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garfigator
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-
- author "me"
- tags "Cooling 101"
- description ""
- fileName "Cooling terms"
- freezingBlueDBID -1.0
- Air conditioner
Device used to control temperature, humidity, cleanliness and movement of air in a conditioned space.
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*** is oversize better?
No, b/c uncompotable, humidity control problem, system will be on/off too often.
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Ambient temperature
Temperature of fluid (usually air) which surrounds on object on all sides.
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Back pressure
- Pressure on low side of the refrigerant system;
- Also, called the suction pressure or low side pressure.
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British Thermal Unit (BTU)
Quantity of heat requires to raise the temperature of one pound of water one degree fahrenheit in one hour.
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Change of state
Condition in which a substance change from a solid to a liquid or a liquid to a gas due to addition of heat. Or the reverse, in which a substance change from a gas to a liquid or a liquid to a solid due to the removal of heat.
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Cold
- - The absence of heat;
- - A temperature considerably below normal.
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Compressor
Pump of a refrigeranting mechanism which draws a low pressure on cooling side of the refrigerant cycle and squeezes or compresses the gas into high-pressure on the condensing side of the cycle.
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Condenser
The part of the refrigeration mechanism which receives high pressure, high temperature gas from the compressor and cools gasous refrigerant until it returns to a liquid state.
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Evaporator
Part of the refrigerating mechanism in which the refrigerant vaporizes and absorbs heat.
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Flooding
Act of allowing a liquid to flow into a part of a system.
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Head pressure
Pressure which exists in condensing side of refrigerating system. Also, called in Discharged or High side pressure.
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Heat
- - Form of energy
- - Energy associated with random motion of molecules.
- - It cannot be created or destroyed, but can be transferred from one substance to another.
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Latent Heat
Heat added or removed from substance to change its state without changing its temperature. Also, called Hidden Heat.
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Metering device
Device used to regulate the flow of liquid refrigerant into the evaporator. It can be a capillary tube, expansion valve, or a piston.
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Saturation
- - Condition existing when a substance contains all another substance it can hold.
- Ex) sponge
- - presence of both liquid and vapor at any given temperature.
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Saturated vapors
Vapor condition which will result into droplet of liquid if the vapor temperature is reduced lower than saturation.
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Sensible heat
- - Heat which causes a change in temperature of a substance.
- Ex) 32°F - 212°F. ; 180BTU
- - Measurement of intensity ( also definition of temperature).
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Subcooling
Cooling of a liquid refrigerant below its condensing temperature.
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Superheat
- - Heat added to a vapor above its boiling temperature or saturation temperature.
- - temperature difference between the boiling temperature of a liquid and the vapor temperature.
- - the difference between the temperature at the evaporator outlet and the temperature of the refrigerant in the evaporator.
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Ton of refrigeration
- - Refrigerating effects equial to the melting of one-ton of ice in a 24-hour period.
- Ex)
- 288,000 btu's/24 hr.
- 12,000 btu's/1 hr.
- 200 btu's/per min.
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Vacuum
- - pressure lower than atmosphere
- - atmospheric pressure = 14.7 psi
- - vacuum allows moisture to boil at lower temperature.
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Heat flows in three ways
- Conduction
- Convection
- Radiation
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Conduction
- Is the transfer of heat from molecule to molecule through a substance by chain collision.
- Ex)
- In natural,
- In a space as cooling load,
- In equipment as cooling capacity.
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Convection
The movement of heat from one place to another. Place by way of fluid or air.
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Heat transfer by convection
Free convection and forced convection.
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Radiation
- Transfer heat by passing from a source to an absorbent surface without heating the space in between.
- - the transfer of heat by rays.
- Ex)
- Sun,
- Lamp,
- Fireplace,
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Heat transfer
Movement of heat from one body or substance to another. Heat may be transferred by radiation, conduction, convection or a combination of these methods.
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What is refrigeration
Is cooling by the removal of heat.
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Movement of heat
Refrigeration is the transfer of heat from where it is not wanted to a place where it is not objectionable.
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Note 30:
- - Temperature indicates the average velocity of the molecules of a substance.
- - Temperature does not measure the spacing and arrangement of molecules within a substance.
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Refrigerant
- - any fluid or gas used as a medium to transfer heat.
- - has a pressure temperature relationship.
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The mover of heat
A refrigerant is a fluid that picks up heat by evaporating at a low temperature and pressure and rejects heat by condensing at a higher temperature and pressure.
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Note33:
Total heat is equal to sensible plus latent heat.
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Pressure
- - energy impact on a unit area.
- - force or thrust on a surface.
- Ex)
- Top of atmosphere
- 14.7 psi @ sea level then
- The 1 sq.in. air = 14.7 lbs.
