Air Conditioning System Excessive Airflow with Excessive Charge
Excessive Airflow coupled with an Excessive Charge = an A/C Operating 50% below its Btuh Rating! 
A 3.5-Ton Matched System Delivering 1.25-Ton of Heat Transfer! - with Darrell Udelhoven

HVAC Efficiency Overview My Audio overview; listen while doing other things 
Research Performance Assessments | CONDENSER TEMP-SPLIT | Basic AC Overview - Specs VS. Reality
Hot ATTIC or Garage Air Entering Return Air  |
Gurgling Pulsating Sounds at TXV
Air Conditioning Rip-Off Scams | An Important Efficiency Instructional Video - 4 All Home Owners Too - Last Half Best

Low evaporator airflow is the common problem in older systems; a HOT conditioned space coupled with EXCESSIVE AIRFLOW resulting in Overcharging could be a problem in newer air handler models! This is merely an illustration of a few useful diagnostic procedures to reveal this problem. This is an example of a 3.5-Ton matched AC system delivering only 1.25-Ton of heat transfer! Wow, huh? Yet pressure appear normal, however due to a very low heat-load, AMP Draw is not high but is quite low.

Extreme over charging can happen when the conditioned space is extremely hot along with an excessively high airflow setting and "the tech 'try's' to charge for a beer-can cold suction-line.  Also, when it is too cool outside (below 70ºF) with a light load on the evaporator, the tech may try to get the pressure up by adding refrigerant, resulting in an overcharged system during normal operating temperatures.

Since the condenser is so easy to check for proper operation, and it is matched to the compressor, "it gives a good indication of the amount of both sensible & latent heat being removed from the cooled space," in my experience using other cross-reference data with it, check both superheat & sub-cooing, it is far more reliable than merely checking amp-draw to ratings.

First, we must determine there is plenty of airflow to adequately heat load the evaporator coil. Then, after verifying that the condenser is clean and the CFM airflow through a clean evaporator appears correct, "the condenser air temp split will reveal if the evaporator is being fully heat loaded." In addition, check for a slow running condenser fan (a suspect if the motor runs too hot) or an incorrect fan blade or blade position (change to unit specs).

Checking the condenser and its fan blade positioning & proper functioning first, is alway essential to the proper order of the trouble shooting sequence; it is only the following of the proper sequence that the problem(s) will be revealed to be resolved. FIRST & foremost the indoor airflow through the evaporator coil MUST be checked & be made correct before any checking of the refrigerant charge. Of course, the duct system must be properly sealed & blower wheel blades & indoor coil need to be clean.

a.) An adequate outdoor condenser air temperature split (ºF Temp rise) would indicate that the evaporator is properly supplying heat to the vaporizing refrigerant; -- therefore, "in this case," the refrigerant device is controlling at the wrong superheat, caused by either, an overcharge, incorrect orifice, or a wrong temperature setting or malfunctioning TXV.  On table-top condensers, Techs can also use the high-side gauge's, Saturated Condensing Temperature reading - minus the outdoor ambient air temperature, or condenser entering air to arrive at the split.

b.) With a cap tube or piston flow-rater, little heat being removed by the condenser says that the evaporator can't heat-load the system -- the airflow or heat-load through it could be too low, or due to combined factors, the evaporator is so flooded with liquid it really isn't evaporating.  A TXV will merely regulate the flow rate to meet its superheat setting. A low heat-load through the evaporator coil in a grossly overcharged TXV system results in refrigerant back up in condenser coil, greatly reducing the condensing capacity of the system on rather warm days.

On fixed metering devices, the easy check is to remove refrigerant until the suction superheat comes up, then recheck the temperatures and pressures, which should make for an easy diagnosis.

If the compressor being inefficient was the cause for little heat being removed, and the evaporator loading, refrigerant charge and orifice were correct, the suction pressure would be unusually high and the discharge pressure would be unusually low, "not the problem here."

The pressures will indicate whether the compressor is okay, --it is possible that the system is imbalanced possibly due to, low evaporator heat loading, charge level, and/or wrong orifice size. (While not a factor here, an oil-clogged system would be another factor to consider in inadequate evaporator loading providing similar conditions are found on a system.) 

c.) Higher than expected heat removal by the condenser is an evaporator too loaded up -- not a factor in this troubleshooting illustration. I'm including it to complete the possibilities for AC systems in general.

