Unit 41 Troubleshooting

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Unit 41 - Troubleshooting
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41.1. Introduction

• a. Troubleshooting air conditioning equipment
  involves both the mechanical and electrical
  systems
• b. Symptoms may overlap
• c. Technicians must diagnose problems correctly

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41.2. Mechanical Troubleshooting

• a. Gages and temperature-testing equipment are
  used when performing mechanical troubleshooting
• b. The most common refrigerant used in air
  conditioning equipment is R-22
• c. R-22 temperature chart is printed on each gage
  of the gage manifold set for determining the
  saturation temperature for the low and high side
  pressures of the system

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41.3 Gage manifold usage

• a. Displays the low and high side pressures while
  the unit is operating
• b. These pressures can be converted tot he
  saturation temperatures for the evaporating
  refrigerant and the condensing refrigerant by
  using the pressure and temperature relationship
• c. Take the pressure and temperature readings at
  the condensing unit suction line to determine
  system performance when performing a superheat
  check on the evaporator
• d. The high-side gage may be used to convert
  pressures to condensing temperatures
• e. Gage manifolds are used whenever the pressures
  need to be known for the system
• f. Two types of pressure connections
• 1. Schrader valve
• 2. Service valve
• g. Schrader valve is a pressure connection only
• h. Service valves can be used to isolate the
  system for service

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41.4 When to Connect the Gages

• a. Gage manifolds should not be connected every
  time a system is serviced
• b. Small amounts of refrigerant escape each time
  the gages are connected and removed from a sealed
  system
• c. Short gage hoses will limit the amount of the
  refrigerant loss
• d. Connecting the gages to Schrader valve service
  ports with a small hand valve is another method
  of limiting the amount of refrigerant loss when
  gages are removed

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41.5 Low Side Gage Readings

• a. Used to compare the actual evaporating
  pressure to the normal evaporating pressure
• b. The low side reading verifies that the
  refrigerant is boiling at the correct temperature
  for the low side of the system at some load
  condition
• c. Standard efficiency systems usually have a
  refrigerant boiling temperature of about 35
  degrees F cooler than the entering air
  temperature at the standard operating condition
  of 75 degrees F return air with 50 humidity
• d. Space temperature out of these ranges will
  cause an oversized load on the evaporator
• e. Under oversized loads, the evaporator is
  absorbing an extra heat load of sensible and
  latent heat from the moisture in the air
• f. Technicians should wait sufficient time for
  system to reduce the load before determining if
  the equipment is functioning properly
• g. Gage readings when the system is operating in
  or close to design range will verify the system's
  true performance

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41.6. High Side Gage Readings

• a. Gage readings from the high side of the system
  are used to check the relationship of the
  condensing refrigerant to the ambient air
  temperature
• b. Standard air cooled condensers condense the
  refrigerant at no more than 30 degrees F higher
  than the ambient temperature
• c. Make sure to check the outside actual air
  temperature
• d. High efficiency condensers perform the same as
  standard efficiency condensers, except they
  operate at lower pressures and condensing
  temperatures
• e. High efficiency condensers normally condense
  the refrigerant at a temperature as low as 20
  degrees F higher than the ambient temperature

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41.7 Temperature Readings

• a. Temperature readings can be very useful when
  checking the performance of air conditioning
  equipment
• b. Temperature leads can be attached to the high
  and low side lines for determination of the
  system's superheat and subcooling temperatures
• c. It is important that the leads be insulated
  from the ambient air
• d. Temperatures will vary from system to system,
  so technicians should be prepared to record and
  accurately evaluate the readings
• e. Common temperatures used for evaluation are
• 1. Indoor air wet and dry bulb temperatures
• 2. Outdoor air dry-bulb temperature
• 3. Suction-line temperature
• 4. Condenser outlet-line temperature
• 5. Compressor discharge-line temperature
• f. Inlet air temperature
• 1. Necessary to know to determine the load the
  evaporator is dealing with
• 2. A wet-bulb reading for determining the
  humidity is necessary
• 3. Dry-bulb temperature reading is necessary
• g. Evaporator outlet temperature
• 1. Evaporator outlet air temperature is seldom
  important
• 2. Outlet dry-bulb temperature will normally be
  about 20 degrees less than inlet air temperature
• 3. The temperature drop across an evaporator coil
  is about 20 degrees F when operating at typical
  operating conditions of an inside air temperature
  of 75 degrees F and 50 relative humidity return
  air
• 4. If the conditioned space temperature is high
  with high humidity, the temperature drop across
  the coil will be much less because of the
  latent-heat load of moisture in the air

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41.8 Charging Procedures in the Field

