What is a sensing bulb?
What is a sensing bulb?
A sensing bulb is a bulb filled with a gas whose volume changes with temperature. When the temperature crosses some limit, the expanded gas triggers a valve. This is used frequently in air conditioning systems: figure below.
Where is the sensing bulb located?
The sensing bulb needs to be mounted on a horizontal section of the suction line in the 3-o’clock or 9-clock position. Insulate the sensing bulb thoroughly so that it receives a good temperature signal from the gas in the sensing bulb.
What is inside the sensing bulb?
The bulb is filled with a refrigerant which is kept completely separate to the refrigerant in the rest of the system, these two refrigerants never meet or mix they’re always separated. The superheat boils the refrigerant inside the bulb and as it boils it creates pressure.
How does a TEV work?
The TEV strives to maintain a stable level of superheating inside the evaporator under all conditions by adjusting the mass flow of refrigerant in response Into the evaporator load. This is achieved by a membrane inside the valve housing, which compares the temperature before and after the evaporator.
How do you install a sensing bulb?
The sensing bulb should be attached at 12 o’clock on any suction line of 7/8-inch diameter or smaller. On lines larger than 7/8-inch diameter, the bulb should be placed at either 4 or 8 o’clock. The bulb should never be placed at 6 o’clock. Always insulate the entire sensing bulb after installation.
How do you test a sensing bulb?
Check the evaporator coil and remove the TXV’s sensing bulb from the suction line. Check the subcooling, superheat and pressures again. If there’s no change, that’s a further indication of a TXV problem. Another test is to put the sensing bulb in ice water and checking the pressures superheat, and subcooling again.
Can a sensing bulb be vertical?
A sensing bulb can be installed on a vertical suction line if necessary, but never place the bulb downstream of a trap. Bulb placement before a trap (upstream) is recommended. Remember, with R-410A, traps are no longer necessary. When putting the bulb on a vertical line — always — TAIL END UP!
What is a thermostat sensing bulb?
Bulb and capillary thermostats have a fluid filled bulb and respond quickly to change in temperature. These temperature sensors are used in a variety of applications as temperature and regulating devices or high limit safety sensors.
What are the two types of TEV designs?
There are two main types of thermal expansion valves: internally or externally equalized. The difference between externally and internally equalized valves is how the evaporator pressure affects the position of the needle.
What is receiver drier?
The receiver drier is a component that protects all the other parts of the A/C loop. It is located between the condenser outlet and the expansion valve inlet, on the high pressure side of the circuit.
What is a sensing bulb used for?
A sensing bulb is a bulb filled with a gas whose volume changes with temperature. When the temperature crosses some limit, the expanded gas triggers a valve. This is used frequently in air conditioning systems: figure below.
What causes the pressure inside the sensing bulb to increase?
Because the sensing bulb is in direct contact with the pipe of the evaporator outlet, the thermal energy transfers and causes the refrigerant inside the sensing bulb to expand and boil. As the refrigerant expands and boils it causes the pressure inside to increase.
What is the function of the sensing bulb in an evaporator?
The sensing bulb sits at the outlet of the evaporator. As a result, the cooling load of the evaporator increases the superheat increases at the evaporator outlet. Because the sensing bulb is in direct contact with the pipe of the evaporator outlet, the thermal energy transfers and causes the refrigerant inside the sensing bulb to expand and boil.
What happens if the sensing bulb is not installed correctly?
An incorrectly installed or placed sensing bulb can lead to two major system problems: Refrigerant flooding back to the compressor, or the evaporator being starved for refrigerant and not operating at its designed capacity. In general, the sensing bulb should be placed on a horizontal section of the suction line exiting the evaporator.
