Mounting The Thermostat; Heat Anticipator Setting; Temperature Setting; Subbase Setting - Honeywell T874R Installation Instructions Manual

T874R THERMOSTATS AND Q674L SUBBASES

Mounting the Thermostat

1 . Rem ove th e th erm o stat cover b y p u llin g th e b o tto m
edge o f th e cover aw ay fro m th e base u n til it snaps
free fro m th e cover clip .
N OTE: The cover is h in g ed at th e to p and can b e
rem o ved b y p u llin g o u t at th e b o tto m .
2. C arefully rem ove and discard p o lystyrene p ackin g
in sert th at p ro tects th e m ercury sw itches d u rin g
sh ip m en t.
3. Turn over th e th erm o stat base and n o te th e sp rin g
fing ers th at engage th e subbase contacts. M ake
sure th e sp rin g fing ers are notbent fla t, p reven tin g
p ro p er electrical co n tact w ith th e subbase.
4 . N o te th e tw o tabs o n th e to p in sid e edge o f th e
th erm o stat base. The tabs fit in to co rresp o nd ing
slots o n th e to p o f th e subbase. M o u n t th e th erm o ­
stat o n th e subbase.
5 . A lig n th e tw o cap tive m o u n tin g screw s in th e
th erm o stat base w ith th e p o sts o n th e subbase. See
Fig . 1 3 . T ig h ten b o th screw s.
o r dam age to subbase p osts can re su lt.
screw s
6 . H an g th e u p p er edg e o f th e th erm o stat cover o n to p
o f th e th erm o stat base and sw ing cover d o w n w ard
u n til it engages w ith th e cover clip .
Fig. 13. Mounting thermostat on subbase.
SETTINGS
A CAUTION
O n system s u sin g a gas valve, never ap ply a
jum p er across th e valve co il term in als, even
tem p o rarily. This can b u rn o u t th e th erm o stat h eat
an ticip ato r(s).

Heat Anticipator Setting

(2nd Stage Y594R1243)
Set th e h eat an ticip ato r scale to m atch th e p rim ary co n tro l
cu rren t d raw . W hen u sin g a T874 Therm ostat w ith tw o
stages o f h eatin g , set th e h eat an ticip ato r to m atch th e
respective p rim ary co n tro l cu rren t d raw . If th e p rim ary
co n tro l nam eplate has n o ra tin g o r if fu rth er ad justm ent is
necessary, use th e fo llo w in g p ro ced u re to d eterm in e th e
cu rren t d raw . M easure th e cu rren t d raw w ith th e th erm o ­
stat rem o ved and th e p o w er o n .
69-0392—9
D o not overtighten
1 . Connect an ac am m eter o f ap p ro p riate ran g e
betw een th e h eatin g term inals o f th e subbase:
Stage 2: b etw een W 2 and R .
2. M o ve th e system sw itch to H EA T.
3. A fter one m in u te, read th e am m eter and reco rd th e
read in g :
Stage 2:______________ am peres.
4. A fter m o u n tin g th e th erm o stat, set th e ad justab le
h eat an ticip ato r to m atch th e respective read in g
m easured in step 3 .
If eq u ip m en t cycles to o fast, set th e an ticip ato r to a h ig h er
cu rren t ra tin g , n o t m o re th an o n e-h alf d ivisio n at a tim e ,
and recheck cycle rate. M o st co nventio nal 2-stage h eatin g
eq uip m ent is designed to operate at 3 cycles p er h o u r p er
stage. See Fig . 1 4 .
M o st h eat p u m p system s should cycle 2 -1/2 to 3 tim es
per h o u r.
Fig. 14. Adjustable heat anticipator scale.

Temperature Setting

M o ve th e setp o in t lever to th e desired co m fo rt p o sitio n .
O ne lever co n tro ls b o th h eatin g and co o lin g .

Subbase Setting

System sw itch in g p o sitio n s co n tro l th erm o stat o p eratio n as
fo llo w s:
OFF: H eatin g and co o lin g system s are o ff. If th e fa n
sw itch is at th e AUTO p o sitio n , th e co o lin g fan is
also o ff.
H EA T: H eatin g system is co n tro lled b y th e th erm o stat.
C o o ling system is o ff.
COOL: C o o lin g system is co n tro lled b y th e th erm o stat.
H eatin g system is o ff.
EM .H T.: Em ergency h eat relay is energized o n call fo r
h eat. C o o ling system is o ff. Com pressor is de­
energized.
Fan sw itch in g p o sitio n s co n tro l fan o p eratio n as fo llo w s:
O N : Fan operates co n tin u o u sly.
AU TO : Fan operates as co n tro lled b y th e th erm o stat.
To sw itch p o sitio n s, use th u m b and ind ex fin g er to slid e
lever to d esired p o sitio n . Sto p sw itch lever in d eten t
d irectly o ver th e desired fu n ctio n in d icato r m ark fo r p ro p er
circu it o p eratio n .
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