Regarding the amp draw -- assuming all the figures are correct -- the compressor and condenser are under-loaded, the air temperature rise across the condenser is low (could be low evaporator airflow, dirty filter, dirty blower wheel and evaporator coil. The evaporator inspected okay, the return air ducting and the supply air ducting at the unit is okay, leaving mismatched components or too much airflow and/or a grossly overcharged system.) 

D.) It is critical not to overcharge (or undercharge) a fixed orifice evaporator coil. 

It will lessen capacity on the system because to remove heat, the liquid refrigerant must absorb enough heat in a timely manner to boil, or become a heat-loaded saturated vapor. If the system is overcharged, the evaporator becomes flooded due to a too fast “Mass Flow Rate of Refrigerant” and the boiling change of state (absorption of heat) does not happen in a timely manner to utilize the correct amount of coils and fins before leaving the evaporator. Instead of becoming saturated and flashing off early in the evaporator before it comes close to completing its cycle through the evaporator, it saturates near the exit and on into the suction line and back to the compressor.

It is critically important to properly charge a Fixed Orifice evaporator Metering Device or the efficiency and BTUH of the unit will tank! Since you are talking about a fixed orifice system which mimics a capillary tube system, from my ARI text book, p- 107, Air conditioning system; 90°F ambient indoors 75-db 63-WB - 50%-RH. Refrigerant charge 100% net capacity of unit 26,400-Btu/hr; charge increase 5% or (3 oz) capacity dropped to 24,600; another 5% increase (3 oz) in charge capacity dropped to 19,000-Btu/hr. A total overcharge of 15% or (9 oz) reduced the capacity to only 13,000-Btu/h, less than half capacity. That would put a correct charge at 60-ounces, or 3.75 lbs. Source of this paragraph: The Air Conditioning and Refrigeration Institute (ARI) (textbook, p- 107).

Overcharging a system affects the “Mass Flow Rate of Refrigerant.” Proper mass flow rate of (liquid) refrigerant through an evaporator is as important as proper superheat and subcooling; as both are affected by the mass flow rate.

In the past, most residential systems had Fixed Orifice refrigerant metering devices therefore getting the mass flow rate within the proper design perimeters is critical; overcharging these systems will skew the Mass Flow Rate too much and reduce capacity and efficiency. (TXV's are NOT as critical.)

It is also a good idea to check if the piston/orifice is correctly sized according to the manufacturer's literature. Charts for orifice size are only useful when you have the outdoor and indoor unit model numbers. When trouble shooting a system, I found a piston orifice installed backward at an apartment complex; the unit performed as if the compressor had bad valves.

It is possible to find three or more things wrong on one system, which is what separates the real Techs from the dudes.

"In this actual case example, the initial causative factor was excessive air flow possibly coupled with a very hot conditioned space -- cranked-up the CFM airflow too much, then also with a hot conditioned space, added too much refrigerant trying to get a beer-can cold suction line, and never using superheat charging." When the conditioned space cooled to a normal 72 to 74 degrees and the return air filter became loaded, liquid refrigerant would flood the evaporator coil. An under-heat-loaded - flooded evaporator coil won't evaporate the liquid refrigerant, which is what absorbs heat, therefore the condenser will be under-loaded, and thus the low amp-draw.

The air temperature off the condenser or the high side Saturated Condensing Temperature gauge reading - minus the outdoor ambient temperature yielded only a 13.89 Temp Rise.
All the indicators point to an overcharged system.

Checking the condenser discharge air temperature split is an effective performance test measure that should be part of any maintenance check which even the owner can perform. Since there are no duct variables to contend with, the condenser is easy to inspect, thermometer calibration isn't an issue using the same thermometer for both condenser in and out air, wet bulb temperature doesn't matter, and the compressor is closely matched to the condenser.

Check Return Air (RA) at grille & at entry of blower for heat gain, due to hot source Return Air leaks.

Where air-handlers' set over Return Air Chambers, check for air leaks through the sheet- rock & down the wall studs from  the attic - this is a fairly common condition that will overload the air conditioning system.


P.S.; Another Chapter…



*Basics Featuring the Testo 556 >Video of a very thorough Air Conditioning Testing setup

The Testo 416 Airflow Test Checking airflow must be performed before charging a system. More HVAC Videos on other pages!

