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1 If you d like to be able to print this file out to study off-line or use on the job, a printable version is available for an administrative fee of $3.97 USD. To download the unlocked file, click here. Otherwise, you can continue reading the file on the following pages.

2 Take a look at the evaluation diagram. When you re troubleshooting a system, every factor in the diagram will affect the system s capacity, so take every pressure and temperature, and evaluate them all at the same time. Build a complete picture of the system s operating characteristics, and think of it as a snapshot or X-ray of the whole system. If you re troubleshooting a system that is running but possibly has low cooling capacity, check the thermostat, make sure the coils and filters are clean and not obstructed, that the fans are running and some air is flowing through the coils, then hook up your gauges and check the following pressures and temperatures.

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4 Step 1. Check subcooling. On almost all vapor compression systems, with a few exceptions, Look for subcooling at the outlet of the condenser or receiver. If subcooling exceeds 15, the system is probably overcharged, or it may have mismatched components installed. Remove refrigerant to 15 or less sub cooling, then check and evaluate other factors in the system: Check superheat, air flow, temp splits, etc. If there is no measurable sub cooling, the system is probably undercharged or it may have mis-matched components installed. Step Check and evaluate system components, locate and repair any obvious leaks. 2. Charge in refrigerant to correct sub cooling. Check superheat. NOTE: Check superheat on the suction line, 6-12 from the inlet to the compressor. On almost all vapor compression systems, with a few exceptions, look for 20 superheat minimum, 30 superheat maximum. Step 3. Check and evaluate operation of the entire system.

5 MISCELLANEOUS TIPS: The compressor discharge line temperature should not exceed 215. High superheat can affect this. To check for suspected air or non-condensables, Shut down the system for 15 minutes and let the pressures equalize. If the high side pressure is equivalent to a temperature that s higher than the temperature of the condenser coil, it is an indication of non-condensables in the system. If you suspect a leak, find it and repair it.

6 TIPS ABOUT SUPERHEAT NOTE: Superheat readings will be most accurate when taken when the system is running near design conditions, best when within 5 of desired temperature. Measure superheat 6-12 from the compressor inlet. Less than 20 of superheat is too low and risks liquid flood back. More than 30 of superheat is too high, and provides insufficient cooling to the compressor. On systems with a suction to liquid heat exchanger, of superheat at the compressor inlet is normal, and superheat on these systems will vary. On a cap tube or orifice system, at or near design conditions, If superheat is less than 20, remove refrigerant until superheat is more than 20. If subcooling is too low now, check compressor efficiency. On a cap tube or orifice system, Superheat will rise and fall with the space temperature. Evaporator pressure may be slightly higher at higher space temperatures, but usually stays relatively steady. Superheat will rise and fall with changes in the evaporator inlet air temperature. On a TXV system, If superheat is less than 20, and other system factors are OK, check compressor efficiency. If the compressor is OK, the TXV is flooding. Check bulb mounting, valve adjustment, then if necessary, replace the TXV. Also on a TXV system, Superheat remains relatively steady. Evaporator pressure rises and falls with changes in the inlet air temperature. NOTE: On cap tube, orifice, and TXV systems, If inlet air temperature is too high, superheat will be high.

7 TIPS ABOUT SUBCOOLING Almost all DX systems run with a range of sub cooling. With 15 sub cooling, If superheat is more than 30, the system is probably restricted. Evaluate all other system factors. NOTE: Some systems are designed to run without sub cooling. Check the manufacturer s specifications. RESTRICTION If a restriction is suspected, check the liquid line and drier for a temperature drop. If temperature does not drop more than 5 along it s length, the metering device is restricted That is IF Superheat is over 30 and sub cooling is in the normal to high range. If the metering device is a cap tube or orifice, it s possibly plugged. If it s a TXV, check the inlet screen. Check the drier carefully.

8 TIPS ABOUT CAP TUBE OR ORIFICE SYSTEMS Charge to correct superheat. If the system is cooling, it is most accurate to check superheat and sub cooling at design temperatures and conditions. Between 20 and 30 of superheat with measurable (less than 15 ) sub cooling, is the correct charge. Subcooling will usually be Superheat will usually be If superheat is more than 30, add refrigerant until superheat is less than 30 or sub cooling is 15, whichever is first. NOTE: If space temp is higher than design point, superheat will be high. Low Temp systems will usually have a suction to liquid heat exchanger. At design conditions, Superheat in these units may be as high as Look for 50 to 60 of superheat at the compressor inlet. Less than 20 of superheat is not acceptable. On Medium Temp systems, at design conditions, look for of superheat, 5-15 of sub cooling. On High temp or A/C systems, Superheat should be At design conditions, evaporator pressures should be equivalent to: For low temp, below space temp, 10 below evaporator inlet air temperature. For medium temp, below space temp, 10 below evaporator inlet air temperature. For high temp - A/C, below space temp. When trouble shooting a system, given the above design conditions, A lower than design evaporator pressure is equivalent to high superheat, A higher than design evaporator pressure is equivalent to low superheat.

