really replicate an actual heatload. By the time system has stabilized the temp has probably dropped lower than what you started with. Get your pressures, sat. temps and deltaT and get back to us
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Originally Posted by jperigo
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