Darrell's Air Conditioning Trouble Shooting Chart

First, always check for Return Air/Supply Air duct leaks, seal them with approved mastic, check CFM airflow rate and that the coil fins and blower wheel blades are clean! "Check for Insufficient Air Flow Across Evaporator Coil" - Check for: dirty filter, dirty lint clogged evaporator, blower speed tap selected, or belt and speed adjustments, blower motor, check any belts for wear and proper tension, dirt lint loaded blower wheel, and out of specs or wrong rated run capacitor.

Check airflow system static pressure. Verify Blower Performance --by checking blower air handler "Static Pressures with the specific model's Blower Curve Charts." At a specific heatload condition, Optimize the conditioned space's heatload on the evaporator coil to optimize the rated Btu/hr and EER, and/or SEER Ratings.

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

Where air handlers' are 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 AC system with attic heat!
Airflow has to be optimal & within specs before the refrigerant charge can be correctly charged!

Check Return Air (RA) at grille & at entry of blower for heat gain, due to hot Return Air leaks.
Where airhandlers' 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 AC system!

For efficiencies sake measure the Return Air duct/chase area. If it's a round duct measure the inside diameter, I'll give you the sq. ins. formula on another pages; if square or rectangular multiple the two dimensions for sq. in. area. The sq.in. Return Air throughput ducting area should equal or exceed the Supply Area ducting. In the far north smaller A/C units Verses the new larger heating blower units can mean too much CFM for the A/C's smaller BTUH capacity. Thermostatic Expansion Valves (TEV / TXV) systems should be set for a minimum 10 Degrees Superheat.

NOTE on 3 & 5 Above: If suction is high & head is low it is not necessarily an inefficient compressor, it could be (3) three.

"An oversized orifice or overfeeding TXV refrigerant metering device" could cause high suction & low head due to normal compressor pumping capacity being incapable of keeping up. An oversized unit might handle the sensible load but never do anything with the latent load as the conditioned space temp falls.

"Overcharging" will raise suction pressures & E-Coil temperatures & though it may raise head pressures, it does not always raise head pressures. The reason for this is that it reduces the capacity of the evaporator to absorb both latent & sensible heat & therefore reduces the actual heatload on what may possibly be an oversized over-capacity condenser coil.

Of course, an inefficient compressor could cause this problem; however, I would always do the Superheat & Subcooling checks & look for an overfeeding metering device as well as an overcharged system, along with other possible causes, before ever condemning a compressor.

(8) NOTE: Refrigerant Overcharge: amp draw is HIGH when under a heavy heatload and can be LOW when overcharged but under a light heatload; both the condenser and evaporator are then overloaded with liquid and there is not enough of a heatload to evaporate sufficient amounts of refrigerant in the E-Coil to INCREASE PRESSURES and pumping WORK.

After any duct work or other changes and before you make any recheck tests, it is very important that your condenser coil, evaporator coil, and indoor blower wheel be squeaky clean.

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

Target Temperature Split for Airflow Chart
Print the linked pdf TEMP-SPLITS chart only, ignore the super heat chart.
Upper right corner, blank out RA WB Temps above RA DB Temps, PC kept figuring the errant ratio.

First, thoroughly seal all ductwork with an approved mastic!

INTRODUCTION TO TOTAL COOLING PERFORMANCE;
How installing a 3-ton system can become a 1.5-ton system of actual delivered cooling (SURPRISE!):
http://epb1.lbl.gov/residential/cool.html

To get the gross BTUH Heatload the Evaporator (DX) Coil is absorbing (which includes both latent, sensible heat) (These are ARI Formulas)
First, determine the Gross Rated BTUH the condenser is ejecting.
Condenser’s Gross Btuh = Condenser’s rated CFM X’s Temp Split X’s 1.08

CONDENSER TEMP-SPLITS - My Brother's Heil 12-SEER Condensing Unit
1.5-Ton - Rated at 17,500-BTUH, Condenser fan CFM 1400 (Total Cond. Watts 1591 X's power Factors0.90 X's= 1432 X's * 3.413 = 4887-BTUH Motor Heat additive +17,500= MotorPower "Rated Gross Heat Ejection" is 22,387-BTUH / 1400= 15.99-F x 1.08= 17.27 Temp Rise Cond/Split. His condenser only gets a 10 to 12 temp rise split, the evaporator appears to be under heat-loaded or, an unbalanced heatload on the DX coil's circuitry.

