Carrier 50RTG - Manual (Page 17)

17
NOTE: Three factors determine the operating limits of a unit:
(1) entering air temperature, (2) water temperature and (3)
ambient temperature. Whenever any of these factors are at a
minimum or maximum level, the other two factors must be at a
normal level to ensure proper unit operation. See Table 15.
Table 15 — Operating Limits — 50RTG Units
LEGEND
NOTE: Value in heating column is dry bulb only. Any wet bulb read-
ing is acceptable.
Scroll Compressor Rotation — It is important to be
certain compressor is rotating in the proper direction. To
determine whether or not compressor is rotating in the proper
direction:
1. Connect service gages to suction and discharge pressure
fittings.
2. Energize the compressor.
3. The suction pressure should drop and the discharge
pressure should rise, as is normal on any start-up.
If the suction pressure does not drop and the discharge
pressure does not rise to normal levels:
1. Turn off power to the unit. Install disconnect tag.
2. Reverse any two of the unit power leads.
3. Reapply power to the unit and verify pressures are correct.
The suction and discharge pressure levels should now move
to their normal start-up levels.
When the compressor is rotating in the wrong direction, the
unit makes an elevated level of noise and does not provide
cooling.
After a few minutes of reverse operation, the scroll com-
pressor internal overload protection will open, thus activating
the unit lockout. This requires a manual reset. To reset, turn the
thermostat on and then off.
NOTE: There is a 5-minute time delay before the compressor
will start.
Unit Start-Up Cooling Mode
1. Adjust the unit thermostat to the warmest position.
Slowly reduce the thermostat position until the compres-
sor activates.
2. Check for cool air delivery at unit grille a few minutes
after the unit has begun to operate.
3. Verify that the compressor is on and that the water flow
rate is correct by measuring pressure drop through the
heat exchanger using P/T plugs. Check the elevation and
cleanliness of the condensate lines; any dripping could be
a sign of a blocked line. Be sure the condensate trap in-
cludes a water seal.
4. Check the temperature of both supply and discharge
water. If temperature is within range, proceed. If tempera-
ture is outside the range, check the cooling refrigerant
pressures.
5. Air temperature drop across the coil should be checked
when compressor is operating. Air temperature drop
should be between 15 and 25 F.
Unit Start-Up Heating Mode
NOTE: Operate the unit in heating cycle after checking the
cooling cycle. Allow five minutes between tests for the pres-
sure or reversing valve to equalize.
1. Turn thermostat to lowest setting and set thermostat
switch to HEAT position.
2. Slowly turn the thermostat to a higher temperature until
the compressor activates.
3. Check for warm air delivery at the unit grille within a few
minutes after the unit has begun to operate.
4. Check the temperature of both supply and discharge
water. If temperature is within range, proceed. If tempera-
ture is outside the range, check the heating refrigerant
pressures.
5. Once the unit has begun to run, check for warm air deliv-
ery at the unit grille.
6. Air temperature rise across the coil should be checked
when compressor is operating. Air temperature rise
should be between 20 and 30 F after 15 minutes at load.
7. Check for vibration, noise and water leaks.
Flow Regulation — Flow regulation can be accom-
plished by two methods. Most water control valves have a flow
adjustment built into the valve. By measuring the pressure drop
through the unit heat exchanger, the flow rate can be deter-
mined. See Table 16. Adjust the water control valve until
the flow of 1.5 to 2 gpm is achieved. Since the pressure con-
stantly varies, two pressure gages may be needed in some
applications.
An alternative method is to install a flow control device.
These devices are typically an orifice of plastic material de-
signed to allow a specified flow rate that are mounted on the
outlet of the water control valve. Occasionally these valves
produce a velocity noise that can be reduced by applying some
back pressure. To accomplish this, slightly close the leaving
isolation valve of the well water setup.
Flushing — Once the piping is complete, final purging and
loop charging is needed. A flush cart pump of at least 1.5 hp is
needed to achieve adequate flow velocity in the loop to purge
air and dirt particles from the loop. Flush the loop in both direc-
tions with a high volume of water at a high velocity. Follow the
steps below to properly flush the loop:
1. Verify power is off.
2. Fill loop with water from hose through flush cart before
using flush cart pump to ensure an even fill. Do not allow
the water level in the flush cart tank to drop below the
pump inlet line to prevent air from filling the line.
3. Maintain a fluid level in the tank above the return tee to
avoid air entering back into the fluid.
4. Shutting off the return valve that connects into the flush
cart reservoir will allow 50 psi surges to help purge air
pockets. This maintains the pump at 50 psi.
5. To purge, keep the pump at 50 psi until maximum pump-
ing pressure is reached.
AIR LIMITS COOLING HEATING
Rated Ambient Air 80° F 70° F
Min. Entering Air 50° F 40° F
Rated Entering Air db/wb 80/67° F 70° F
Max. Entering Air db/wb 110/83° F 80° F
WATER LIMITS
Min. Entering Water 25° F 25° F
Normal Entering Water 85° F 70° F
Max. Entering Water 115° F 115° F
db — Dry Bulb
wb — Wet Bulb
To avoid possible injury or death due to electrical shock,
open the power supply disconnect switch and secure it in
an open position before flushing system.