The North Country Oil furnace A/C or heat pump scenario; Low airlow is the usual major problem:

Any good Tech should already know what I am going to illustrate here; this is for Homeowners & any who can use the least costly way to deal with this too common a problem in the cold North Country. 

We are moving into the cooling season; however, any changes in equipment should consider how every component matches with optimal airflow efficiencies.

My lowest cost solution to the cold climate oversized Oil furnace with a small tonnage A/C evaporator coil which requires nearly half the airflow as heating:

I ran a check on my late brother’s home & the summer cooling heatload is about 14,000-BTUH. 

The original scenario, had much less airflow than required for 1.5-Ton cooling; its 2-Ton A-Coil wouldn’t flow 1150-cfm for heating

I did a lot of other figuring; 45,000-BTUH Output should heat that small single story home. 

However, with the 140,000-BTUH input, 112,000 output Oil furnace installed; the nozzle size can be dropped from one gal an hour (we’ll use 139,000-BTUH input) to .75 @100-psi, the BTUH drops to 103,500 input, this furnace tested at .74% efficiency; *103,000 = 76,590-BTUH.

Using a 90F heating temperature rise, which Thermo Pride can stand; (90*1.06 here) 76,590 / 95.4F is 803-cfm.

Therefore, the 2-Ton A-Coil will handle the CFM; mounted +6 inches above the furnace, it has the flow capacity to work okay in both heating & cooling modes.

With a third HP belt-drive motor, you could simply adjust the RPM down by turning the adjustable motor pulley out enough to get to 700 or 600-CFM for the 1.5-Ton A/C.

The other solution is to install a multiple speed direct drive motor with the fan relay energizing the cooling speed tap. 

This rather common situation in cold climates seems not to be properly addressed my Techs, & the HO does not know why things don't work well.

We should all work to improve efficient use of high cost energy ... so America & everyone wins. More proofs in below Article to get  airflow right.

Why HVAC Systems are Less Efficient than You May Think

We pulled test data from over 20 systems from our CommonCents™ database. This is an online testing and diagnostic software that NCI members use to collect and analyze information and present their findings to their customers. These were systems that had complied with his program’s energy standards and all had received substantial incentive payments. Here’s what we found:

• The average operating efficiency was 63% of equipment rated capacity at the time of the test.

• The average total external static pressure was operating at .86-in. of pressure with an average maximum fan rated pressure of .57-in.

• The system delivered airflow at the supply registers averaged 261 CFM per ton at registers (400-cfm per/ton is normal airflow).


Gurgling Pulsating Sounds at TXV: Low evaporator heat-loads lead to reduced liquid line mass and increased evaporator mass could be due to airflow problems. Eliminate low evaporator heat-loads before looking into adjusting the refrigerant charge.  Gurgling and pulsation noises at the expansion device can be caused by low evaporator circuit heat-loads, low charge, and/or non-condensibles and moisture in the system. Unbalanced airflow through the various distributor circuits of the evaporator coil will cause the TEV to close down refrigerant flow starving the coil. Piston-flow-rators will make it impossible to properly charge the system and cooling will be greatly compromised unless you eliminate the cause! "Put your ear on the liquid line at the evaporator coil."

On every Rheem condenser cover it lists "non-condensibles and or moisture" as causes for a gurgling or pulsating noise at the expansion device. The entire evaporator circuits, may not become active for various reasons, - "the entire coil must become fully active for efficient performance."
The purpose of these recommendations is to provide liquid refrigerant at the expansion device and provide efficient operation. Hopefully, this will aid your research.  If I can be of additional assistance, contact me.

I estimate over 90% do not properly purge & evacuate contaminated central air conditioning systems.

The Triple Evacuation Method is normally done on the new R-410A Split Central air conditioning systems:

First, remove any valve cores with a special  valve core remover this will speed up the evacuation time. Back service valves two turns off their back seat.

