I've heard on later models simply cutting it off restrict a vital flow of coolant, perhaps a factory bypass approach from a vehicle that is identical that offers it is good, but see it as costly and rather difficult as we are talking about a cramped area to work in, being a van.

 

What valve did you use?
Does it "bypass" the heater and connect to the other heater hose or just shut it off?

 

Jay when I get around to doing this mod I'll use an American made ball valve suitable for 5/8" ID hose---it will just stop flow altogether. It will be spliced into the line leading out of the T'stat housing heading to the heater core.

If there's concern of potential over heating a bypass type ball valve can be used to re-circulate the coolant back into the block, bypassing the heater core completely.

I installed a rear heat only core/blower in my cargo van and in order to get the most heat into the rear re-routed the coolant flow first through the rear core then to the front core. This was Tee'd into the existing heating system but I added a bypass valve allowing shut off of the rear core---was concerned coolant flow during warmer months would heat the cargo area. As it happens without the blower running there is no noticeable heating effect when flow is still present.

My next step will be to leave the rear system flowing all the time but install a shut off valve in place of the bypass valve. There is more than enough room for this mod once you remove the air cleaner canister--you'd be surprised just how much more room in fact.

 

Mine does not bypass, it just stops the flow all toghether.

 

It worked, I just got a "Ball valve". didn't feel the need to try to run a cable or switch in to the cab.
Still don't blow snow like my nissan, but a least it feels like it has A/C now.
I put a thermometer in the driver vent... 48 degrees. Driving, at 60mph with outside temp of 78.

 

I just completed this mod on my '00 E250 with 5.4 gas motor-----used a vacuum operated valve instead of hand operated. In fact I previously had a diverter valve for a DIY rear heater along with another valve to completely stop coolant flow to both heater cores.

If anyone is interested I've written a "how I did it....." thing complete with photos---glad to post it here if it would be helpful.

 

As I've been thinking of doing this myself I would like to see your pictorial. TIA

 

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.

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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:
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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:
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I liked the straight line flow as it seems a better idea over the 90° 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.

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.)
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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!<O</O
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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.<O</O

 

JWA - nice pictorial - where did that vacuum diagram come from? I think I'll add an electrically operated vacuum switch in the added vacuum line from the Max AC line so I'll cut off the water flow to the core only when I need the extra cooling. It will be like an extra setting - Max AC and then Super Max AC.

 

DT that diagram is from my Ford EVTM CD-ROM but those are available in a book form, found on eBay according to your trucks year and model. Its quite a valuable publication to have if you're doing any sort of refitting or repairing of your electrical or vacuum opertated controls.

My system is set up pretty much like you describe because in Max A/C not only am I recirculating cabin air coolant flow to the front core is also cut off. In Max A/C lower temps at the vents is possible because air flow isn't directed over the core. There are electically operated vacuum valves that would open or close something like my heater valve you might incorportate. Take a look at this site: http://www.mtgparts.com Originally I obtained some parts for this mod but decided to refine my idea to its existing layout. MTG has some great stuff for your ideas.

Thanks again!