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Latent heat of vaporization for water
970 BTU/HR PER LB.
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Latent heat of fusion for water; ice 32° to water
144 BTU/HR PER LB.
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Specific heat
The amount of heat, measured in BTU's, requires to raise one pound of a substance one degree fahrenheit.
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Note: specific heat
- One pound of dry air = 13.3 cu.ft.
- 0.24 BTU/HR to raise 1 lb. of air 1°F
- 1 lb. x 0.24 (specific heat) x 60 min. = 14.4 specific heat per hour
- (14.4 specific heat/hour) / (13.3 cu.ft.) = 1.08 specific heat of 1CFM of air
- 1 ton = 2000 lb.
- 1 gal. = 8.34 lb.
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Compound gauge
- Blue side,
- Low side,
- Measurng pressure & vacuum
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Accumulator
Storage tank that receives liquid refrigerant from the evaporator and prevents it from flowing into the suction inlet of the compressor.
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Capacitor
Property of a nonconductor that permits storage of electrical energy.
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Circuit breaker
A device that is a switch and a safety that automatically opens an electrical circuit if overload or short circuit arises.
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Cankcase heater
Def. = prevents liquid migration in the off cycle.
- Device installed around the base or sump or the compressor.
- Adds heat to the compressor to keep the refrigerant in a vapor state to prevent slugging on start up.
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Compressor ratio
- Ratio of the volume f the clearance space to the total volume of the cylinder.
- In refrigeration it is also used as the ratio of the absolute low-side pressure to the absolute high-side pressure.
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Condensate
A fluid formed when a gas is cooled to its liquid state.
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Condensation
Liquid or droplets that form when a gas or vapor is cooled below its dew point.
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Condensate pump
Device used to remove water condensate that collects beneath an evaporator.
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Cut-in
The temp. or pressure at which he control circuit closes.
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Cut-out
The temp. or pressure at which the control circuit opens.
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Dew point
Temp. at which vapor (@ 100% humidity) begins to condense and deposit liquid.
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Drier
- A device used to remove moisture and debris from a refrigeration system.
- Made up of filtering screens and activated alumina used as the drying agent or dessiccant.
- Drier needs to be replaced every tme you open up the system.
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Dry bulb temperature
Air temp. as indicated by an ordinary thermometer.
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Ground short
Fault in an electrical circuit allowing electricity to flow into the metal parts of a mechanism.
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High pressure switch (R-22)
- Electrical control switch, mounted on the discharge or liquid line after the condenser coil (within he unit).
- normally closed-opens on a pressure rise.
- Opens @ approx. 400 PSIG ~ 450 PSIG.
- Automatic reset.
- Closes @ approx. 300 PSIG.
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Humidity
Moisture or dampness of air.
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Locked rotor current
- Initial current when initially closing a circuit, normally atleast 3 to 4 times greater then the running amperage.
- Measured on the common leg of the compressor from a cold start with equalized pressure.
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Low pressure switch (R-22)
- A switch located in the suction line/side or low side of the cmpressor that will de-energize the contactor during a low pressure condition.
- Normally open switch
- Opens @ approx. 25 PSIG.
- Closes @ approx. 50 PSIG.
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PTCR / PTC = positive temperature coefficient resistor
- A thermistor installed in parellel with the run capacitor and in series with the start winding.
- Allow current to flow to the start winding until the PTC heats up to 260° F.
- Must have a time delay installed with.
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Overload protector
Device embedded within a motor winding to shut the motor off should either the component develop a excessive temperature situation or intense heat via excessive current.
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Permanent split capacitor motor
A motor with no relay in which current flows through boh the starting and running winding, making the motor sensitive to line voltage and resulting in low starting torque.
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Potential relay
- Electrical relay that opens its normally closed contacts on an increase of BEMF from a motor and reclose contacts when the voltage drop.
- Wired in parellel with the start winding.
- Uses a starting capacitor to boost compressor starting torque.
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Psychrometer
Device used for measuring relative humidity and wet bulb temp.
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Relative humidity
Ratio of the difference between the amount of water vapor present in air to the greatest amount possible at the same temp.
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Relay
- An electromegnetic mechanism used to operate a switch to control a device.
- Relay under 20 amps - general purpose.
- Relay over 20 amps - are called contactor.
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Run winding (main windng)
Electrical winding of a motor that has current flowing through it during normal operation.
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SEER (seasonal energy efficiency ratio)
The ratio of rated cooling capacity divided by the amount of electrical power used in watts during a season of operation.
- E.E.R. = the same ratio but at full load condition.
- Ex) 36,000 BTUdivided by 4000 watts = 9.0 S.E.E.R.
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Starting capacitor
- Capacitor used soley for increasing the starting torque of electric motor.
- Wired in series with the start winding and is controlled by the BEMF of a motor on start up and drop out when the motor reaches 75% of its BEMF.
