Hey all, I am doing the heater core a/c mod, and picked up a motorcraft vacuum bypass valve, and now am having a problem finding the correct vacuum line to tie in to. There are a few right by where the valve is, two red and one black, but I don't want to chop any until I know which one is correct.

My van is a '93 E150 with the 4.9L engine. No aux heat or air if that matters. Anyone know off hand which one I should T in to? Thanks

Brew

 

Hey Brew---I did a write up on this mod a while back can re-post it here again with photos but it might be more than you're looking for, its fairly detailed about doing the mod from the start.

Let me know------its ready to go if interested.

 

I would love it if you could repost it. I did find your first post about it, but the pics are gone. I have the valve and everything else all done, just need the vacuum line. Thanks,

Brew

 

Brew here 'tis----unabridged and complete, FWIW! Use what you can or want, ignore the rest.


This works very well---here’s my story with photos....

As a preface I’ll explain my cargo/work van has been equipped by me with a typical three speed blower that runs across a core much like the front, heated with hot coolant. A three-port hand operated diverting ball valve could direct coolant flow first through the rear heater, returning to the front heater core then back to the engine block or bypass the rear core altogether. As it turns out feeding the rear heater first didn’t affect or reduce front heater output at all when the rear blower isn’t running. IF both blowers are running simultaneously during initial start up it takes a little longer to heat each space. The front can be more quickly warmed by not running the rear blower at first then starting the rear after a comfortable temp is established up front. Using a thick vinyl curtain that’s not insulated helps divide the two temp zones making each heater a bit more efficient in its designated space. (This works equally well for the A/C up front----none in the rear. During the warmer months heat doesn’t escape into the rear partly because its located overhead in a raised roof bulkhead already heavily insulated. After discovering it wasn’t necessary to divert flow around the rear heater that valve was removed.

One more hand operated shut off ball valve had also been installed to isolate the front heater from hot coolant in order to lower vent leaving air temps (LAT) at the A/C vents—it did this very well. There was a down side because in Defrost mode or on cooler days warm air wasn’t available without opening this valve, not the most convenient thing to do being mounted under the hood. IMHO there had to be an easier way. Photos show these two valves before vacuum valve installation:


Enter now a vacuum off in-line valve from a ’76 Corvette (gasp—Chevy parts in a Ford???) pictured here along with a more common mushroom-shaped valve:


I liked the straight line flow as it seems a better idea over the turn in the flow path of the mushroom shaped valves. Its somewhat compact size & shape also perfect for an already-tight engine bay. (The valve used just might be a generic style, possibly used in many different applications, not necessarily found in only GM products. This particular style popped up in a search on eBay Motors, probably could be found most anywhere else too. The company 4 Seasons makes these valves, have a great selection of OEM and generic styles available, have part numbers that most parts outlets can cross over.

Having replaced the A/C compressor, line set and orifice tube recently I wanted the coldest air possible even on 90 plus days with high humidity. Placing the vacuum valve in the coolant hose feeding the front heater core and tying its operation to the Max A/C Recirculation servo tubing off the Function Control Connection Block I’d have all normal selections of the Function Control plus automatically stopping coolant flow to the front heater too. (The added vacuum line was eventually routed over top of the heater core case then exiting through an existing hole in the firewall that already accommodates one of the heater core connection tubes.)





Valve mounted for ease of maintenance if necessary. (Additional hoses are supply and return for rear heater.)

The result was a lowering of the LAT at the dash vents by the hoped-for 10. Best thing is now I don’t have to do anything more than move the Function Control switch to Max A/C!

Just another way of doing this---certainly not the only way I’m sure. Hope this is helpful to anyone else looking to try it for themselves.

I can be my own devil's advocate now in hindsight. The Max A/C function is recirculating cabin air so by design the blend door is completely closed when in that mode. Just a thought, saves a lot of work........

The only real problem with triggering the cold air mod via the heat/cool function vacuum/electrical switch is there's no "built in" way to have warm air defrost should that ever become necessary. Without use of a separate switch solely to activate full stop of coolant flow to the heater core there are a few minor downsides to this mod as its typically done.

Anyway feel free to PM me or post here again if I can help in any other way!

 

Thanks, i will go through it and see how yours compares to mine (being 7 years older) and see if I can hunt it down.

Brew

 

Ok, I hunted down a schematic and chart that says there is a white vacuum line from the hvac and it is the only one that has vacuum only on a/c max setting (and when off) I am going to see if I can find that white line and tie in to it. Will let everyone know if it works.

Brew

 

Check the top front of the dashboard, see if there isn't an access panel like mine---your tie-in lines might be there Brew!

 

Thanks I will do. I was hoping if I removed the dog house, they might be easy to get at too. I do not recall my dashboard having an access panel at all, but I haven't looked too close. We will get 'er done one way or the other, thanks for the help so far.

Brew

 

Ok, I just wanted to add what I figured out. I found the vacuum hose I was looking for, it was a white one down next to heater core. In my van, if you look down to the right of the heater core box, you will see a white vacuum line running to the actuator that opens and closes the recirc flapper. So the only time my coolant is bypassed is when I have max a/c on. It was easy to pull the vacuum line out and add a T.

I ran the new vacuum hose from this white line, through the fire wall where the lines to the heater core come in. Honestly not the best place, it was tight enough that it cut off the vacuum at first. I pulled the new hose around a little and it worked in to a place with more space and works fine now. I haven't had a chance to test the whole system yet, but I do know no hot air comes from the vents if I turn the temp control to hot with max a/c selected. I will see this week if it seems colder, or truck over heats, or anything like that. I was going to move the line to a more pinch resistant place, but it would be so easy to change out, I will just wait until I have a problem.

Brew

 

Thanks for the follow up Brew! It seems both our systems are similar with the Max Air setting.

 

Yup, it was pretty much exactly what you did, except I used the motorcraft bypass valve that had the 4 connectors. Same white hose and everything.

Thanks again for the write up, and the help.

Brew

 

At some point in the near future I'm going to refine this mod to allow stopping coolant flow separate from the A/C control---I notice I get just a bit of heat still even in the Vent mode regardless where the temp control is set.

I initially thought this was from a faulty temp control or blend door motor but its due the design rather than failing components.