MasterCool 99903 Gebrauchsanweisung Seite 5

NOTE: The unit will shut down after 15 minutes automatically. Press the POWER button again.
Allow 30-45 seconds for initializing and the correct vacuum reading to appear. Once the target
vacuum is reached, close the vacuum valve and disconnect the vacuum gauge port from the
system. Press the POWER button to turn the unit off. (If pressure, temperature or deep vacuum
is being used for an extended period of time turn the unit off and turn back on again when
reading is required.)
WARNING!! Never stop the vacuum pump unless the vacuum gauge is discon-
nected. Failure to do so may cause oil to enter the sensor chamber.
IMPORTANT: When checking a system for leaks under high vacuum (less than 1000
microns), connect the vacuum gauge directly to the system. If additional connections are
required use copper tubing (do not use rubber hoses) and high vacuum shut-off valves.
Standard hoses and manifold gauge set shut-off valves may have a small amount of leak-
age under high vacuum. When initiating a high vacuum test, the vacuum gauge reading
may "drift" higher until the system has equalized. After this short stabilization period (5
minutes) the vacuum reading should hold steady. An upward "drift" of the vacuum gauge
reading may indicate a leaking system.
MEASURING ACTUAL SUPERHEAT AND SUBCOOLING
Superheat is the difference between the actual temperature (sensor temperature) of the
refrigerant (gas) as it leaves the evaporator and the boiling point temperature of the refrigerant
in the evaporator coil (saturated temperature). After boiling, the refrigerant continues to warm
up. The number of degrees it "warmed up" after boiling is called the superheat. Under worst-
case conditions (low load for fixed orifice systems), the refrigerant in the evaporator boils off near
the end of the evaporator coil. To make sure liquid doesn't enter the compressor under the worst
case condition, the AC manufacturers publish charts. The charts indicate what the superheat
should be at a given indoor wet bulb measurement and outdoor air temperature. Measuring
superheat is your best indication on a fixed orifice system of the proper refrigerant charge and
operating conditions. If everything else is working properly and the actual superheat is too high,
add refrigerant. If it's too low, remove refrigerant.
Subcooling is the difference between the boiling point of the refrigerant in the condenser
(saturated temperature) and the actual temperature (sensor temperature) of the refrigerant
as it leaves the condenser. The degrees that the refrigerant "cools down" below the boiling point
is the sub-cooling. Under worst case scenario low load for thermostatic expansion valve systems
(TXV) the subcooling will continue to rise. If the subcooling rises too high, liquid may be backed
into the compressor causing damage and failure.
FIG. C
LOW HIGH
REF
VAC
Liquid
Vapor and Liquid
Vapor
On TXV systems, the subcooling is the best indication of the state of the charge in the refrigerant
system since these systems are designed to maintain constant superheat. Properly charging a
system ensures maximum efficiency and longer equipment life.
Use caution whenever working with electricity and high-pressure liquid or gas.
Always wear safety glasses.
Follow all instructions provided with equipment being serviced or installed.
TARGET SUPERHEAT AND SUBCOOLING
Follow all equipment manufacturer's specifications, warnings and suggestions. To determine the
target superheat (fixed orifice system) or subcooling (charts vary dramatically from one system to
another), you will typically need three things. Outdoor dry bulb (outdoor air temperature), indoor
Throttle Valve (TXV, Cap Tube, Fixed Orifice)
Condenser
www.mastercool.com
(SEE FIG. C)
Compressor
Liquid
Evaporator
Vapor and Liquid
Vapor
LOW HIGH
REF
VAC
5