What is the piece that the hoses are connecting to in the picture. It is the source of my mysterious coolant leak and dont want to be taken for a ride at the shop.

It is under the air filter on the passenger side

 

From the picture it looks to me like a coolant flow control valve,when you have the max A/C selected it closes by vacuum to stop coolant flow through the heater core.

CC

 

I agree. But I think it shuts off anytime A/C is selected to keep the heater core cool.

 

Negative.

The heater core has nothing to do w/the A/C. (only heating)

The heater system has a valve that allows hot engine coolant through the heater core at a rate from 100% to 0%



This is how you can run your A/C and still have heat blasting from the vents... or how the the tahoe runs the a/c when it's 60 out, and your car is set to 74... by passing the air through the evaporator, then the heater core, it dries it out, makes it nicer.


http://www.certifiedmastertech.com/w...am-233x300.jpg

Air conditioning - Wikipedia, the free encyclopedia

Love to Learn!

 

That may be what they do now w/ the auto temp control but they used to use a vacuum signal to either open or close the water valve to the heater core depending on what mode you had selected.

The valve pictured appears to be vacuum controlled and not sure how you'd modulate the water flow from 0% to 100%.

 

You have the function right, but your missing the part where the system has the ability to partially open / close the valve. it's not a all or nothing. if it was, you'd either have full heat or none.

On my '95 it was, like you said run by a vaccum, because that makes it easier to turn the ***** on the dash, on lower end cars the valve can be actuated by a 'direct' link, which gives you hard to turn / move dash *****. (ford escape, jeep wrangler, etc) either for cost or durability

the vaccum applied to the valve is directly proportional to the **** on the dash.

if the coldest setting on the **** is selected, the vaccum goes full suck (or release, i'm not sure) closing the valve and if the hottest setting is selected it goes full opposite. (full open)


and anywhere in between... if you put it on the center, it sets the valve to 50% so some heat goes through the heater core...


or say you have it on 25% heat on the ****, the valve opens 25%

this allows the heater core to change temperatures, even though the engine is always 210 (or about)

I should have just googled it:

http://en.wikipedia.org/wiki/Heater_core#Control

 

yes, that is a coolant valve and it is available at an autoparts store for cheap. I recently replaced mine without too much trouble.

 

So they are modulating the amount of vacuum going to the valve? Interesting.

I think it would be a lot easier to control the temp w/ a blend door and just run the heater core full on. Will have to look at mine to see where this valve is.

 

some cars do, do it, that way. usually cheaper ones...

Mercedes feels you shouldn't have to wait to get heat from your $80,000 car... so they put electric heating elements in the path of the HVAC... so u get heat from the second you turn the key...