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Start winding
Winding in electric motor used mainly for starting the electric motor.
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Time delay fuse
- A fuse that does not blow until the overload has persisted for a set duration of time.
- Normally about 10 seconds.
- Ignores the initial current surge or locked rotor current on a start up situation.
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Time delay relay
- Usually a solid-state device wired in series with the contactor coil and after any pressure or temp. safties that will allow the compressor to start under the least amount of load.
- Normally set @ 5 min.
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Wet bulb temperature
Temperature indication of the rate of evaporation of moisture in an air sample.
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Recovery
The removal of refrigerant from a system.
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Steps for checking suction superheat
- 1. Put low side gauge on the low side of the system to read pressure
- 2. Find the corresponding saturation temp.
- 3. Put a temp. Probe on the suction line to measure temp.
- 4. Subtract the saturation temp. from the measured line temp. to find the amount of superheat.
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Steps for checking subcooling
- 1. Put high side gauge on the high side of the system to read pressure
- 2. Find the corresponding saturation temp.
- 3. Put a temp. Probe on the liquid line to measure temp.
- 4. Subtract the liquid line temp. from the saturation temp. to find the amount of subcooling.
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Methods of charging refrigerant systems
- Weighing method,
- Superheat method,
- Subcooling method,
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Superheat method
Utilized any fixed orifice type metering device.
- There are two ways to charge a system using the superheat method:
- 1) using dry bulb return air temp.
- 2) using wet bulb return air temp.
- ** The wet bulb return air temp. method is the most accurate.
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Subcooling method
Used on equipment utilizing TXV type metering device.
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Note: charging
- Add charge to lower superheat.
- Remove charge to raise superheat.
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The boiling temp. of a liquid is affected by
Pressure
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Why suction is insulated?
- Prevent from condensate.
- Prevent from ambient heat absolve along the suction line.
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Five different states of the refrig. in order between the discharge line to the liquid line.
- (Discharge line)
- Hi pressure/temp ; superheat vapor
- (Condenser coil)
- Hi pressure/temp ; saturated vapor/liquid
- (Liquid line)
- Hi pressure/temp ; sub cooled liquid
- (Evaporator coil)
- Lo pressure/temp ; saturated liquid/vapor
- (Suction line)
- Lo pressure/temp ; superheat vapor
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Four major components of the refrigerant cycle
- Compressor
- Condenser
- Metering device
- Evaporator
Only the size, style and arrangement of the four basic refrigerant components will change from system to system.
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Compressor (functions)
- Maintains a pressure differential between inlet(suction) and its outlet(discharge) that will cause refrig. to flow in sufficient quantities to meet coling requirements of the system.
- The function of a compressor is to take refrigerant vapor at low temp. and pressure and raise to a higher temp. and pressure.
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Compressor types
- Rotary
- Reciprocating
- Centrigugal
- Screw
- scroll
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Excessive liquids in compressor
- High power usage
- Motor overheating
- Compressor overheating
- Oil breakdown
- Improper compressor lubrication
- Noisy operation
- Vibration
- Compressor damage through deformity and breakage
- Inadequate capacity
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Condenser (function)
- Changes high pressure, high temp. vapor discharged from the compressor to a high pressure sub cooled liquid.
- Rejects heat that was absorbed in system.
- The condenser is a device for removing heat from the refrigeration system.
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Types of condensers
- Air cooled
- Water cooled
- Evaporative
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Sub cooling
- Sub cooling increases system efficiency & capacity by 1/2 % per degree.
- Insures full column of liquid entering the metering device.
- Ex) 3 ton A/C = 36000 BTU/HR
- requires sub cooling = 15 degrees
- System that only has 1 degree of subcooling has a capacity loss of 2520 BTU/HR or 7%.
- Capacity reduced to 33480 BTU/HR
- ex) 4 ton A/C
- Requires subcooling 14 degree
- Actual subcooling 2 degree
- 14 - 2 =12
- 12 / (1/2 %) = 6% capacity loss
- 4 x 12000 = 48000
- 48000 x 6% = 2880 loss
- 48000 - 2880 = 45120 BTY/HR
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Sub cooling coil
- Cools liquid refrigerant below its saturation temperature.
- Dirty condenser is number one cause of compressor failure.
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Dirty condenser coils
- A dirty condenser restricts the ability to reject heat causing excessive head pressure and compressor temp.
- Excessive compressor temp. will cause the lubricating oil to break down, create sludge in oil, and acid formation can occur.
- Dirty condenser coils cause higher discharge pressure which causes higher compressor amperage which increases operating costs and reduces system capacity.
- This problem is greatly intensified when the outdoor ambient temp. is high.
