RSI PHASE 8 MECHANICAL TEST WITH COMPLAINTS & RESOLUTION
Correct answer: Air/Non Condensables
Problem #1 •Complaint: Inadequate Cooling, •Type Unit: Package System, •Symptoms: Ambient air temperature 100°F, Suction pressure 82 psig, Discharge pressure 335 psig Compressor hotter than normal, Compressor amps higher than normal, Temperature split across condenser high, Temperature split across evaporator low, Return air temperature 86°F, Supply air temperature 71°F, Suction line warmer than normal, After shutdown high side gauge reads 220 psig,
Low Charge
Problem #10 •Complaint: No Cooling •Type of Unit: Split System Straight Cool •Symptoms: Suction pressure Low Head pressure Low Superheat High Sub-cooling Low Compressor running hot
TXV Stuck Open
Problem #11 •Complaint: Little or No Cooling •Symptoms: Ambient air temperature 100°F Low side pressure 88 psig High side pressure 310 psig Condensing unit is noisy Superheat is low Evaporator, fan blades & air filter are clean Sub-cooling is low
Bad Compressor
Problem #12 •Complaint: Very Little Cooling •Symptoms: Ambient air temperature 90°F Low side pressure 110 psig High side pressure 150 psig Evaporator split is low Compressor amp draw is lower than normal Condenser split is only 7°F
Correct answer: ***Any of them*** Dirty Filter Dirty Fan Wheel Dirty Evaporator Coil
Problem #14 •Complaint: Unit runs too much and air at the supply vents is too cold •Type Unit: Package System •Symptoms: Ambient air temperature: 95°F Return air temperature: 81°F Low side pressure: 56 psig High side pressure: 260 psig Suction line temperature: 36°F Liquid line temperature: 105°F Evaporator fan motor drawing lower amps than normal A light layer of frost on 90% of evaporator coil
TXV Overfeed
Problem #15 •Complaint: Very Little Cooling •Type Unit: Package System •Symptoms: Ambient air temperature: 101°F Low side pressure: 90 psig High side pressure: 350 psig Static pressure: 200 psig Low sub-cooling Low superheat Sweat on suction line There are no signs of any restrictions Return air temperature: 85°F
Correct answer: Liquid Line Restriction
Problem #16 •Complaint: Insufficient Cooling •Type of Unit: Package System •Symptoms: Ambient air temperature 91°F Low side pressure 62 psig High side pressure 210 psig Static pressure 170 psig Compressor amps are low Compressor running hotter than normal Sub-cooling is 20°F Supply air is warm Liquid line temperature at the TXV inlet is 70°F
Shortage of Refrigerant
Problem #17 •Complaint: Very Little Cooling •Type Unit: Package System •Symptoms: Ambient air temperature 95°F Low side pressure 54 psig High side pressure 220 psig Static pressure 182 psig Liquid line temperature at the condenser is 106°F Suction line temperature at the TXV bulb is 49°F Evaporator has a definite frost line at the point of refrigerant saturation
Correct answer: Any one of them - see below Dirty Fan Wheel (Squirrel Cage) Evaporator Fan Speed Too Slow Dirty Evaporator Coil
Problem #18 •Complaint: Unit Cools OK but Humidity is Too Low •Type Unit: Package System •Symptoms: Ambient air temperature 111°F Low side pressure 62 psig High side pressure 334 psig Static pressure 230 psig Suction line temperature 42°F Liquid line temperature l32°F Return air temperature 80°F Supply air temperature 55°F Return air filter is clean
Undercharged
