Air Conditioning Repair Troubleshooting 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.