Hello Hemanth,

Below a PID control algorithm non very scientific but functional.
Convert to your prog. language and try it.

; LFFMPID
; PID routines for refr/heat
; By Luiz Fernando Mosca
; Ibracon - Brazil

; Inputs:
;
; _VAR= Input Var(Sensor)
; _SPT= Setpoint Adj(Parm)
; _INT= Integer Var(Parm) in RPM repeat per minute time loop depend
; _DIF= Differential Var(Parm)
; _ZMT= Dead Zone (see diag.)
; _BTA= Proportional Heating Band
; _BTR= Proportional Refrigeration Band


; RREF for refrigeration out

IF _AQU_OLD = 0 THEN

_ISUM=_ISUMR
_OLDVAR=_OLDTEMP

_PERROR=(_SPT + _ZMT/2) - _VAR
IF _BTR<=0 THEN _ERRO=0 ELSE _ERRO=(_PERROR / _BTR) * 100
_INTG=.01 * _ERRO
_ISUM=-1 * (_INT / 100) * _INTG + _ISUM
IF _ERRO >= 0 THEN _ISUM=0
IF _ISUM < 0 THEN _ISUM=0 ; Anti reset windup function (optional)
IF _ISUM > 100 THEN _ISUM=100
_DERIV=_VAR - _OLDVAR :_OLDVAR=_VAR
_OUT= -1 * _ERRO + (_DERIV * _DIF) + _ISUM
IF _OUT<0 THEN _OUT=0
IF _OUT>100 THEN _OUT=100
_ISUMR=_ISUM
_OLDTEMP=_OLDVAR
_OUTREF=_OUT

ELSE

_REF_OLD = 0
_OUTREF = 0

ENDIF



; RCAL for heating out

IF _REF_OLD = 0 THEN

_ISUM=_ISUMA
_OLDVAR=_OLDTEMP
_PERROR=_VAR - (_SPT - _ZMT/2)
IF _BTA<=0 THEN _ERRO=0 ELSE _ERRO=(_PERROR / _BTA) * 100
_INTG=.01 * _ERRO
_ISUM=-1 * (_INT / 100) * _INTG + _ISUM
IF _ERRO >= 0 THEN _ISUM=0
IF _ISUM < 0 THEN _ISUM=0 ; Anti reset windup function (optional)
IF _ISUM > 100 THEN _ISUM=100
_DERIV=_OLDVAR - _VAR :_OLDVAR=_VAR
_OUT= -1 * _ERRO + (_DERIV * _DIF) + _ISUM
IF _OUT<0 THEN _OUT=0
IF _OUT>100 THEN _OUT=100
_ISUMA=_ISUM
_OLDTEMP=_OLDVAR
_OUTAQU=_OUT

ELSE

_AQU_OLD = 0
_OUTAQU = 0

ENDIF


; Outputs:
;
; _OUTREF= Output to Refrigeration Actuator
; _OUTAQU= Output to Heating Actuator



; Output Diagram:
;
; _SPT
; _OUTAQU | _OUTREF
; ------- | ---------
; | /
; | /
; | /
; | /
; | /
; | /
; | /
; ---------------------------|-----/------------------------->_VAR
; -------|--------------|-----------|---------------|----------
; _BTA _ZMT _BTR



; USING AND DISTRIBUTING THE LFFMPID PID ROUTINES
; ===================================================
;
;LFFMPID may be used in any way, for any purpose, at no cost. It may be
;distributed by any means, provided that author mention or the original
;files as supplied by the author remain intact and no charge is made other
;than for reasonable distribution costs.
;
;You do not need to register to use LFFMPID, or buy a licence to use it,
;but we would appreciate your feedback.
;
;LFFMPID may not be distributed with any commercial product without a prior
;license agreement with Ibracon Controles Eletronicos Ltda.
;email: ibracon@inf.ufrgs.br
;
; THE INFORMATION AND CODE PROVIDED IS PROVIDED AS IS WITHOUT WARRANTY
; OF ANY KIND, EITHER EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO
; THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
; PURPOSE. IN NO EVENT SHALL IBRACON C.E.LTDA. BE LIABLE FOR ANY DAMAGES
; WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL, CONSEQUENTIAL, LOSS
; OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF IBRACON C.E.LTDA. HAS
; BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGES.
;
;Author: Luiz Fernando Mosca
; lfmosca@portoweb.com.br
;
;----------------------------------------------------------------------------


Best regards.

Luiz Fernando Mosca
lfmosca@portoweb.com.br