Does anyone know why there are 3 #21 shut off valves

Does anyone know why there are 3 #21 shut off valves

Postby Rinny [OP] » February 25th 2017, 1:45pm

Does anyone know why there are 3 #21 shut off valves listed for the rear heat?
http://www.wholesalegmpartsonline.com/p ... 70012.html
click the second diagram down.
03Astro AWD/4WD
5.7L+30,SS dual exhst,mild cam,Efan,CAintake
2100lb Springs,Jour Hangers/Shackles,3" Alum Blocks
TorsenDiffs,3:73'S,VettServo
NP236TC
Dual Piston Rear Calipers
GY DTrac 235/85/R16
ARB &/Custom bumpers
2x6x1/4 Rockrails
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Re: Does anyone know why there are 3 #21 shut off valves

Postby MI_Ghost » February 25th 2017, 2:42pm

Easy enough.
1. 4 port valve for standard front heater. No rear heat. Delco 15-5557 (Should be #20)
2. 2 port valve for rear heat only. Delco 15-5586 (Vacuum operated)
3. 2 port valve for rear heat w/ AC shut off. Delco 15-5877 (Shuts off AC when rear heat is used)(Vacuum/Electric)
4. 6 port valve for front and rear heat. Delco 15-5551 (#20)

Numbers 2&4 or 3&4 are used together with supply going from engine to 6 port valve to 2 port valve the to rear heater core. Return is routed directly back to 6 port valve. This allows the rear heat to be shut off when not needed.

All 4 valves are still readily available. Shop around for the best price.

And for reference.
#12 Delco #15-30578 is the vacuum hose that controls the vent location selection (No Dash vents issue)
~Ghost
Ast' Cargo: 2001 Astro Cargo
Beauty: 2009 Impala LT
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Re: Does anyone know why there are 3 #21 shut off valves

Postby Rinny [OP] » February 26th 2017, 8:27pm

Thank you. Very helpful post!!
03Astro AWD/4WD
5.7L+30,SS dual exhst,mild cam,Efan,CAintake
2100lb Springs,Jour Hangers/Shackles,3" Alum Blocks
TorsenDiffs,3:73'S,VettServo
NP236TC
Dual Piston Rear Calipers
GY DTrac 235/85/R16
ARB &/Custom bumpers
2x6x1/4 Rockrails
Original Poster [OP]
User avatar
Rinny
V8 Swap Achievement
V8 Swap Achievement
Firing on 3 Cylinders (L2)
Firing on 3 Cylinders (L2)
Years of Membership: Rinny has been a member for 4 full yearsRinny has been a member for 4 full yearsRinny has been a member for 4 full yearsRinny has been a member for 4 full years
Posts: 1339
Topics: 56
Images: 6
Joined: December 2015
Alias (AKA): 5.7L, NP236, 3"Lift
Van Model Year: 2003
Van Make/Model: Chevrolet Astro
Extra Info: 5.7L NP236


 
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