Gentlemen,
I need your help again. I am installing an under-dash AC/Heating unit and need to tap into my heater hose. I am thinking that the flow in the picture is from the back to the front? Is that correct?
Thank you,
Charlie D.

 

See Joe's diagram in second post...
https://classicoldsmobile.com/forums...5-no-c-179150/

 

Thank you!!

 

The port at the rear of the intake goes to the inlet of the heater core. It is 5/8" hose. The port at the water pump is the outlet from the heater core. It is 3/4" hose. The larger hose is always the return line because the pressure is lower after passing through the core.

 

Charlie , In your picture you have the 2 coolant lines connected , that means you needed a 5/8 to 3/4 inch adaptor or maybe the 3/4 hose is too big for the 5/8 fitting on the intake manifold . i have a few older cars , i always have a 5/8 to 3/4 coolant hose adaptor with me if i go out of town in case a heater core lets go .

Another way to word this is , The smaller 5/8 hose coming from the back of the engine is the pressure side of the flow . The larger 3/4 hose at the water pump is the vacuum side of the coolant flow / vacuum side of the pump . As any pump has a vacuum side and a pressure side.

With cars that have AC there is a coolant flow shut off valve mounted to the intake manifold at the back , or just off the back of the engine . The coolant shut off valve is vacuum controlled . So when the AC control on the dash is in the AC MAX position , the valve closes . Stopping hot coolant from going to the heater core . So what i am getting at is seeing that AC cars came from the factory with a coolant shut off valve in the 5/8 pressure side , cars with no AC could install a shut off valve in the 5/8 pressure side, to stop coolant flow to the heater core in very hot weather . I have AC in my car but still installed an extra inline shut off valve , i close it off in hot weather / helps keep the cabin cooler, most days do not even need the AC on !
I would also think this extra coolant shut off valve would be a good idea for race cars that have a heater core or drivers that have a heavy foot , protects the heater core when engine is at red line .

Charlie another thing to keep in mind if you replace the 5/8 coolant hose fitting on the intake manifold .The fitting has a restriction , or it will be too much flow / pressure going to the heater core . ThIs nipple with restrictor was mentioned by Joe in his May 4 / 2024 above link / post.
Charlie would you like pictures of inline shut off valves and fittings i used . or maybe thats a new topic / thread ! or email me , you have my email.

 

Don't over-think this. I've used a 5/8" connector and just clamped down harder on the hose clamp.