1) Re-claim unit charge (Recover all the refrigerant)

2) Charge system to 150 PSIG with dry nitrogen and leak test

3) On contaminated systems replace the filter dryers. Then Repair all leak(s)

4) Evacuate system to 500 microns valve off & see if it holds 500 microns for ten minutes, if it holds, break the vacuum with dry nitrogen

5) Evacuate system to a deeper 300 microns, valve off vac pump, & again break the vacuum with dry nitrogen

6) Evacuate system to 300 microns and charge unit (Recharge with fresh clean refrigerant)

7) Check to see if the Supply and Return air ducts were correctly sized & sealed by the original installer.

The “micron” is a metric unit of measure for distance. The micron is a unit of linear measure; one micron equals 1/25,400ths of an inch. Modern high capacity vacuum pumps help speed up the evacuation process.

This is merely an illustration of some useful diagnostic procedures.
One Research Performance Assessment revealed:
Several recurring factors that accounted for inadequate flows:

* Return ducts and return grills were often undersized
    * Blower Fan set to wrong speed for cooling operation
    * Filters blower wheel blades and cooling coils were dirty
    * Duct system static pressures were elevated due to circuitous runs, pinched ducts etc.
    * Larger outdoor units were installed without changing the indoor unit and duct system
    * Devices had been added which increased system static pressures.


Take the condenser entering air temp and leaving air temp, subtract for the temp-split. As a double verification: You can use the high-side (SCT) Saturated Condensing Temperature minus the outdoors-ambient temperature; the difference gives you the condenser temperature-rise or temperature/split. There is NO excuse for not utilizing this important diagnostic check. Always use an accurate volt meter and amprobe to make sure you are not overloading the compressor's Wattage Service Factor and check the compressor discharge line to see that it is under 225-F.

CONDENSER TEMP-SPLITS - My Brother's Heil 13-SEER Condensing Unit
1.5-Ton - Rated at 18,400-BTUH,  Condenser fan CFM 1400 (Total Cond. Watts 2221 X's power Factor 0.88 X's= 1955 X's * 3.413 = 6,673-BTUH Motor Heat +18400= Condenser's "Rated Gross Heat Ejection" is 25,073-BTUH / 1400= 17.9-F X's 1.08 = 19-F Temp Rise Cond/Split.

That condenser only gets a 10, rarely up to a 12 temp rise split, the evaporator appears to be under heat-loaded
and/or, an unbalanced heatload on the DX coil's circuitry. Say it is delivering 12,500-Btuh / by a lowered 2000-watts, that gets a 6.25-EER, and insufficient capacity for the heat-gain load!

The new Goodman 13-SEER 1.5-Ton Condenser, 2-Ton Evaporator:
At 675-cfm 450-per/ton cooling | 85-F ODB | 63-IWB | 52% RH | 20-F ID Delta T | 18,600-Btuh
201-psig 100-F = 15-F cond. temp split - larger coil areas | 80-psig suction

The probable cause is "an unbalanced airflow heatload through the evaporator coil. "It's a (Thermo Pride OL 11 oil furnace). Those oil furnaces have a very large round heat exchanger that goes to near the top of the furnace, --due to a low basement ceiling the DX coil sets perhaps illegally close to the heat exchanger causing a few of the coil's circuits to be under heatloaded. Since the liquid refrigerant is not completely evaporated it will cause the outlet line that the TEV sensor bulb is on to be too cold and the TEV will shut-down the flow, which greatly reduces the BTUH capacity of the DX coil and the system. On piston refrigerant control systems, they may flood back liquid which could damage the compressor, unless the system is way under-charged. Thermo Pride could install airflow turning vanes just above the heat exchanger to funnel the air directly into the DX coil, instead of most of the airflow hitting the bottom of the DX's drain pan causing extreme turbulence back-pressure and an imbalanced DX coil circuitry heatload!

The chart split listed below is at Condenser Design conditions: Indoor Return Air 80-F dry bulb 67-F Wet Bulb or 50% Relative Humidity (RH) as you go up to 99% RH the condenser split could increase by up to 6-F; decrease as much as 4-F at a low humidity of 55-F Wet Bulb.

Do your own figuring based on this formula. Motor BTU/hr additive = Watts X's PF x's 3.413 for Btu/Watts additive added to rated BTUH, divided by condenser fan CFM X's 1.08 =  condenser Temp-Split. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers. (A 0.80 factor could be close.) Some of the temp-split figures need correcting, will do ASAP. Most Splits rounded off.