9 TIPS ABOUT TXV SYSTEMS At design conditions, subcooling should be 10-15, superheat should be If there s no sub cooling, and more than 30 of superheat, the charge is probably low. Charge to correct sub cooling, IF superheat is now less than 30, the system was undercharged. On hi temp or A/C systems, Evaporator pressure should be equivalent to at least 35 below evaporator inlet air temperature. If not, compressor capacity may be low. On medium and low temp systems, Look for 15 or less sub cooling, of superheat. Evaporator pressure should be equivalent to at least 10 below evaporator inlet air temperature.

10 TIPS ABOUT EVAPORATOR CHARACTERISTICS On high temp and A/C systems, at design conditions, a air temperature drop across the coil is ideal, 20 max. 25 is acceptable only if all system factors are balanced and the coil is not icing up. NOTE: Above does not apply to systems with capacity control. In units with capacity control, temperature drop across the evaporator may exceed 20. On medium and low temp systems, at design conditions, the air temperature drop across the coil is usually 4-8. On A/C systems, evaporator pressure should be equivalent to at least 35 below return air temperature. If it isn t, the compressor may not have the capacity to handle the load. Note: Higher pressures are normal on high efficiency units. For medium and low temp systems, at design conditions, evaporator pressure should be equivalent to at least 10 below space temp. If space temp is higher than design condition, evaporator pressure may be higher than normal.

11 TIPS ABOUT CONDENSER CHARACTERISTICS For an air cooled condenser, Look for a temperature difference between entering and leaving air. A temperature difference across the coil of more than 30 is too high. Check air flow through the coil. Condensing pressure should be equivalent to at least above ambient. If it is less than 20 above ambient, the condenser coil may be too large, the compressor may be too small, the compressor may be inefficient, or may have lost capacity. Water cooled condenser characteristics: First, always check the manufacturer s specifications. Most water cooled condensers are designed for entering water to be in the temperature range of 75 to 95, 85 is ideal. Water temperature rise through the condenser is normally in the range of 10. Condensing pressure should be equivalent to leaving water temperature A difference of more than 20 between condensing saturated temperature and entering water temperature is too high. If you find this, Check for insufficient water flow or a dirty condenser, Check operation of the water regulating valve, if installed, Verify that the entering water temperature is in the normal range. As a general guide for high efficiency units, If EER = OR LESS, Air temperature rise across the condenser Shouldn t exceed Air temperature drop across the evaporator shouldn t exceed The difference between evaporating temperature and evaporator inlet air temperature shouldn t exceed

12 COMPONENT BALANCE EVALUATION Subcooling should be 10-15, 15 max. Superheat should be in the range of 30 maximum, 20 minimum. Condensing pressure should be equivalent to approximately above ambient. At or near design condition for the space: Evaporator pressure should be equivalent to: For high temp, below space temperature. For medium and low temp, below space temperature. Compressor - vs.- condenser coil, If you re troubleshooting low condensing pressures and temperatures, condensing pressure should be equivalent to at least 20 higher than ambient. If it isn t, the coil may be too large for the compressor, or, the compressor capacity is not enough for the size of coil. NOTE: Condensing pressure will be low at low ambient conditions. Compressor -vs.- evaporator: If you re troubleshooting low evaporator pressures, and if evaporator pressures are not at least as specified above, evaporator capacity may exceed compressor capacity. SO, At design space conditions (when the room is cool), high evaporator pressure, with low condensing pressure, can be an indication of low compressor capacity. If you have a very low air temperature drop through the evaporator, with a low air temperature rise across the condenser, unusually high evaporator pressure, unusually low discharge pressure, and a low compressor amp draw, your compressor probably has failed valves.

13 Oil Pump & Oil Pressure: Net oil pressure is oil pump discharge pressure minus saturated suction pressure (in the crankcase). If there is low or no net oil pressure, If oil level is correct, and oil is not foaming, The problem is the oil pump or compressor. A compressor that is leaking oil internally will still show net oil pressure. A malfunctioning oil pump will almost always show no net oil pressure. Compressor test: Pinch off suction line or liquid line or close isolation valve. Compressor should pull down to at least 20 inches of vacuum. If it doesn t pull down to at least 15 hg within 2 minutes, it has lost efficiency. You may have to release high side pressure to an empty recovery can to get the compressor to pump down. If the compressor pumps down efficiently this way, it is probably still good. If you re using a standard multi-tester and get a readable resistance reading from a compressor terminal to ground, even if the reading is in Megohms, you have a grounded winding. This must be verified with a Megger.