Solved Rear auxiliary heater. Floor=Heat, Vent=No Heat.

[Dora2007]

This is a “is it supposed to work this way” question. ’94 Aerostar with rear auxiliary heater.

In main control ‘floor’ position, both front and rear floor vents blow hot air. In main control ‘vent’ position, front vents blow hot air, but rear air gets directed to overhead vents and they blow cabin temp air, in other words not heated by rear heater core, but not cold either because AC if OFF. They just blow (useless) ‘plain air’ - no heat added.

So, does the rear system assume ‘vent’ means AC and does not draw air through heater core even when temp control is in the heat position? If I want hot air through front vent, I have to turn off rear heat because there is no added heat to the overhead vent.

If I want maximum heat, I have to choose ‘floor’, and then I get both systems blowing hot air to floor.

If this is normal operation, then what controls rear floor/overhead vent door position? I assume its vacuum same as front system. If no vacuum = floor, I need to identify vacuum hose going to rear control, cut and cap in winter and join normally in summer. If vacuum = floor, then I need to cut and route to extra full-vacuum in winter and join normally in summer.

That way rear goes to floor only (and adds heat) no matter what position front control is in - floor or vent.

Any insights? How does your van work?

 

[BrooklynBay]

Welcome to this forum! The front system uses a cable to switch between heat & A/C. Check the vacuum routing diagram under the hood to see how the rear controls work.

 

[Dora2007]

Welcome to this forum! The front system uses a cable to switch between heat & A/C. Check the vacuum routing diagram under the hood to see how the rear controls work.

Ok. Still begs the question: In the vent position, are the rear upper vents to draw air through the rear heater core, and therefore blow HEATED air? If in the vent position, the rear upper vents simply recalculate cabin air NOT through the heater core, then it is normal (and stupid) and there is nothing to fix.

 

[Josh P]

Ok. Still begs the question: In the vent position, are the rear upper vents to draw air through the rear heater core, and therefore blow HEATED air? If in the vent position, the rear upper vents simply recalculate cabin air NOT through the heater core, then it is normal (and stupid) and there is nothing to fix.

The front must be on heat or mix with the temp in the red to get heat in the rear only on the floor, at least on the 3 vans I have owned, I'd agree it is stupid and nothing to fix. The only reason it doesn't bother me is I might need the heater 1 week out of the year in phoenix.

 

[Dora2007]

The front must be on heat or mix with the temp in the red to get heat in the rear only on the floor, at least on the 3 vans I have owned, I'd agree it is stupid and nothing to fix. The only reason it doesn't bother me is I might need the heater 1 week out of the year in phoenix.

Ah, thanks. So now I will have to find the vacuum line that controls the floor/upper vent door and modify it to stay floor only, even if the front is in vent position, for winters only.

 

[Josh P]

Ah, thanks. So now I will have to find the vacuum line that controls the floor/upper vent door and modify it to stay floor only, even if the front is in vent position, for winters only.

Please update this thread when you make the modification.

 

[Dora2007]

Modification Success

Please pardon the detailed verbosity.

I obtained a vacuum and HVAC diagram. Indeed, the rear control door directs ‘Floor’ down thru the rear heater core, and directs ‘Vent’ up thru the A/C evaporator core. So, even in ‘Heat’ (no A/C), the ‘Vent’ position will draw cool floor air and blow it out the upper vent with no heating.

Looking at the vacuum control selector diagram, selecting ‘Vent’ instructs both front and rear vacuum doors to pull to the ‘Vent’ position. This is done thru a red vacuum hose that T’s to both door motors. Well, I want ‘Vent’ in front, but not in rear.

The good news is vacuum pulls the door to the ‘Vent’ position, so to block the vacuum will cause the door to stay in the default ‘Floor’ position.

Looking under the dash, I find a red vacuum hose running from the upper dash area along the left side kick panel, towards the doorsill cover. This is located 6” to the left of the brake lever, running along side a large wire bundle. It would make sense that this is the after-T line running to the rear only.

I cut the red vacuum line and cap the side that travels from the upper dash area, leaving the line traveling downward uncapped.

Success. Now when in the ‘Vent’ position, the front door moves to the ‘Vent’ position, and the rear door has no vacuum and stays in the ‘Floor’ position.

I have a small piece of rubber tubing on the lower red vacuum line. In the summer, when I want A/C ‘Vent’ both front and rear, I will re-join the line. In the winter, I will separate and cap the source feed.

All this is because in the ‘Floor’ position, the heat flow has never been that impressive, but in the ‘Vent’ position, there is much more heat directed at the driver and passenger. Leaving the auxiliary rear ‘Floor’ running adds heat to the big cold box that is the rear of the van.

Took me less time to do the mod than to write this.

 

[BrooklynBay]

I think that you should add a valve in the red vacuum line instead of capping it off, then reconnecting it every time you want the A/C to work. You could use a small valve with compression fittings or barbed fittings such as the type which is used with PEX tubing. You could put rubber hose over the barbed end of the valve, and connect it to the hard plastic red vacuum line.

 

[Josh P]

Thank you for following up with the details. Indiana gets pretty cold, the heater gets used for more months than the A/C. Valves would be nice but I'd cap it off too.

 

[BrooklynBay]

Could you take a picture of the area where the red vacuum line goes through under the dashboard? Please post a vacuum diagram too.

 

[Dora2007]

Could you take a picture of the area where the red vacuum line goes through under the dashboard? Please post a vacuum diagram too.

If only I knew how to post pictures. My description is pretty clear. This is a single red tube, 1/8" in diameter. All the wiring in that area is in wire bundles - this red tube is all alone. It comes from down from near the dash vacuum switch - floor-defrost-vent-A/C.

The 1/8” tube has about a 0.050” internal hole. Adaptation of that small hose to any ball valve would be quite a chore. Anyway, it’s separate & cap late fall and rejoin in late spring.

I found the diagram a bit down on a page:

http://www.justanswer.com/ford/26qp3-hello-i-m-trying-locate-main-vaccum-hose-plugs.html

It matches the diagram in my 1994 Aerostar Vacuum manual. Don’t know why I didn’t just look there first - I have the book.

I’d be happy to email pics if anyone can repost.

 

[BrooklynBay]

You could upload the photos to a hosting site such as WWW.PhotoBucket.Com, then embed them into a post.

 

[Dora2007]

Left side with kick panel, fuse box, and large wire bundle. Red plastic vacuum line runs along that wire bundle. NOTE: I have installed a remote starter - some extra wiring may be seen. There is a brown wire of my remote starter next to the red plastic vacuum line.

Closer view. Tie wraps hold vacuum line pieces. Upper one capped for winter. Lower one has joiner tube waiting for summer. In this photo angle, it may look like brown wire comes out of red vacuum line - look closer, it does not. Again, brown wire part of my remote starter install, won’t be there on yours.

Vacuum diagram. On the diagram, the little short piece from the T to the door motor is actually the piece that routes past the kick panel, under the doorsill, and to the rear heater assembly.

Actually, my original flow description is a bit faulty. In the vent (or A/C) position, air blows thru evaporator core to upper vents. In A/C, evaporator core is cold, so air is cooled. In Vent, evaporator core is ‘dead’, so air is not cooled, but it is not heated either.

In Heat, the air still passes thru the 'dead' evaporator core and is then directed down thru the heater core.

 

[BrooklynBay]

Thanks for taking the time to upload the photos, and a diagram. Your thread is now marked solved.