Service Function - Carrier 040-420 Installation And Service Manual

0" to 20" F (0" to 11" C). This is maximum amount leav-
ing chilled water point is to be increased.
set
2. Maximum Reset Reference (CREF2) - allowable range
0" to 20" F (0" to 11" C). This is the cooler temperature
drop at which reset reaches its maximum value.
3. Minimum Reset Amount (CRSTl) - allowable range
ing chilled water set point is to be increased when reset
is initiated.
4. Minimum Reset Reference (CREFl) - allowable range
0" to 20" F (0" to 11" C). This is the cooler temperature
drop at which reset is at its minimum value. (Reset be-
gins here .)
NOTE: Reset set points are not accessible unless the reset
function is enabled first. This is done as a field configura-
tion. Select one of the 3 choices for type of reset: Return
Fluid Reset, External Temperature Reset, or 4-20 mA Ex-
ternal Signal (with a loop isolator) Reset.
If dual set point control is enabled (see Field Wiring sec-
tion on page 7 1), the amount of reset is applied to which-
ever set point is in effect at the time.
Example 5 demonstrates how to activate reset. Example
6 demonstrates how to change the type of reset. Assume
that reset is to be based on return water temperature, the
desired reset range is to be 2" to 10" F (1" to 5.5" C) and
full load is a 10" F (5.5" C) drop across the cooler. See
Fig. 4.
Activating reset based on external temperature or
4-20 mA signal is done the same way, except the reference
set point range is 20" to 125" F (-6.6" to 5 1.6" C), or 4 to
20 mA depending on which method was selected at the field
configuration step.
9
8
7
2 3 4
RESET REFERENCE TEMPERATURE (COOLER EWT-LWT)
Fig. 4 - Cooling Return W a t e r Reset
40
Example 5 - Using Return Water
Temperature Reset
KEYPAD DISPLAY
ENTRY
RESPONSE
FLD CFG
C S P T Y P X
CRTYP 0
C R T Y P
S E T P O I N T
R E S E T
C R S T 2 0 0
C R S T 2 1 0 0
CREF2 0.0
CREF2 1.0
CREFl 0.0
5 6 7
COMMENTS
Field configuration
subfunction of

service function

Scroll past single/dual
Display shows no reset
type has been selected
Return water temperature
1
is selected and activated
System set points
Present occupied chilled
water set point
Enter new chilled water
set point
Reset set points
maximum reset
Cooling maximum reset
is 10 F
Cooling maximum reset
reference is 0" F
Cooling maximum reset
reference is 1 F
Cooling minimum reset
0 0
is 0" F
Cooling minimum reset
is 2 F
Cooling minimum reset
reference is 0" F
Cooling minimum reset
reference is 8 F
I
8 0
6 0
0
8 9