Flashcards in HVAC II 29, 40 Quiz Deck (29)
What is the first thing a technician should do before beginning troubleshooting?
Know the typical operating conditions of the system, and observe the entire system
What is the coil to air temp relationship for a refrigeration system designed for minimum food dehydration?
8-12 degrees F
What is the evap coil to air relationship when the compressor is not running?
The coil warms, increasing pressure on the low side of the system and eventually matches the box temp
What is meant by the term "Approach" when dealing with evap chilling water?
Delta T between evap coil and cooling water leaving temp (Departure). Heat given to evap
How does a TXV system respond to an overcharged refrigeration condition?
High head pressure and maybe high suction pressure, because superheat is down so valve will not fully open and will eventually close
How does a capillary tube system respond to an overcharged refrigeration condition?
Higher head pressure. Will meter more refrigerant, because head pressure is higher, flooding the evap
How does a TXV system respond to an undercharged refrigeration condition?
May hiss as a partial vapor/liquid mix goes through the valve. Valve will open fully, as superheat is constantly high
How does a capillary tube system respond to an undercharged refrigeration condition?
Less refrigerant is metered through due to low head pressure
What is the compressor's job in an AC system?
To lower the evap boiling temp (through suction) to proper low level
How is Head Pressure calculated?
Ambient temp + Condense temp above ambient (usu. 30) = Head Temp
What is the gpm flowrate for waste water and cooling tower unit?
1.5gpm waste water, 3 gpm cooling tower
What is the standard water temp increase across the condenser in cooling tower system?
10 degrees F
What are six typical problems in an AC system?
1. Low refrig charge. 2. Overcharge. 3. Inefficient Evap. 4. Inefficient Condenser. 5. Restriction in refrig circuit. 6. Inefficient Compressor
The standard design conditions for AC systems established by the ARI are outside temp____ degrees F, inside temp____ degrees F, with a humidity of____%.
95, 80, 50
The typical temp relationship between a standard-efficiency air-cooled condenser and the ambient temp is.
30 degrees F
The evap will normally operate at a ____ degree F boiling temp when operating at the 75 degree indoor temp with a 50% humidity condition.
40 degrees F
A typical temp relationship between a high efficiency condenser and the ambient temp is:
20 degrees F
How is the condenser high efficiency obtained?
Usually oversizing condenser, evap, and new alloys for heat exchangers
What type of metering device is typical for high-efficiency systems?
TXV, sometimes fixed-bore
What does the head pressure do if the suction pressure rises?
What will cause the suction pressure to rise?
Higher indoor evap load, as from unit off for extended period
The evap design temp may in some cases operate at a slightly higher or lower pressure and temp on high-efficiency equipment because the evap is larger.
Slightly higher. Absorbing more heat
The seasonal energy efficiency ratio (SEER) includes the energy used in the ____ and ____ cycles.
Start up and shutdown
The electrical operating conditions are measured with a ____ and ____
Voltmeter and Ammeter
The three major power-consuming devices on an AC system that may have to be analyzed are:
Indoor fan motor, outdoor fan motor, and the compressor
AC systems normally move about ____ cfm of air per ton.
400 cfm per ton
The compressor amperage of a 3-ton system operating on 230VAC is approximately ___A.
Many ratings for components of an AC system are not completely accurate due to many different operating conditions that are called ___ ratings.