Max A/C = closed heater core valve

[brages]

An interesting feature on my 1997 Ranger: when you turn the A/C all the way to the "max" setting, the valve for the heater core closes. So you cannot adjust the temperature of the air coming out the vents if it's on "max".

A plus of this system is if your blend door gets messed up, your A/C should still blow cold on "max". I don't think this design plays well with automatic climate controls though. Another plus is you don't have a hot heater core in the middle of your dash barely separated from the air flow.

Do you have a car that does this? I know the old Chevrolets had a "max" setting on the A/C, and I know they had a heater valve, but I don't know if they used this logic.

 

[SHOZ]

I bought one of these valves to use as an experiment but put it aside many years ago. Most vehicles don't have this as they want constant flow through the heater core so it doesn't plug up AKA Ford 3.0L Vulcan in the late 90s.

 

[Braapdaddy]

I converted one of my powestrokes to a closed heater core for the summer .......makes a huge difference on the cold output on the air

 

[CorvairGeek]

Full size GM 'B-Bodies' did that from at least '77-90.

 

[Kira]

Thoughts:
1) I think the heater core on newer vehicles is part of the old "bypass" system. Coolant circulates in a cold engine through this system to heat it up evenly......even with the thermostat closed.

2) My 2005 Ranger (4.0l SOHC) has the same thing. Which engine do you have?
There's a 7" metal globe vacuum reservoir which pulls the coolant valve closed when you go to MAX.
It strikes me as a lot of hardware a simple cable controlled valve could've replaced.

 

[BMWTurboDzl]

My BMW has a HCV and the "Max" button overrides the "Auto" temp feature. Makes sense IMO.

 

[brages]

I bought one of these valves to use as an experiment but put it aside many years ago. Most vehicles don't have this as they want constant flow through the heater core so it doesn't plug up AKA Ford 3.0L Vulcan in the late 90s.

That's funny, I had a '98 Ranger 3.0 that had a plugged heater core. Coolant was all rusty, too.

 

[brages]

I guess this doesn't belong in Mech/Maintenance... I wasn't thinking when I posted it.

 

[dumkid]

My dad keeps putting ball valves on his coolant hoses to make his a/c colder. I'll probably do it to my car eventually

 

[Dave9]

So you cannot adjust the temperature of the air coming out the vents if it's on "max".

Sure, max means max, as cold as it can get, but you can still adjust how cold the cabin gets to "some" extent, by how high the blower is set.

 

[SHOZ]

Max just means recirculate and highest fan speed, on the cars I've had.

 

[cb_13]

Even my 78 f250 has the vacuum actuated water valve that shuts off flow to the heater core with the ac turned on.

 

[brages]

Here is something fun... My blend door on my Ranger HAS just failed. Since it cuts off flow to the heater core, max ac is still good and cold, but every other ac setting gets warmish air.

 

[Braapdaddy]

Here is something fun... My blend door on my Ranger HAS just failed. Since it cuts off flow to the heater core, max ac is still good and cold, but every other ac setting gets warmish air.

There is a new blend door from Dorman that has a metal square instead of plastic I have done a few

 

[meep]

My 2006 tundra had a valve to quench the heater line. I don’t know the conditions under which it would close. Air was ice cold in that thing.