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Comment by Robert Stacey on June 14, 2014 at 2:08pm

I had the same problem but when I rotate the knobs they seemed to slide smoothly.( I have 2)  Let go and they stay where there at. Sort of like a throttle lock. 

Must have something to do with the bends in the push pull cable.

Comment by Doug MacDonald on June 14, 2014 at 11:18am

I used the all stainless carb heat box from AS&S but still had the issue with the cable not working well because the arm works in the opposite direction to what is desired.  First, make sure it is a good quality cable you are using and not the hardware/auto parts store variety (ask me how I know this).  The better push/pull cables from AS&S are Teflon lined and work much better than the cheap ones.  Secondly, I added a couple springs to help pull the heater valve into the final seated position; either open or closed.  My 701 installation is not perfect but it does work for the most part.

On a CH-750 I built with a friend, we mounted the heater box with the arm horizontal above the firewall shelf and brought the cable in from the side.  This setup worked much better than the setup on my 701.  We braced the cable to the shelf and the heater box works well in both the on and off positions.  We don't get much heat from the system due to the poor design of the heat collection muff but that is another story.

Unfortunately, I'm travelling for work and can't get at either installation to take a picture for you.

One other option you might consider for controlling the heater valve is an electric actuator.  I purchased one at Oshkosh last year (from TCW I think).  I'd planned on installing the actuator on my 701 but due to the existing installation being kind of jammed into a corner, I decided to save the kit for use on the scratch-built Cruzer I am presently starting.

One thing to keep in mind is that the construction of a heater valve is important to keep fire out of the cockpit.  I'm not certain if the Zenith supplied valve is entirely Stainless or not but my inspector insists on 100% stainless heat boxes (mandatory here in Canada).  An aluminum flapper valve will melt in the event of a fire and then your heater system will become a blow torch into the cabin.  Not a good day if a firewall forward fire ever were to occur but even more dangerous if the fire is able to enter the cabin.  These heater boxes are a critical safety device and need to be constructed accordingly.

As for James' suggestion of using a PVC valve, an interesting idea but poor choice of material.  Avoid the use of PVC in aircraft, especially in systems which can be exposed to heat.  Melting PVC gasses off toxic fumes which can incapacitate a pilot in an enclosed area like a cockpit.  This is why PVC insulated wires are avoided in aircraft despite the added expense of Tefzel wire.  Spending the few extra dollars on aircraft grade materials may seem like overkill in a small homebuilt like the Zenith products but these material standards have been developed over the years based on fatalities and thus should not be rejected without careful consideration as to why the standards exist in the first place.

Sorry to come across so preachy.  I hope this information is of use.

Doug M

Comment by James R Depfer Sr. on June 13, 2014 at 8:54am

I'm not familiar with the cabin heat on the 701, but I have the cabin heat option offered from Zenith on my 750. I had troubles trying to get the rotating flap on the heater working with the push/pull wire from my control. I finally gave up and installed a 2" waste-valve (PVC) for a swimming pool I got at Ace Hardware, although I'm sure its available at a swimming pool supply store. The valve's on/off action is push/pull that matches my wire. Had to make a few modifications to the valve handle, but that was easy. The valve fit in the firewall tube from the Zenith kit, so no real modification there. Although I want to make further modifications, I presently have a 90 degree PVC fitting on the cabin side to direct most heat to passenger side. Drilled a few holes in the 90 to allow a little heat to go directly toward me. I've seen a similar metal design in the past but couldn't find it right now. The PVC valve is a little larger and bulkier than I prefer, but does work good. I'm going on vacation in a few minutes, but if you want any photos, I could take a few in a week, plus a few days.