Problem #19 •Complaint: Very Little Cooling •Type Unit: Package system •Symptoms: Ambient air temperature 1l0°F Low side pressure Low High side pressure Low Static pressure 229 psig Compressor Hot with Low Amps Low Sub-Cooling High Superheat
Correct answer: Restricted Liquid Line Drier
Problem #2 •Complaint: Not Cooling •Type Unit: Package System •Symptoms: Ambient air temperature: 95°F Static pressure 182 psig Suction pressure: 68 - Drops down into a vacuum Discharge Pressure: 278 psig - decreases while low side pressure drops into vacuum Sub cooling: high A temperature drop can be felt across the liquid line drier
Overcharge
Complaint: Unit Runs Too Much Type Unit: Package System Symptoms: Ambient air temperature: 109°F Return Air Temperature: 82°F Static Pressure: 221 psig Sight Glass: Clear Low Side Pressure: 78 psig High Side Pressure: 350 psig Suction Line Temperature: 50°F Liquid Line Temperature: 120°F Compressor Amps: High Heavy Sweating on the Suction Line
** Correct Answer Any of these answers* Dirty Filter You Answered Dirty Evaporator Coil Dirty Fan Wheel
Complaint: Unit Runs Too Much, Air at Supply Vents Too Cold Type Unit: Package System Symptoms: Ambient air temperature: 95°F Return Air Temperature: 81°F Low Side Pressure: 56 psig High Side Pressure: 260 psig Suction Line Temperature: 36°F Liquid Line Temperature: 105°F Evaporator Fan Motor drawing Lower Amps than normal, a light layer of frost on 90% of Evaporator coil
TXV Overfeed
Complaint: Very Little Cooling Type Unit: Package System Symptoms: Ambient air temperature: 101°F Low Side Pressure: 90 psig High Side Pressure: 350 psig Static Pressure: 200 psig Low Sub-Cooling Low Superheat Sweat on Suction Line There are no signs of any restrictions Return Air Temperature: 85°F
Restricted Suction drier
Complaint: Very Little Cooling Type Unit: Package System Symptoms: Ambient air temperature: 105°F Low Side Pressure: 65 psig High Side Pressure: 280 psig Static Pressure: 211 psig Suction Pressure at Suction drier inlet is 70 psig Supply Air Warm Sight Glass Clear Suction Line Warmer than Normal
Shortage of refrigerant
Complaint: Very Little Cooling Type Unit: Package System Symptoms: Ambient air temperature: 95°F Low Side Pressure: 54 psig High Side Pressure: 220 psig Static Pressure: 182 psig Bubbles in the Sight Glass Liquid Line Temperature at the Condenser 106°F Suction Line Temperature at the TXV bulb is 49°F Evaporator has a definite Frost Line at the point of refrigerant saturation
Excessive Heat Load due to Broken return duct
Complaint: Will not Cool Conditioned Space Sufficiently Type Unit: Package System Symptoms: Ambient air temperature: 103°F Low Side Pressure: 80 psig High Side Pressure: 335 psig Static Pressure: 205 psig Conditioned Space Temperature: 85°F High Superheat Supply Air Temperature: 80°F Both Coils and Filter are Clean Return Air Temperature at the Evaporator is 95°F
The main cause of high condensing temperatures and pressures in air cooled condensers is:
Dirty condensers
A system with a loose TEV sensing bulb would most likely:
Have a low superheat
What will be the symptoms of an overcharged unit?
High sub-cooling and low superheat
Evaporator Fan Motor Turning Too Slow
Problem #20 •Complaint: Unit will not cool well Type of Unit: 4 ton Central A/C Unit •Symptoms: Evaporator coil and return air filter are clean. Ambient air temperature is 86°F Discharge pressure is 228 psig Suction pressure is 52 psig Return air temperature entering the evaporator coil is 70°F. Supply air temperature leaving the coil is 44°F.
