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Because HVAC work varies over the course of the year, we have divided our catalog into two distinct seasons: Spring/Summer and Fall/Winter. This division helps service techs and maintenance personnel to select the proper test equipment for each time of the year. The HVAC AC category includes testers used to troubleshoot problems in AC cooling units, circuits and ventilation systems, as well as find other issues in the refrigeration field.
The most common testers used for AC cooling and refrigeration include: AC manifold gauge sets, vacuum pumps, refrigerant recovery machines, refrigerant scales, leak detectors (both dye type and sensor based), AC charging hoses, electronic micron vacuum gauges, HVAC multimeters and clamp meters, recovery tanks, air velocity meters and CFM anemometers, and various types of thermometers.
What are the newest techniques and innovations in test equipment?
HVAC AC Service Technicians now most often use digital manifold gauge sets as they provide more accurate readings and the ability to use the same piece of equipment for all refrigerants. They also use IR thermometers and thermal cameras to scan AC units for problems that are detected by temperature variations of various pieces of equipment. Techs also want to get more mobility and reporting features, so wireless or Bluetooth based testers are becoming a new trend.
Value Testers, as an authorized distributor of many quality brands, keeps up with these innovations in order to offer our clients the best and most cutting-edge test equipment. Our customer service techs receive training from manufacturers that we represent in order to help clients choose the best testers to meet their diagnostic needs. Please call us, and we will help you find best testers and save the most money on your purchase.
AC Cooling System
How AC Systems Work Internally
AC systems cool the air inside an enclosed space (e.g. vehicle or building) by essentially pumping heat from the air inside that space to the air outside of it. “Pumping” is an apt word since the vapor compression cycle which AC is based on has a compressor at its heart.
Inside an AC unit is a closed loop of circulating gas (the refrigerant) which undergoes a phase change from liquid to gas and then back again to liquid. These two phase changes occur in different sections of the AC system: the “high-pressure side” and the “low-pressure side”.
Let’s start with the high-pressure side, which begins at the outlet of the compressor. The compressor’s job is to draw in low pressure gas and squeeze it so that it exits at a higher pressure. When the volume is held constant, compressing a gas increases its temperature. Thus, the high-pressure side of the compressor produces hot (well above the outside ambient temperature) refrigerant under high pressure.
Upon leaving the compressor, the refrigerant then enters the condenser, which is the heat exchanger which transfers heat from the compressed refrigerant to air drawn in from outside and blown across the condenser.
The refrigerant then cools down as it travels through the long tubing of the condenser, until the gas reaches the boiling point for the pressure it’s under. This causes some of the refrigerant to change from gas to liquid, releasing heat (latent heat).
Under ideal conditions, the refrigerant becomes entirely liquid as it exits the condenser and enters the metering device (either a capillary tube or a TXV) which restricts (throttles) the transfer of the liquid refrigerant into the low-pressure side, where the cooling actually occurs.
The metering device is the second device which maintains the separation between the high-pressure and low-pressure sides. By creating a significant flow restriction, a large pressure drop is developed across the metering device.
The liquid refrigerant travels through the metering device and into another large heat exchanger: the evaporator. The pressure inside the evaporator is much lower than in condenser, and as a result, the refrigerant’s boiling point is too. This causes the liquid refrigerant transition from liquid to gas, absorbing the latent heat of vaporization it previously released in the condenser.
This evaporation cools the refrigerant as well as the tubing and fins of the evaporator. Air from the space to be cooled is blown across the evaporator, and thus that air gets cooled. As the liquid refrigerant travels through the evaporator, more and more of it becomes gas until (ideally) all of the refrigerant leaving the condenser is in the vapor (gaseous) phase.
The refrigerant gas is at will be relatively “cool” and at low pressure when it gets drawn into the inlet (low-pressure port) of the compressor, where it is compressed (and therefore heated) and the cycle begins again.
Cooling the Inside Air: Ducts and Grilles
Using the process described above, AC units remove heat from the evaporator and transfer it to the condenser. At the condenser, that heat is transferred again to the outside air by blowing that air via a fan over the tubing and fins of the condenser. The now warmer ambient air disperses into the atmosphere, and is (practically speaking) the end of the story for the hot side of the AC system.
The cold side of the AC system, however, extends far beyond the evaporator. A fan circulates air from the space to be cooled through the evaporator and throughout that space by way ducts and registers (also called grilles or vents).
