General

Troubleshooting Tips

Troubleshooting

23.8.4 General Troubleshooting Tips

1. This program is not intended to cover troubleshooting of all the components used in a heat pump system. The student should have knowledge of air conditioning systems operation, components, and troubleshooting skills.

2. Before attempting to service any heat pump, take time to understand the particular system being addressed.

3. Without understanding how an individual unit operates, it is nearly impossible to service the unit with a systematic approach.

4.Asking the following questions before attempting to service any unit should help to pinpoint the problem more quickly and easily.

 5.Does the problem occur during heating or cooling?

Troubleshooting

23.8.4

6. Is the reversing valve energized in heating or cooling mode?7. Does the problem occur due to the unit not defrosting properly?8. What type defrost system does this heat pump use?9. Is the problem really caused by a malfunction or is the unit functioning

normally?10.While the last question may seem somewhat peculiar at first, it is a given that

some customers call for service even if the unit is operating normally.1. Sometimes, the customer may hear a strange sound (shifting of the

reversing valve) or may feel cold air coming from the vents, which may be a normal condition during the defrost cycle.

2. The customer may get excited or worried about the fog or mist coming out of the outdoor section during the defrost cycle.

3. Do not put on the gauges on the system unless it is deemed absolutely necessary; the refrigerant charge is critical for heat pumps.

Troubleshooting

23.8.4

The split is the difference between the entering (return) and leaving (supply) air at the coil acting as an

evaporator.

When the space contains excessive humidity, the split drops.

The system is absorbing more latent heat as well as sensible heat when indoor air has high humidity.

Troubleshooting

23.8.4 Evaporator Temperature Split

1.The system will run with the required temperature split only at the design conditions.

2.The temperature split across the evaporator is a design factor based on the sensible heat ratio that is calculated from the heat load of the structure and required CFM of air.

3.As the indoor relative humidity increases, the temperature split will decrease.

Troubleshooting

23.8.4

Determine, Measure & Record1. Condenser fan CFM (use manufacturers’ data).2.Condenser entering air temperature.3.Condenser leaving air temperature. (Measure to the nearest 10th)4.Line Voltage at the condensing unit.5.Measure Total Amperage of the condensing

unit.

Net Cooling Capacity = 1.08 x CFM X ∆T – Motor Heat in Btu/hr

Troubleshooting

23.8.4 Net Cooling Capacity

1.This is a simple check to measure the total sensible heat being dissipated by the outdoor system.

2.It can be used on a heat pump or cooling system.

3.This test is a measurement of the total sensible heat.

4.The outdoor fan CFM must come from manufacturer’s data.

5.The design of the fan discharge areas from one system to another will vary too much to use an average area for CFM calculations.

6.The Btu capacity of a system can also be calculated by using the indoor air flow (this method is most difficult).

7.Calculating the total Btu capacity involves measuring the air flow, temperatures, and a psychometric chart to find latent / sensible heat Btu.

Troubleshooting

23.8.4

(1.08 x 3000 x 9) = 29,160 Btu – (232.4 x 9.5 x 3.41 x 0.9) = 6,776Btu

Btu =29,160 – 6,776

Net Btu = 22,384 (±2000 Btu)

∆T = Condenser leaving air temperature minus the condenser entering air temperature.

Motor Heat = Volts x Amps x 3.41 x Power Factor(use actual power or 0.9 if not known)

Net cooling Capacity 1.08 x CFM X ∆T – Motor Heat in Btu/hr

Troubleshooting

23.8.4 Net Cooling Capacity

1.The heat from the coil is all sensible heat given up to the air plus the heat from the electrical loads.

2.Sensible Heat = 1.08 or (1.1 rounded off) x CFM X temperature difference.

3.Electrical Motor Heat = Volts x Amps x 3.41(Btu per watt) x Power Factor (Average is 0.9, higher efficiency equipment will be a little higher number.)

4.Due to the test instruments used in the field, there can be a + or – 2000 Btu error.

Troubleshooting

23.8.4

Refrigerant should be weighed in for optimal efficiency.System superheat or sub-cooling should only be used in the cooling mode.Charging in the heating mode by temperatures & pressure are not accurate.

Refrigerant Charge

Troubleshooting

23.8.4 Refrigerant Charge1.Use the manufacturers’ data and specifications for servicing and

troubleshooting a specific unit. 2.Higher efficiency heat pumps have different requirements and

specifications. 3.There is no longer a set charging formula (such as ambient plus 30 F ⁰

converted to pressure). 4.All suggested readings are based on the unit operating in a normal

environment. If the unit is operating out of its designed range, the readings are also out of range.

5.The suction pressure may be greater because the load is greater, not because the unit is malfunctioning.

6.It is almost impossible to tell how much refrigerant is in the system that has a suction accumulator in the heating mode.

7.Plus or minus ½ ounce of refrigerant can make a difference in capacity.

Troubleshooting

23.8.4

Sub-cooling varies from 10ºF to 20ºF at the exit of the condenser depending on model design.

 System super heat varies as the indoor or outdoor temperature changes.

Low outdoor temp. = High super heat

High outdoor temp. = Low super heat

Troubleshooting

23.8.4Refrigerant Charge

1.Superheat can be used to check the refrigerant charge as previously shown only in the cooling cycle.

2.Sub-cooling is the difference between the liquid line temperature at the condenser outlet and the condensing temperature.

3.Sub-cooling measures how much additional cooling the liquid refrigerant has received after it has condensed into liquid.

4.Sub-cooling should be checked based upon the manufacturer’s specifications.

Troubleshooting

23.8.4

Discharge line temperatures average 175ºF to 225ºF.

Excessive discharge temperatures are those above 225 degrees F.

Caused by high super heat from a lost of refrigerant or malfunctioning metering device.

Refrigerant Charge

Troubleshooting

23.8.4 Refrigerant Charge

1.Excessive discharge temperatures must be controlled and should never be more than 225 degrees F.

2.With Refrigerant 22, the head pressure should never be in excess of 300 psig.

3.Excessive discharge temperatures may cause burnt oil, compressor valve damage, and bearing problems, if left unattended.

Troubleshooting

23.8.4

Evaporator Outlet Air Temperature, Heating Mode:

85ºF to 105ºF (Depends on the outdoor air temperature).

Suction Pressure is equal to Wet-bulb temperature minus 26 degrees F.

Heating

Troubleshooting

23.8.4 Heating 1. The supply air leaving a heat pump is approximately 95⁰F when

the heat pump is operating with an outdoor temperature of 55⁰F. 2.As the outdoor temperature continues to drop, the supply air

temperature will also drop.

3.If the unit is overcharged, the suction pressure may be higher. 4.In the heating mode, the suction or discharge pressure may not

change while adding refrigerant.

5.The pressure could remain the same whether the suction accumulator has ½ ounce or 3lbs. of refrigerant in it.

6.The only safe way to charge a heat pump in the heating season is to charge by weight.