The most common type of single phase motor found in residential AC systems is:
PSC
Break in Supply Air Duct
Problem #3 •Complaint: Unit runs continuously with poor cooling •Type Unit: Split system with air handler in the garage •Symptoms: Ambient air temperature 95°F Static pressure 182 psig Return air temperature 85°F Low side pressure 76 psig High side pressure 292 psig Supply air temperature 65°F Air temperature at return filter 85°F Temperature at air supply vent 70°F Air velocity is low
Evaporator Fan Speed Too Slow
Problem #4 •Complaint: Runs Too Much •Type Unit: Package System •Symptoms: Ambient air temperature 114°F, Low side pressure 60 psig High side pressure 320 psig Static pressure 240 psig Return air temperature 82°F Supply air temperature 54°F Both coils and filter are clean Superheat is normal
Low Capacity Compressor (Bad Compressor)
Problem #5 •Complaint: Not Cooling •Type Unit: Remote A/C System •Symptoms: Ambient air temperature 105°F Low side pressure 110 psig High side pressure 285 psig Static pressure 210 psig Supply air temperature 79°F Return air temperature 83°F Suction line temperature 68°F
Correct answer: Evaporator Fan Speed Too Slow
Problem #6 •Complaint: Unit cools okay but runs a lot-House air seems very dry •Type unit: Remote with Furnace and Direct Drive Blower •Symptoms: Ambient air temperature 95°F Low side pressure 61 psig High side pressure 252 psig Both coils and filter are clean Return air temperature 82°F Supply air temperature 54°F
Correct answer: Refrigerant Shortage
Problem #7 •Complaint: No Cooling •Symptoms: Ambient air temperature 95°F Low side pressure Low High side pressure Low Evaporator split Low Compressor amp draw is lower than normal High Superheat Low sub-cooling Low condenser split
Correct answer: Overcharged
Problem #8 •Complaint: Lack of Cooling •Symptoms: Suction Pressure High Head Pressure High Compressor Amp Draw High Superheat Low Evaporator split Low Sub-cooling High Condenser split Low
Excessive Heat Load
Problem #9 •Complaint: No Cooling •Symptoms: Suction pressure High Head pressure High Condenser split High Evaporator split Low Sub-cooling Low Superheat High
The cooling cycle
The outdoor coil is the condenser in:
**Correct! all of these answers are correct** increase system capacity insure a solid stream of liquid to the metering device increase system efficiency
The purpose of subcooling the liquid refrigerant is to:
reject heat from the refrigerant
The purpose of the condenser in a refrigeration system is to:
suction line
The refrigerant line whose sizing has the most effect on the compressor's compression ratio is the:
Superheat
Thermostatic expansion valves respond to changes in:
Reduce the airflow over the evaporator
To increase latent cooling capacity:
Why are aluminum fins added to evaporator and condenser coils?
To increase the surface area of the coils
Static pressure readings are taken on a duct system by
Pointing the pressure sensing tube perpendicular to the air stream
If you have an A/C with a low superheat, high sub-cooling, and both PSIGs are high:
You are overcharged
If you have two low pressures and low super heat
You have poor air flow on the evaporator
If you have a dirty condenser:
Your pressures will be high
The total resistance in a series circuit is:
Dependent on the voltage supplied to the circuit
A compressor with a suction pressure of 120 psig and a discharge pressure of 480 psig has a compression ratio of?
(480 + 15) / (120 + 15) = 495 / 135 = 3.67 to 1
45°F + 15°F = 60°F suction line temperature
An air conditioning system charged with R-410A is operating with a suction pressure of 130 psig which equates to a 45°F saturation temperature. If the manufacturer calls for a 15°F superheat, what should the suction line temperature be?
The heat rejected by the condenser:
: Equals the heat absorbed by the evaporator
A technician finds a coil that is frozen with ice. What could be one of the causes?
A dirty air filter
When a technician finds a high split across an evaporator coil this could be an indication of:
A dirty air filter
A reading of 40 degrees subcooling would indicate a:
A high liquid level in the condenser
All HVAC/R equipment is designed to operate satisfactorily on supply voltages of plus or minus:
10%
With a high superheat
A TEV with a dead power element will operate:
(480 + 15) / (120 + 15) = 495 / 135 = 3.67 to 1
A compressor with a suction pressure of 120 psig and a discharge pressure of 480 psig has a compression ratio of?
Removing heat from the room
A mechanical refrigeration system cools a room by:
Low evaporator airflow
A problem that can look like low refrigerant charge if a service technician is only looking at system pressures is:
Experiencing flooding
A system operating with a suction line superheat of 5° or less is probably:
Have a low superheat
A system with a loose TEV sensing bulb would most likely:
It is sub cooled
An air conditioner with refrigerant R-410a has a high side pressure of 340 psig and a temperature of 95°F. According to the pressure temperature chart:
15°F
An R-134a TEV system is operating with a suction pressure of 22 psig and a suction line temperature at the bulb of 40°F. What is the actual operating superheat?