• a. The correct charge of a system consist of
  enough refrigerant in the following
• 1. The evaporator
• 2. The liquid line
• 3. The discharge line between the compressor and
  condenser
• 4. The suction line
• b. When the system is operating correctly under
  design conditions, there should be a prescribed
  amount of refrigerant in the condenser, the
  evaporator, and the liquid line
• c. The amount of refrigerant in the evaporator
  can be measured by superheat
• d. The amount of refrigerant in the condenser can
  be measured by subcooling
• e. The amount of refrigerant in the liquid line
  may be determined by measuring the length and
  calculating the refrigerant charge
• f. Following are methods for field charging
  different types of equipment
• g. Fixed-bore metering devices - capillary tube
  and orifice type
• 1. Fixed-bore metering devices do not throttle
  the refrigerant like a TXV
• 2. They allow refrigerant flow based on the
  differences in the inlet and the outlet pressures
• 3. Best method for checking or adjusting a
  system's charge is to follow the manufacturer's
  recommendations
• 4. If the manufacturer's recommendations are not
  available, use the following method
• 1. Simulate typical operating conditions
• 2. Reduce the airflow across the condenser to
  cause the head pressure to rise to simulate a 95
  degree F outside air temperature
• 3. For an R-22 system under these conditions, the
  head pressure would be around 278 psig
• 4. Under these conditions with a line set of 10
  to 30 feet, the evaporator superheat should be 10
  to 15 degrees F

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41.9 Electrical Troubleshooting

• a. The volt-ohm-milliammeter (VOM) and the
  clamp-on ammeter are the primary test instruments
  used for troubleshooting electrical problems in
  air conditioning equipment
• b. You need to know what the readings should be
  to know whether the existing readings are correct
  or not
• c. The power for the control voltage is stepped
  down to 24 volts by a transformer
• d. Begin any electrical troubleshooting by
  verifying that the power supply is energized and
  that the voltage is correct
• e. If the power supply voltage is correct, move
  on to the various components

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41.10 Compressor Overload Problems

• a. When the compressor overload protector is
  open, touch the motor housing to see if it is hot
• b. If you cannot hold your hand on the compressor
  shell, the motor is too hot
• c. The compressor can be cooled by running cold
  water over the top of it or by disconnecting it
  and allowing it to cool
• d. When cooling a compressor by running water
  over it, it may take 30 minutes or longer for one
  to cool that has a tripped overload

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41.11 Compressor Electrical Checkup

• a. Check the motor windings with an ohmmeter
• b. Refer to the manufacturer's specifications for
  correct winding resistance values
• c. The compressor may have a shorted winding

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41.12 Troubleshooting the Circuit Electrical
Protectors - Fuses and Breakers

• a. Open circuit breakers or blown fuses should be
  treated with caution
• b. Compressors and fan motors have protection
  that will normally guard them from minor problems
• c. The breaker or fuse is for large power surges
  in the circuits
• d. Do not reset or replace a tripped breaker of
  fuse without trying to determine what caused the
  fuse to blow or the breaker to trip
• Preventive Maintenance
• a. Involves indoor and outdoor airsides and
  electrical circuits
• b. If the fan is dirty the coil is also dirty
• c. Coil can usually be cleaned in place with
  specially designed chemicals
• d. Follow manufacturer's directions on chemical
  containers
• e. Back washing is good practice
• f. Do not use hot water or steam to clean
  refrigeration equipment
• g. If the coil must be removed for cleaning, the
  system may be pumped down
• h. Outdoor fan motors need to be lubricated
• i. Outdoor fan blade should be secure
• j. Outdoor coil is much easier to clean than the
  indoor coil
• k. Check water bleed on water cooled systems
• l. Make certain water treatment is correct
• m. Contactors and relays should be inspected
• n. All wiring connections should be tight

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41.13 Service Technician Calls

• a. Service call 1
• 1. Customer complaint unit runs continuously and
  does not cool well
• 2. Problem low refrigerant charge (R-22)
• 3. Technician notices
• 1. Space temperature is 80 degrees, thermostat
  set at 72
• 2. Space is humid
• 3. Indoor fan is running and air flow is adequate
• 4. Condenser fan is running
• 5. Condensing unit discharge air is not warm
• 6. Compressor is not running and is hot to the
  touch
• 7. High and low side pressures are 144 psig (80
  degrees)
• 8. A low charge is suspected
• 9. Compressor is checked and the winding
  thermostat is open
• 4. Electrical components are covered and the
  compressor is cooled down with a water hose
• 5. The system is restarted and the suction
  pressure drops to 40 psig (the normal suction
  pressure should be about 70 psig)
• 6. Outside ambient is 90 degrees 90 degrees 30
  degrees 120 degrees (condensing temperature)
  120 degrees corresponds to 260 psig
• 7. Space temperature is 80 degrees 80 degrees -
  35 degrees 45 degrees (boiling temperature) 45
  degrees corresponds to 76 psig
• 8. The unit is charged to the correct levels and
  the operation checked
• b. Service call 2