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Metering device ( function)
- Maintain an evaporator pressure that will result in a saturated vapor temp. in the evaporator below the entering air temp. so heat can be transferred from the air to the refrigerant.
- - meters refrigerant into the evaporator
- - provides a pressure drop which saparates the high side from the low side of the system.
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Two types of metering devices
- Fixed type
- - capillary tube
- - fixed orifice
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Adjustable type of metering devices
- Hand expansion valve (F)
- Lowside float valve
- Highside float valve
- Automatic expansion valve
- Thermostatic expansion valve
- Electric / Electronc expansion valve
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Capillary tube design complications
- Too long and too small in diameter = starved evaporator
- Too short and too large in diameter = evaporator flooding
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Capillary tube application
- Well suited for:
- - fairly constant load
- - Small capacity
- - less than equil 3 tons
- - residential comfort
- - household refrigeration
- - factory design
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Poorly suited for capillary tube:
- - widely changing loads
- - large capacity
- - greater than 10 tons
- - commercial comfort
- - commercial / industrial refrigeration
- - field design
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Metering device assembly
Body > piston (orifice) > retainer > flare nut
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Thermostatic expansion valve (TXV)
A txv maintains a constant superheat of 10 degrees by modulating a needle valve allowing more or less refrigerant flow depending on the operating forces of the txv.
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The three operating pressures of a txv are:
- Spring pressure
- Back(suction) pressure
- Bulb pressure
- Spring and back pressure tries to open the valve allowing more refrigerant to flow through the evaporator.
- Most txvs are hard shut off which means the pressures do not fully equalize on the off cycle. (For higher efficiency)
- For this reason if you are replacing an indoor coil with a fixed orifice with a coil that has a txv (all new indoor coils), compressor, a hard start must be installed.
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Valve closing - superheat too low
E + S > B
Valve opening - superheat too high
E + S < B
Compressor will not start till the pressures are equalized.
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To measure superheat
- Find suction pressure
- Find matching saturation temp.
- Read temp. leaving evaporator.
- Superheat = temp. leaving - saturation temp.
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Common metering device problem
- Stuck expansion valve
- Oversized expansion valve
- Improper sensing bulb location
- Valve superheat setting too low or too high
- Wrong type valve
- plugged equalizer line
- Plugged distributor
- Improperly sized distributor nozzle
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Evaporator (function)
- Transfers heat from entering air to the refrigerant in the evaporator.
- Absorbs heat into system
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Common evaporator problems
- Inadequate air flow through the coil
- Uneven air distribution over coil
- Inadequate refrigerant supply to coil
- Uneven refrigerant distribution to coil circuits.
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Condensate pump in A/C inspection: 3 things need to be done
- Make sure safety switch is wired in.
- Take apart and clean condensate pump.
- Fill it up with water and make sure it works.
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B&B water damage policy
- Attic air handlers, condensing furnaces, & horizontal coils will be hung as high as possible, suspended with heavy solid link chain & properly supported b uni-strust their entire length.
- We want as much pitch on the drain as possible.
- Coils installed in the upflow position must have an E-Z Tee installed in the high drain port.
- Air handlers installed in the upflow position will have an E-Z Trap and E-Z Tee installed.
- All condensate pumps must have a safety switch and it must be wired in to the control circuit.
Without prior permission from the homeowner, No water valves shall be turned ON/OFF (i.e. outdoor spigots, main water to water heater / home etc.)
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Attic installations
- May have to offset the plenums for proper pitch. ( quote accordingly)
- Install a properly supported emergency drain pan (minimum depth 4" deep and tested for water leakage.) With separate drain line and pitched towards the drain.
- Emergency pan safety float switch to be installed.
- Primary drain will have an E-Z trap.
- The high drain will be piped into the emergency drain pan or have an E-Z Tee installed.
- All safeties are to be wired in series and shut down the system should a malfuction occur.
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Existing installations
- On existing installations, we will automatically recommend the appropriate safety devices.
- Be sure to note on the ticket if the customer does not want them installed.
- the service ticket Should have the following statement:
- " customer refused water safeties. No guarantee on drainage. B&B is not responsible for water leak damages."
- Existing installations utilizing a free draining humidifier and a condensate pump must have a safety switch on the condensate pump.
- The safety switch shall be wired to break "R" power to the thermostat.
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Humidifiers
- Free draining humidifiers are not to be installed on condensate pumps.
- A gravity type drainage system must be available (i.e. floor drain or gravity drain to slop sink.)
- When no gravity drain is available install a circulating / wicking type humidifier.
- Humidifiers are not to be installed in attic or spaces exposed to temp. below freezing under any cicumstances.
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Humidifier overflow drain
Any humidifier equipped with any overflow drain must have the overflow drain piped to the nearest drain system, (i.e. A/C drain, condensate pump, etc.) as a safety.
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