Carrier 28QX - Manual (Page 26)

• The collector circuit pump is operated thru a
relay (Rh) which is activated by the differential
controller. The differential controller monitors
the difference in thermistor temperatures (AT =
Tc — Ts). When this AT reaches 20 F, Rg is
energized, and the collector pump runs (also
the heat exchanger pump in the GL models). If
the pump is running and the AT drops to less
than 5 F, R6 is de-energized and the pump(s)
shut down.
MODE: HEATING
Controlling Mechanism:
• 2-stage room thermostat
Located in
90° Non-adjustable Aquastat storage tank.
Senses water
125 Adjustable Aquastat temperature to
Tri-X Coil.
• The 90° aquastat is factory set.
•
The 125° adjustable aquastat should be set
(between 95-125)* in the field as specified by
solar CLIC. (The set point is temperature at
which the QX coil water capacity can satisfy
the house heating design load.)
CAUTION; Do not set adjustable aquastat
above 125 F. Higher temperature can reduce
compressor life,
• The following chart defines the heating modes
as a function of water temperature (aquastats)
and room thermostat stages.
WATER TEMP
Above 125* F
(adjustable aqua­
stat set point)
Below 1255^F& ■
Above 90 F
(Non-adjustable
aquastat set
point)
Below 90 F
(Non-adjustable
aquastat set
point)
THERMOSTAT
1st Stage
I. Solar Only
- Tri-X Pump and
Indoor Fan On
li. Solar and Heat
Pump
— Tri-X Pump,
Compr., Outdoor
and Indoor Fan
On
III. Heat Pump Only
~ Compr., Indoor
and Outdoor Fan
On
2nd Stage
No Action
Strip Heat
Strip Heat
MODE; COOLING
The cooling modes are same as the 38HQ heat
pump system cooling operation with one excep­
tion. When the thermostat is in the cool position,
the differential controller is locked out; conse­
quently, the collector pump(s) will not run during
the cooling season. (When the domestic hot water
accessory is installed, this exception does not
apply.)
MODE: EREEZE PROTECTION OPERATION
The freeze protector is a thermostat placed on the
liquid line in the QX coil. It trips at 31 E and will
reset at 46 F. Consequently, the device can only
function in the following modes: defrost and
cooling. In each of these modes the freeze pro­
tector functions to prevent the coil from freezing,
but accomplishes this in different ways, as de­
scribed below:
Defrost cycle:
If the freeze protector trips, the Tri-X pump
will be turned on. The only way the defrost
cycle of the heat pump is affected is by
enhancing the defrost performance, by pro­
viding an additional source of heat besides the
indoor air.
Cooling cycle:
If the freeze protector trips, the compressor is
turned off and locked off until the thermostat is
reset. If the freeze protector does trip in
cooling, it is an indication of improper system
operation. This could be insufficient indoor air
or low refrigerant charge.
MAIIMTEiSIANCE AND SERVICE DATA
Pump Package
1. 34WA257/367 and 34GL257/367
a. Oil the Bell and Gossett collector (P2 —
Fig. 12 and 19)
• On start up and once a year
b. There is no maintenance required on the
Grundfos(Pi or?3 — Fig. 12 and 19) pumps.
2. 34GL167/257/367
a. Glycol level during operation
• On start-up charge the system with
enough glycol so that the level does not
drop below the sight glass during
collector pump operation.
• Check glycol level at least once a year
during collector pump operation.
b. Check inhibitor effectiveness in glycol once
a year.
Heat Pump, Indoor and Outdoor Fan and Coil,
Electric Heater and Storage Tank
1. Indoor components
a. Replace the filter once a year, sooner if it
becomes excessively dirty.
b. The 28QX036/042 should be checked and
bled of air as specified in the Start-Up
Instructions. This process should be per­
formed once a year.
c. When necessary to drain the water from
Tri-X coil, apply compressed air to the coil
water headers. Direct the air alternately thru
the entering water header and then the
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