CONDENSER TEMP-SPLITS - Comfortmaker® 12-SEER units - used 0.80 Motor Power Factor

1.5 T  18,400  -18 Split              Cond. CFM 1400     WATTS 2222
2-Ton  24,800  24-F Temp-S    Cond. CFM 1400     WATTS 2659
2.5-T  30,200  21-F Temp-S    Cond. CFM 2000     WATTS 3404
3-Ton  35,600  18-F Temp-S    Cond. CFM 2800     WATTS 4117
3.5 T  42,500  21-F Temp-S    Cond. CFM 2800     WATTS 4554
4-Ton  48,500  19.5-F Split   Cond. CFM 3400     WATTS 4761
5-Ton  59,000  25-F Temp-S    Cond. CFM 3400     WATTS 6969

Air Return - Latent Condenser Split

Page 618, Refrigeration & Air-Conditioning (ARI) Second Edition, C 1987
Those lower SEER units had higher condenser splits than 12-SEER and higher units.
Sorry, I defiled the graph, 90-db outdoor, 80-db indoors with 67 wet bulb or 50% RH represents the condenser splits shown above.  The Evaporator Split is on several other of my pages.

The graph should use 78-F indoor dry bulb (DB) and show the correlative Relative Humidity (RH) to the Wet Bulb (WB)-F readings. Equipment owners could then use an accurate Relative Humidity indicator so they could perform the temperature split diagnosis. Graphs would be specific to the equipment. Condenser CFM should be shown on the metal equipment specification tag and in all spec literature and in the home owners manual.

The condenser fan speeds are slower on several of the 10-SEER Tonnage Models. We are only trying to get a figure to go by for a comparison. When new condensers and Evaporator-coils "are installed on older air handlers" the new, or old, evaporator coils are usually under heat-loaded.
The Base Spec sheets 12-SEER part no. 421 41 33301 03, Feb 2001. These are the Comfortmaker® units, which are nearly identical to Heil® units. [I used the first rating on each tonnage class.] While the "Performance Cooling Data" is listed at a 95-F outside ambient temperature, you can adjust the indoor airflow to get the Nominal BTUH Rating at the customer's normal indoor stat' temp' setting and the most outside temperature/degree operating hours. 

Take the "listed watts" of the compressor and Condenser fan and multiply that wattage by 3.413 to get the BTUH heat additive of the motor then add the listed BTUH of the condenser to it, and then divide by the condenser's CFM. I'm now using the altitude multiplier additive to the initial temp split figure, look up the additive for the height you are above sea level.

With a properly sized system and proper evaporator airflow you will have consistent optimal nominal capacity heat absorption and removal coupled with the requisite longer run-time cycles. I believe that optimal efficiencies, with variable latent/sensible heat loads, could be effectively achieved through the use of computerized control system components.
Below is an outstanding PDF "Basic AC Overview - Specifications VS. Reality"
by John Proctor, P.E., Proctor Engineering Group, LTD:

HVAC TECH PERFORMANCE RATINGS  "AC Specs vs Reality" PDF - It's Worth Your Time

Any of the HVAC companies I list on any of my web pages have nothing to do with the information I post on any of my Web pages nor do I assume any responsibility for how anyone uses that information.
All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for your understanding & communication with contractors & techs.

This information is for the edification of contractors and techs. I am NOT liable for your screw-ups, you are liable for what you do! - Darrell Udelhoven

Darrell's Refrigeration Heating and Air Conditioning - Federal Refrigerant Licensed - Retired Licensed Contractor Amana - Product Information

Please write me if you have anything you'd like to contribute! - Darrell 

Click here to tell a friend about this Web site style="background-color: rgb(204, 204, 255); font-family: helvetica,arial,sans-serif;">
Please feel free to link your web pages to any of mine.

  • Best Practices Guide for residential HVAC retrofit
  • New TEC Energy Conservation Testing Technologies
  • Energy Star  New!

  •    HVAC TALK #1 Residential Forum - HVAC Talk Community
    GARDEN WEB - Heating & Air Conditioning Forum

    DIY Do It Yourself Forum  - "Do It Yourself" TV - New

    HVAC FORUM RULES - "Do It Yourself, - Forum Rules"



    Darrell Udelhoven - udarrell
    Empowerment Communications
    Covering The Real Political Issues
    Posted: 11/13/03; Updated: 04/24/11