Hello All,

Long time admirer of the Maule and long time stalker of this forum. I've learned a lot from y'all and am now the proud owner of a 1998 M7-235C.

It is a low hour aircraft so having a few issues pop up but to be expected I suppose. Few it twice and is now in the shop for high oil temp (looks to be a faulty vernathurm) and a leaky aux pump (Weldon on the way).

While it is down with the cowl off I am gonna try to look at two minor issues myself.

Pax side cabin heat knob will not pull out.
Neither cabin ventilation knob will stay out. They pull out and give a nice blast of cool air but then (pilot side rapidly) and pax side (slowly but surely) close not quite fully but to about 1/4 open.

Heading out to the airport Monday with the new Vernathurm. While the A&P replaces that, what recommendations do y'all have for the heat and vent controls.

Thank you in advance
Cheers
Tim

78NC

The cabin heat and air controls are mostly a function of the metal slides with hoses attached on the firewall side. They should be clean and lubricated so the slide operates smoothly without binding. If one won't hold its position, squashing it slightly at the bend in the metal channel should fix it. Don't squash it too much or it will be hard to operate.

Also, a bend in the cable adds a little drag so they will stay in place a little better.

See, that’s why I love this forum. Both suggestions way less complicated and costly that ordering button lock controls. Thanks fellas!

Now I'm confused....Don't the cabin air and heat controls twist to lock in place? It seems mine twist clockwise to lock in position and counterclockwise to loosen so you can push in and out...

I haven't seen any cabin air/heat controls that lock but maybe there are some out there. I don't think the any of the stock ones from Maule do but someone who owns a new Maule might know better. I run with my controls all the way out or all the way in so I don't know if a locking knob would be much help.

The way these things work is very low-tech. The control pulls the metal slide with the hose up the channel. At the top of the pull the hose lines up with a matching hole in the firewall. When the slide is all the way down, the metal covers the hole in the firewall. If the crimped edges of the channel are too loose, then the slide with the hose will work its way down the channel due to weight and vibration in flight.

Locking would be nice but per Andy and gbarrier comments, not completely necessary. If Maule has a locking control on the newer models (mine is a 1998) I would consider it. Before the fellas came up with the simple fix I was looking at locking or ratcheting controls as a replacement option. All of the ones I could find all were for “uncertified aircraftâ€￾. Thus illegal for just climate control?

The factory original controls on my 1977 M5 all have a slight friction lock. Placarded on the knob to twist counterclockwise to release for adjustment.

I thought all Maules were that way. Remember a post from years ago (Jeremy?) that cautioned against adjusting without twisting or the friction in the knob housing would be worn away.

Kirk

That only twist-lock control I can think of in Maules is for the rudder. Like others have said, could be your plane was modified (or the factory had some option) for a twist lock control on the cabin air controls as well. Is it a “Tâ€￾ shaped handle?

I’m not sure if the cabin heat and cabin air cables are intended to be some sort of twist lock, but I have found that they tend to move much more easily if you give them a slight twist in one direction or the other. You’ll feel a springiness in the proper direction, and twisting it a few degrees that way seems to relieve a binding between the thick uppermost part of the inner cable and the housing. I’m not at my plane right now to check, but I think the might even be a groove along one side of that upper inner section; perhaps that engages with a raised area in the housing, and this is the source of that binding.

The cabin heat and fresh air controls can be friction locked if installed correctly
You will note that the metal shaft going into the panel ferrule has a groove in it which aligns with a tooth in the hole of the ferrule.
Turn the knob left or right slightly to relieve friction and if all is well at the valve on firewall, then the knob will slide in and out.
If there is no need to twist the knob a fraction, then it can vibrate in or out, though usually in.
The adjustment is to twist the ferrule in panel, or the wire at the firewall valve to cause a slight bind.

Thanks for the better explanation Jeremy. Never looked that close at mine. Original parts to 1977 and under my care for 15 years. So far so good, they still work!

Kirk

Many thanks for the advice. I did squash the channel on the slides and does seem to help. I also played with the knobs on the dash. It seems like mine stay in the “unlockedâ€￾ position but by twisting the knob I can cause it to “jamâ€￾ and hold position. This is the way it is designed correct? Looking forward to getting airborne this weekend and trying it out and hoping the oil temp issue is fixed!

drak, yes sounds like yours is as designed but needs adjustment at the ferrule as described by Jeremy. Never done the adjustment myself so can’t describe better than Jeremy’s post.

Kirk

Actually, the relationship between shaft/knob and ferrule should be set so there is friction, therefore when pulling in or out, the knob will need to be turned slightly to be able to move it in or out, and thus when letting go of knob the friction will keep the control in the position you have selected. Partially out or fully out.