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 circuitry DX coil heatload!
His unit could also have some low temperature solder trapped on the screened entrance to the TEV evaporator metering device. If there is a gurgling noise& temp drop there, any restriction there would also lower the capacity of the cooling coil.
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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.
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Too many do not properly purge & evacuate contaminated central air conditioning systems.

The Triple Evacuation Method is normally done on refrigeration systems, R-410a systems require it on 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 400 microns, valve off vac pump, & again break the vacuum with dry nitrogen

6) Evacuate system to 400 microns and & then Check to see if it holds. (Recharge with fresh clean refrigerant)

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

If a vacuum pump will not evacuate a system below 1500 microns there is a problem with the pump itself, a leak in the system, or moisture in the system. Moisture is most likely because water vaporizes at 1500 microns.

Many HVAC contractors will consider this excessive time & effort for contaminated residential air conditioning systems, however it is a must for low temp applications.

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.

When a system has been evacuated below 500 microns, the pump is valved-off with the micron gauge connected, if the vacuum rises to 1500 microns and stops, there is moisture remaining in the system. If it rises above 1500 microns & continues to rise there is a leak. You should allow at least 15 minutes after the pump has been shut off an accurate micron gauge reading. When a system will not evacuate below 1500 microns there is either a lot of water or there is a system leak.

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. (Always, check voltage and amp draw!)

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.

Below is an outstanding PDF "Basic AC Overview - Specifications VS. Reality"
by John Proctor, P.E., Proctor Engineering Group, LTD:

DISCLAIMER:
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 garantee its accuracy or 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

Air Conditioning System Trouble Shooting Superheat and Subcooling VERY IMPORTANT !

AIR-CONDITIONER RUNNING TOO MUCH
3.5-ton system getting less than 1.5-ton of capacity! Overcharged - plus

Optimizing the Evaporator BTU/hr Heat-Input Important!

Determining Your Air Conditioner's Actual BTUH Output New- Surprises!

"Higher" or "Lower" than "Normal" (PRINT CHART)	Low-Side	SUCTION	High-Side	Liquid-Line	Cond.-Unit
NORMAL - (norm) - LOW - HIGH - Variable	Suction-PSIG	Super-Heat	Head-Pres.	SUB-Cooling	Amp-Draw
(1) Suction Line Restriction - Upstream Between Service Port & E-Coil	LOW	HIGH	LOW	norm	LOW
(1a)Suction Line Restriction - Downstream from Service Port At Compressor screen TXV	Normal to High	HIGH	LOW	norm	LOW
(2) Restrictive metering orifice; TXV Starving Coil; liquid line Restriction	LOW	HIGH	N-low	norm	LOW
(3)Evaporator orifice oversized or bypassing - or TXV Overfeeding - Normal Charge	HIGH	usually - low	LOW	norm - low	NORMAL-LOW
(4) Hot gas Disc. Line Restriction	HIGH	HIGH	HIGH	NORMAL	HIGH
(5) Inefficient Compressor - Also, see (3) Above	HIGH	HIGH	LOW	LOW	LOW
(6) Unbalanced heatload on Evaporator Circuits	LOW	LOW	LOW	Norm	LOW
(7) Insufficient Evap. Airflow, or Heatload	LOW	LOW	LOW	LOW	LOW
(8) Refrigerant Overcharge- High or Low pressure -Variable according to heatload non-TXV	Norm - High	LOW	Varies by Load	HIGH	Varies/Low
(9) Insufficient Charge - piston orifice	LOW	HIGH	LOW	LOW	LOW
(9a) Insufficient - Fairly Low Charge with TXV Wide Open	Normal	HIGH	LOW	LOW	LOW
(10) Excessive Evaporator Heat Load - Latent & Sensible - High Latent	HIGH	HIGH	HIGH	Usually Low	HIGH
(11) Very High Temp Ambient Air Entering Condenser or dirty - Low condenser airflow	HIGH	HIGH	HIGH	norm	HIGH

Air Conditioning System Trouble Shooting Superheat and Subcooling VERY IMPORTANT !

AIR-CONDITIONER RUNNING TOO MUCH 3.5-ton system getting less than 1.5-ton of capacity! Overcharged - plus

Optimizing the Evaporator BTU/hr Heat-Input Important!

Determining Your Air Conditioner's Actual BTUH Output New- Surprises!

AIR-CONDITIONER RUNNING TOO MUCH
3.5-ton system getting less than 1.5-ton of capacity! Overcharged - plus