Gaymar MEDI-THERM II MTA5900 Series, Руководство по обслуживанию

Страница: 14 / 83

SERVICE MANUAL
Medi-Therm II
THEORY OF OPERATION
w
w
w
.g
aymar
.com P/N 10187-000 7/98
WATER TEMPERATURE CONTROL
Hot and cold solenoid valves regulate the flow path by directing water
returning from the blanket to either the hot or cold water reservoir.
Regulating the flow path controls the temperature of water pumped to the
blanket. The microprocessor controls solenoid valve operation. Only one valve
may open at a time:
When the HEAT status light is lit, the hot solenoid valve is open.
Water returning from the blanket circulates through the hot water
reservoir and is heated before being pumped back to the blanket. The
heater, pump, and hot solenoid valve are energized. (See figure 10, p.
70.)
When the COOL status light is lit, the cold solenoid valve is open.
Water returns from the blanket to the cold water reservoir and is
replenished by chilled water from the cold water reservoir before
being pumped back to the blanket. The pump and cold solenoid valve
are energized. (See figure 11, p. 70.) The refrigeration compressor
maintains the
cold water reservoir temperature and operates independently of the
solenoid status.
When the IN-TEMP status light is lit, either the blanket water temperature is
within 1.8°F (1°C) of the setpoint (in MANUAL mode) or the patient
temperature is within 1.8°F (1°C) of the setpoint (in AUTO mode). Water
temperature is controlled by alternating between heating and cooling (See
figures 10 and 11).
REFRIGERATION UNIT
The refrigeration circuit (see figure 12, p. 71) consists of two heat exchangers
operating at two pressures and two devices used to change these pressures. The
first of these devices is the compressor which changes the gas pressure from low
to high. The other device is the capillary tube which reduces the refrigerant
pressure from high to low.
Beginning the cycle at the capillary tube, high pressure liquid refrigerant flows in
the capillary tube and is discharged into the evaporator coil. The evaporator coil,
which is a heat exchanger, receives the refrigerant as a mixture of liquid and
vapor at a pressure low enough so that it boils and absorbs heat from the water
surrounding it.
The heated refrigerant vapor then leaves the evaporator coils, enters the suction
side of the compressor and is compressed, causing its pressure and temperature
to increase. The vapor, much warmer than the ambient air, travels to the
condenser.
The condenser is the other heat exchanger. The condenser fan draws the colder
ambient air over the condenser coils and removes the heat being carried by the
refrigerant and causes it to condense back into liquid refrigerant. This completes
the cycle and the high pressure liquid refrigerant is returned to the capillary tube
to be used over again. The temperature of the water surrounding the evaporator
coil (in the cold water reservoir) is controlled by the microprocessor. The
microprocessor senses the temperature with a cold water reservoir probe and
cycles the compressor relay on and off.
6.1 THEORY OF
OPERATION,
MEDI-THERM II
MACHINE (continued)
10