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A/C advice, tech was less than helpful

Posted by dishiki (My Page) on
Thu, Jun 9, 11 at 18:24

We had a tech come out for the annual maintenance. Our numbers for the upstairs unit were skewed.

Here is the rundown. The Condenser is a 15 year old Rheem. It was manufactured on 4/96 and it is 2.5 ton. The model number is RAMA-030JAZ. The furnace is 6 years old. It is a Rheem Super Quiet 80. It was manufactured on 10/05 and the model number is RGDN-05EAUER.


The tech said that the furnace was 2 ton, and that it was choking the system. The system has been cycling alot at night and it has been taking a longer time for it to cool. Last year it would take 2-3 hours to go from 78 to 73 degrees. This year it is taking about 7 hours, and at night it is kicking on and off often.

Here are the numbers that the tech gave:

Outdoor temp 89
Indoor temp 76
suction pressure 60.3
discharge pressure 305
superheat 24
subcooling 43.1
supply air temp N/A
return air temp N/A
voltage 244.6
system amps 12.6
compressor amps 10.9
motor amps 1.6
wiring ok
contactor volt drop .3
outdoor coil dirty
evaporator coil can not see
drain lines cleared yes
refigeration leaks none
condensate pump none

In his notes he mentions system is running very high head pressure and low suction. He also has a different number for subcooling in his notes, 38.9.

I did my due diligence and looked at the system myself. The furnace is actually a 3 ton system, so he was wrong on that account. The previous owner had the downstairs unit moved upstairs back in 05 and in the process put in a new coil and furnace. This is the workorder info from the install back in 05:

1 Rheem 50,000 BTU 80% efficient furnace with 3 ton Drive
1 Relocate A/C from downstairs to upstairs
1 3 ton 12 seer coil 17" installed

The tech said my system was mismatched because he thought it was a 2 ton furnace and that it needed to be replaced. Obviously, I do not have faith in his assessment. Does anyone have any idea what the issue could be, and why my subcooling and super heat, and pressure numbers are so skewed, and what I can do to make the system run more efficiently?

Thanks


Follow-Up Postings:

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RE: A/C advice, tech was less than helpful

While waiting for a pro to answer, you may want to consider that you may have a partial blockage in the line somewhere between the compressor and the evaporator (in the liquid path).

"If Superheat is very high and Sub-Cooling is a little high:
Could have blockage in coil, TXV strainer screen - settings, etc., orifice, filter dryers etc."

Do you know whether you have a TXV?

Here is a link that might be useful: He DOES ramble on


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RE: A/C advice, tech was less than helpful

Your subcooling is way too high on that system. Either you have a restriction at the metering device and only if it's a txv since your superheat is ok, or you are way overcharged. Wash the condenser coil and check again. If necessary recover refrigerant until you have around 9 deg subcooling. It is actually worse to be overcharged than to be undercharged as far as system capacity goes.


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RE: A/C advice, tech was less than helpful

sounds like your issue is on the refrigerant side rather than air handler side. The furnace is 50,000 btu's which is considered equivalent to 2 tons I'm not sure what is meant by 3 ton drive although I would think 1200 cfm.


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RE: A/C advice, tech was less than helpful

Terminology: Ton usually refers to A/C output(12000 BTU/ton). In reference to furnace, it is shorthand for fan speed based on 400CFM/ton. Since different size A/C units can be matched with difference size furnaces(depending on location and house characteristics), Furnaces are sold with two size parameters: heat output(BTU) and air fan speed. The latter must match the A/C unit(heating is much less sensitive to ducts). Fan speeds are adjustable within a range by dip switches on the main circuit board.

Finally, furnace fan speed should be appropriate for the size of the main duct the air is blowing thru. Too small ducts cause a variety of problems including uneven air temperature, excessive temperature fluctuations in rooms closest to HVAC unit, excessive wind noise and coil freezeup.


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