heater valve inop?

cessnadriver · #1 03-20-21, 08:58 AM

Hello all. My '65 C337 pilot's side heater vent is not working properly. When I turn the heater knob to the 12 o'clock position the knob turns, all by itself, to FULL (While in the air). I temporarily fix it by grinding the knob around the circumference and added a screw. I've looked at the parts manual and checked my "parts bird" but can't see how the cable and valve assembly works? I'm thinking that the return spring, mounted around the shaft of the valve, is broken? I haven't removed the battery and the box to get a real good look at the valve. Just looked up through the left side cowl flap. Any body got a clue??
Thanks, BILLS
PS: With the battery on that side I do see a lot of battery acid corrosion in and around the heater valve!!

TomM · #2 03-22-21, 03:15 PM

I have the same controls and when mine was doing that, the cable was binding which would spring the knob back. We lubed the cables and that fixed it. Mine was also on the pilot side......

If you look near the rudder pedals, you will see where the cable goes as the divider box is on the inside of the firewall.

Its just one of those chincy solid metal wire in a spiral wound metal outer housing and I do not believe there is a liner in there at all. So when you get some corrosion along with no movement, it sticks. Basically the same cable as the throttle on a lawn mower.........except with a much higher price tag.

After rereading your post, yours does the opposite of mine....It would snap closed again due to binding. Still may be the cable though

cessnadriver · #3 03-22-21, 05:29 PM

Tom M.
Thanks for the reply. I'll check the cable running to the diverter. At first I thought you misunderstood my post, but I see you caught my meaning. Yes my knob continue to the FULL position if the knob is at the 12 o'clock, or more position??
Regards.
BILLS
PS. Did you buy your orange Skymaster from "Skymaster Center" in S.C.? If so I looked at that one before buying local.

TomM · #4 03-22-21, 09:24 PM

Hey there Bill.

So my follow up question to you is does it spring from the mid point to full hot when you are sitting or just when you are flying? If you look at the mechanics one would think that with the cable friction as well as the knob/gear (in the back of the knob there is a gear which turns another gear which moves the cable) friction that it would not move all by itself. If it only does it when you are flying, maybe it is ram air pushing it??

Yes I did....not the best experience I have had. Was disappointed that I ended up doing more work trying to get the seller to sell the thing than the broker did. But that is a story for another time.

cessnadriver · #5 03-23-21, 05:13 PM

Tom M.
Yes while flying and yes I think it's something to do with ram air? I did check the gears on the heater knob. It maybe that I loosened up that knob right after buying the plane, while doing the initial Annual I found the knob would not rotate so I lubed it up with a spray grease. Sorry to hear your problems with your purchase!
Regards.
\BILLS