13°F
An R-22 TEV system is operating with a suction pressure of 76 psig and a suction line temperature at the bulb of 58°F. The actual operating superheat is:
It is saturated
An air conditioner using refrigerant R134a has a low side pressure of 35 psig and a temperature of 40°F. According to the pressure temperature chart:
It is superheated
An air conditioner with refrigerant R-22 has a low side pressure of 70 psig and a temperature of 55°F. According to the pressure temperature chart:
In the middle of the evaporator where the cold liquid turns to a cold gas
At what point in the refrigeration cycle does the refrigerant absorb the most heat?
In the middle of the condenser where it changes from a gas to a liquid
At what point in the refrigeration cycle does the refrigerant lose the most heat?
The outdoor coil is the condenser in:
Both the cooling and defrost cycles
Correct Answer Any of these answers Dirty Evaporator Coil Slow Fan, Dirty Fan Wheel Lack of Evaporator Air
Complaint: Cooling not adequate Type Unit: Package System Symptoms: Ambient air temperature: 100°F Low Side Pressure: Low High Side Pressure: Low Static Pressure: 195 psig Return Air Filter Ok High Evaporator Split Low Superheat Heavy Sweating on the Suction Line
Air/Non Condensable
Complaint: Inadequate cooling Type Unit: Package system Symptoms: Ambient air temperature: 100°F Suction pressure: 82 psig Discharge pressure: 335 psig Compressor hotter than normal Compressor Amps Higher than normal Temperature Split across Condenser: High Temperature Split across Evaporator: Low Return Air Temperature: 86°F Supply Air Temperature: 71°F Suction line warmer than normal after shutdown High Side Gauge reads 220 psig
Liquid Line Restriction between Condenser and Sight glass
Complaint: Insufficient Cooling Type Unit: Package System Symptoms: Ambient air temperature: 91°F Low Side Pressure: 62 psig High Side Pressure: 210 psig Static Pressure: 170 psig Compressor Amps Low Compressor Running Hotter than Normal Sub-Cooling is 20°F Supply Air is Warm Liquid Line Temperature at the TXV inlet is 70°F Bubbles in the Sight Glass
Condenser Fan Motor Problems
Complaint: No Cooling Type Unit: Split System Symptoms: Ambient air temperature: 90°F Static Pressure 167 psig Refrigerant Charge Ok Both Coils and Filter Ok Compressor Starts and Runs but Cycles on Overload After 10 minutes of operation the: Low Side Pressure is 84 psig High Side Pressure is 390 psig Liquid Line is Very Hot Bubbles appear in the Sight Glass Occasionally
Compressor has bad valves or blown head gasket
Complaint: No cooling Type Unit: Package system Symptoms: Ambient air temperature: 95°F Static Pressure: 181 psig Both coils and filter are clear Compressor running hot with low Amps Refrigerant charge is ok Suction Pressure: 78 psig Discharge Pressure : 214 psig Compressor Runs Noisy On Unit Shutdown the system pressures equalize quickly
Open Return Duct, Drawing in Hot Air
Complaint: Not Cooling Type Unit: Package System Symptoms: Ambient air temperature: 95°F Static Pressure 182 psig Suction Pressure: 68 --- Drops down into a vacuum Discharge Pressure: 278 psig --- Decreases while Low Side pressure drops into vacuum Sub-cooling: High There are Bubbles in the Sight Glass A Temperature drop can be felt across the Liquid line Drier
Lack of Condenser Air
Complaint: Not Cooling Type Unit: Remote A/C System Symptoms: Ambient air temperature: 105°F Low Side Pressure: 110 psig High Side Pressure: 285 psig Static Pressure: 210 psig Supply Air Temperature: 79°F Return Air Temperature 83°F Suction Line Temperature 68°F
Air/Non Condensable
Complaint: Not Cooling Well Type Unit: Package System Symptoms: Ambient air temperature: 95°F Low Side Pressure: High High Side Pressure: High Sight Glass Shows Occasional Bubbles Liquid Line warmer than Normal Compressor running Hotter than Normal Suction Line Warmer than Normal On Shutdown the Static Pressure does not correspond to Ambient Temperature
Severe Undercharge
Complaint: Not Cooling at all Type Unit: Package System Symptoms: Ambient air temperature: 95°F Low Side Pressure: 40 psig High Side Pressure: 205 psig Static Pressure: 184 psig Compressor Hot with Low Amps High Superheat Liquid Line Warmer than Normal Spitting Noise can be Heard at the TXV