These ducts and grilles accomplish three main purposes:
1. Pull in warm air to the AC unit’s evaporator
2. Return the cooled air
3. Accomplish both #1 and #2 while keeping the temperatures and pressures of all areas of the inside space balanced.
The ducts and grilles must be appropriately sized and placed to deliver the air flow necessary for uniform and optimal cooling. Just as degrees and psi units are employed to quantify the temperatures and pressures respectively inside an AC system, cubic feet per minute (CFM) is used to specify the air flow capacity of the AC registers and grilles.
The registers through which the cooled air returns often feature adjustable vanes which can both restrict and direct the flow of the cooled air in that particular area of the house.
AC System Controls
For residential AC systems, the main control device is the thermostat. Thermostats measure the air temperature and electrically switch the AC to cool the air if that air temperature is above an adjustable set point, or switch it off if the temperature is below that set point.
In reality, a degree or two of hysteresis is added so that the AC unit isn’t constantly being turned on and off. By waiting not beginning cooling until the air temperature is one or two degrees above the set point (and conversely, not turning off the cooling until the ambient temperature drops a degree or two below the set point), the AC system and all of its components are spared excessive on-off cycling, extending their useful lifetimes.
Many thermostats now use electronic components for both the sensing the switching. They use some kind of temperature sensitive electronic component to feed an analog voltage signal to a chip which translates that signal into a number for comparison against the stored target temperature.
Originally, thermostats used relied on a bimetallic strip whose bend radius depended on the ambient air temperature. This strip is then used as one of the contacts for the switch which turned the AC unit either on or off. These older mechanical/electrical hybrid devices can still be found at work in houses today.
WiFi-enabled home AC thermostats are now on the market which can connect to the Internet via the home’s wireless network. This allows users to monitor and control their home’s temperature through their smartphone or tablet. For instance, someone who bumps up their thermostat during the summer while they’re away at work in order to save energy may choose to begin cooling their home before they even leave the office to ensure that their house is cool and comfortable the moment they walk in.
Split AC systems: What They Are and When to Use Them
What’s a Split AC System?
The AC cooling cycle described above is commonly implemented as a single self-contained unit—a large box which either hangs out of a window or is installed on top of a roof or on the ground next to a house or other building. In these AC units, both the high- and low-pressure parts of the cycle (are their respective components) are housed with the same physical box.
It is also possible, however, to physically separate those halves of the cycle: one unit containing the compressor and condenser (and its blower) while another unit houses the evaporator and cold side vent and blower. The unit containing the evaporator is installed inside, and the unit containing the condenser is usually located outside. The sections are joined by conduit containing tubing for moving the refrigerant to and from the outside unit to the inside one.
AC cooling systems which are separated in this way are referred to as “split” AC systems, in contrast to the “packaged” AC systems which contain both cycles in one unit.
It’s important to note that split AC systems don’t use ducts, due to the fact that more than one inside unit can be connected to a single outside unit, and thus each room can be cooled with ducts and grilles circulating air through the evaporator.
Advantages of a Split AC System
There are two main advantages to using a split AC system over a packaged one:
1. Higher design efficiency: Since the high temperature and pressure part of the cycle is separated from the low temperature and pressure side, and also since split AC systems don’t use metal ducts which can leak heat into the transported air, split AC systems can operate at very high energy efficiencies. SEER values for split systems can range from the 20’s to above 30.
2. Quieter operation: with no large blower needed to push cooled air through a maze of ductwork, split AC systems are often quieter than packaged AC systems of the same cooling capacity.
When to Use a Split AC System
Even though split AC systems have advantages over packaged units, it’s seldom cost effective or practical to switch a building from a packaged AC system to split AC units. This is mostly due to the costs of installing split AC units exceeding those of simply replacing one packaged unit with another one.
The logic of course cuts both ways. Installing ductwork in a house where none previously existed adds considerably to the cost of installing a packaged AC system. This is why it’s recommended by AC pros to continue to use the same type of AC system that was previously used when replacing units.
Other than that general advice, there are a couple of situations when a split system should be utilized:
• If the building or section of the building to be cooled currently lacks ductwork, and installing it isn’t feasible.
• If the area to be cooled is a small apartment or room addition, and extending the existing ductwork to that area isn’t practical.
Split AC systems can be a very efficient and practical AC solution for many buildings.