Rear heater core hoses HOT with AC on? Need diagram maybe?

[Pinky 1352]

2003 Expedition XLT 4.6L 2WD w/ manual rear AC

Trying again this year to get the AC system working correctly, and I *think* all system leaks may finally be addressed.

I was doing my own check for leaks after the mechanic redid some seals for me and I noticed that the hoses going to and from the rear heater core are super hot.

The vacuum controlled heater control valve in the engine compartment appears to be functioning as intended for this year (only in the closed position on Max AC), and the *front* heater core hoses are cool(ish) so why would I still be getting hot coolant to the rear core?

It kind of negates having rear AC at all if the blower behind the AC core back there also has to blow past a hot heater core?!


I haven't been able to find a comprehensive diagram for the heater hose routing so if anyone has that instead of an answer I can maybe figure this out?


Thanks in advance all!

 

[Hamfisted]

Yes, the rear heater hoses are free flowing hot water. Temperature is just regulated with a blend door back there. It's just the way they engineered it. When you have it in the cold air position it's just recirculating cabin air, not outside air. When you ask for warmer air it starts to open the blend door, that pulls through the heater core. Actually I just ran it full cold and unplugged the temp actuator back there. It breaks so often I got tired of replacing it anyway. I'm in south Florida and rarely ( i.e. never....) need hot air from the back. So I can just moderate cabin temperature from the front pretty easy.







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[Pinky 1352]

It still seems to negate some of the possible potential cooling if the rear heater core is *always* hot back there. There's not much insulation between the rear cores with that flimsy blend door

I've decided to mod this puppy by putting in a second heater control valve in the engine compartment so that the rear heater core will also be controlled by vacuum when I'm on Max AC.

I live in Las Vegas and *ANY* less heat in this car somewhere can only help!

I can't really install it on the line to control both of lines at once because of the way the hose bends (red arrow) so I'm having to opt adding a second one in at where the blue arrow points (that hose goes to the rear heater core input. The hose under that one is the return).
I'll simply also add in a vacuum line tee and splice to that to control the new valve.

Even if I shave off a few degrees in the cabin the quick under $25 job for the part will be worth it!


Unless someone here can tell me why this might not be a good idea?

 

[Hamfisted]

How 'bout just putting a stainless ball valve there in that line where your blue arrow is ? You'll probably never open it, but if you need to you can.
That way no extra vacuum plumbing is needed and it looks clean. Maybe you're on to something? Let us know how it works out.


5/8" Stainless Ball Valve on Amazon







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[Pinky 1352]

The simple ball valve might've been an option but I had already ordered another heater valve (Motorcraft YG368 Heater Valve) for slightly under $21 from Amazon.
I already had hose clamps and vacuum line tees handy.

The whole job took under 10 minutes to do and I didn't even spill a drop of coolant because I placed a small Tupperware bowl under the hose before I cut it.

I *was* worried that maybe the available vacuum wouldn't be enough to close both valves, but they work perfectly.

First photo is car off with no vacuum applied, and second is car running with Max AC on, and you have to zoom in but you can definitely see the the arm that controls the inner valve has moved.


I guess I won't know how much of a internal cabin temperature difference this really makes until June or July, but my intuition is telling me it sure can't hurt!

 

[whtbronco]

Nice. How could that not help! Stop the flow of coolant and the heater core will be cooler.

 

[Pinky 1352]

For all following this...


I found the reason NOT to do that heater valve in that line, at least not the way I did it!

I should have taken a piece out of the original hose roughly the size of the heater valve.

Apparently even though the hose moved easily to get that extra heater valve in, the plastic in the original quick connect hose connector going to the rear heater core was fragile after 25+ years and must've cracked and is now leaking.
I'm assuming from the slight extra pressure on it, and because that heater valve is in an always open position until vacuum is applied.


And I guess since it was actually warmer today made the coolant expand just enough to start a gravity fed leak?

My coolant reservoir is really low now.

I'm having to order an overnight replacement part from Amazon and I can change THAT out tomorrow.
I ordered a set of TWO new connectors and will swap out both send and return line connectors because if ONE was that fragile the other will be also.
May as well head off some future disaster!

In the meantime I've Velcro-ed the heater hose valve arm in the closed position to stop the rest of reservoir from draining.

Good thing I had to go out to that side of the house to move my trash bins for tomorrow pickup and saw the puddle




Photo shows those line connectors. Hard to get a phone camera in there but if you look close you can see that the rear connection is wet (that's the "send" line , the front is the return)
I'm assuming the white plastic piece in the connector broke?

 

[whtbronco]

Well that sucks, though thankfully it shouldn't be too costly or difficult to resolve. The white part is just a connector/lock. Just beyond that there are 2 o-rings in the black plastic tube and they have likely hardened over the years. As you noted moving it around while installing the heater valve jostled it just enough to cause a leak probably with the hardened o-rings.

I have all new coolant hoses with connectors to install on mine next month when I do the timing set. Figured since one of the heater hoses is beginning to soften it's time and I am concerned the o-rings will give out before long. All of mine are original which is quite frankly amazing to me, I can't believe the factory hoses lasted 21yrs.