Undercharge
Complaint: Not cooling well Type Unit: Package system Symptoms: Ambient air temperature: 110°F Compressor Running Hotter than Normal Bubbles in the Sight Glass Compressor Amps Lower than Normal Suction Line Temperature: 50°F Liquid Line Temperature: 126°F Low Side Pressure: 60 psig High Side Pressure : 290 psig
Evaporator Fan Speed too Slow
Complaint: Runs Too Much Type Unit: Package System Symptoms: Ambient air temperature: 114°F Low Side Pressure: 60 psig High Side Pressure: 320 psig Static Pressure: 240 psig Return Air Temperature: 82°F Supply Air Temperature: 54°F Both Coils and Filter are Clean Superheat is Normal
Dirty Evaporator Coil
Complaint: Unit Cools Okay but Humidity is too Low Type Unit: Package System Symptoms: Ambient air temperature: 111°F Low Side Pressure: 62 psig High Side Pressure: 334 psig Static Pressure: 230 psig Suction Line Temperature: 42°F Liquid Line Temperature 132°F Return Air Temperature 80°F Supply Air Temperature 55°F Return Air Filter is Clean
Break in Supply Air Duct
Complaint: Unit Runs Continuously with poor cooling Type Unit: Split System with Air Handler in the Garage Symptoms: Ambient air temperature: 95°F Static Pressure: 182 psig Return Air Temperature: 85°F Low Side Pressure: 86 psig High Side Pressure: 292 psig Supply Air Temperature: 65°F Air Temperature at Return Filter: 85°F Temperature at Air Supply Vent: 70°F Air Velocity is Low
The fan motor current draw will decrease
If the air inlet to a centrifugal fan is restricted:
The purpose of subcooling the liquid refrigerant is to:
Increase system capacity
What type of furnace will have a negative pressure inside the heat exchanger
Induced draft
The low side manifold gauge is called a compound gauge because:
It reads low side pressure and vacuum
If a package unit has a blower belt slipping, what kind of superheat would you expect?
Low superheat
Lowering liquid refrigerant temperature below its saturation temperature
Lowering refrigerant temperature by flashing some of it off to a gas, cooling the remaining liquid
Thermostatic Expansion Valves are designed to:
Maintain a constant superheat in the evaporator coil
On a heat pump thermostat, if the jumper between the W and Y terminal is open, how will it affect the system?
No Heating
The two types of transformers used in HVAC systems are:
Step-down and Step-up
When a liquid is cooled below its boiling, or saturation point it is called
Sub-Cooled Liquid
The difference between the condenser saturation temperature and the liquid line temperature is defined as:
Subcooling
When gas is heated above its boiling, or saturation point, it is called
Superheated Gas
What is the free area of a register or grille?
The amount of the grille face area that is open
Relays and contactors have the same function except
The contactor carries more current than the relay
Equals the heat absorbed by the evaporator plus the heat added by the compressor
The heat rejected by the condenser:
The heating cycle
The indoor coil is the condenser in:
Dirty condensers
The main cause of high condensing temperature and pressure in air cooled condensers is:
Low airflow caused by dirty or plugged air filters
The most common airflow problem experienced on air conditioning systems is:
A capacitor is rated by its capacity in Micro Farads and:
Voltage Limit
The reversing valve
What component is responsible for reversing the flow of refrigerant in a heat pump?
The amount of the grille face area that is open
What is the free area of a register or grille?
1200 CFM (400 PER TON X 3 TONS )
What is the standard airflow across the evaporator of a 3 ton residential split system air conditioner?
**ALL of these answers are correct** a dirty indoor air filter a restricted liquid line filter drier an underfeeding metering device
Which of the following conditions would likely decrease the suction pressure?
A TEV with a dead power element will operate:
With a high superheat
An open circuit is a circuit:
Without a complete path
