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Topics regarding the climate control in the cabin of the van. Discuss things like air conditioning, refrigerant recharging, and dual climate controls, a/c vents, accumulator or defrosters, heater core, or fan inside the van.
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Does anyone know why there are 3 #21 shut off valves

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.

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

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)

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

February 26th 2017, 8:27pm

Thank you. Very helpful post!!
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