1966 M20E Pitot Heat Problem

[Matt Ward]

I'm the proud new owner of a 1966 M20E, my first plane!  So far so good except for one issue I'm hoping you all can offer some insight on.  During the pre-buy inspection, the pitot tube wouldn't heat up.  The switch doesn't appear to be tripping, no fuse appears to be blowing, it just doesn't get hot.   At the inspection, the A&P pulled the access plate, disconnected the wires & reconnected them (I think) and suddenly it heated up perfectly!  The entire fix took less than five minutes.  After flying the plane for about 10 hours since, it's back to not working.  Before I take it to my new mechanic, I was wondering if you guys might have any leads on what the problem is.  Thanks for anything!

-Matt

[cliffy]

Start where  you had success before   Pull the panel and try to find the loose wiring or you may have to pull the probe itself 

Your mech can also do a good resistance check right from the leads in the wing panel. 

OH congrats on finding your airplane

Edited April 12, 2020 by cliffy

[carusoam]

Welcome aboard Matt.

Ms is pretty good about solving problems...

Hang out for a while too...  
 

While you’re hanging out...

Make a list of tools you want to have...

I’ll start it for you...

1) Multi-meter.  Used for testing things like...

• Battery voltage... need to have some volts...
• Switch... need to not have any resistance... if it does, flip the switch...
• wires... again, no resistance is good.
• Resitor... a pilot heater is a big resistor...
• Ground wire... must be attached to ground... or the rest of the plane...

2) Contact cleaner. Used for cleaning the things that connect the other things in this list together...

3) Patience...

• the ability to watch when somebody fixes your plane...
• so you know what to look for the next time...
• when it repeats itself.

PP thoughts only, not a mechanic...

Best regards,

-a-

[Matt Ward]

Thanks for the reply!  To be clear, the A&P pulled the access cover at the actual pitot tube - not in the panel.  I didn't think that was something an owner could do but maybe I'm just not familiar enough with the FAR yet on that.  

[carusoam]

There is a list of about 23 things that you can do as an owner of your own airplane...

and some quirky things you are not allowed to do...

And if you don’t have a multi-meter or know how to use one... there are things on the list you may be better not touching...

Realistically, we just described the pitot heater as if it  was simple as a light bulb.... 

In the end they are both electrical resistors that heat up when voltage is switched on...

Changing it out probably requires a mechanic... testing it to see what is working and not working isn’t as complex...

Look up owner maintenance... you will find the list.

Best regards,

-a-

[Mooneymite]

7 minutes ago, Matt Ward said:

Thanks for the reply!  To be clear, the A&P pulled the access cover at the actual pitot tube - not in the panel.  I didn't think that was something an owner could do but maybe I'm just not familiar enough with the FAR yet on that.  

As an owner, you can "pull" most anything you want.  The trick is putting it back together and returning it to airworthy status.    That's a job for the certified professional.

The ubiquitous hangar elves can sometimes intervene since none of them have ever seen a logbook.  

Edited April 12, 2020 by Mooneymite

[Guest]

1 hour ago, Matt Ward said:

I'm the proud new owner of a 1966 M20E, my first plane!  So far so good except for one issue I'm hoping you all can offer some insight on.  During the pre-buy inspection, the pitot tube wouldn't heat up.  The switch doesn't appear to be tripping, no fuse appears to be blowing, it just doesn't get hot.   At the inspection, the A&P pulled the access plate, disconnected the wires & reconnected them (I think) and suddenly it heated up perfectly!  The entire fix took less than five minutes.  After flying the plane for about 10 hours since, it's back to not working.  Before I take it to my new mechanic, I was wondering if you guys might have any leads on what the problem is.  Thanks for anything!

-Matt

The pitot heater is as simple as it gets, if you can plug in an extension cord you can handle this. as long as you don’t disconnect the pitot line to the ASI you should be fine.

 The pitot head has two male pins and the plug has two female pins, it’s possible that either is worn and loose causing intermittent operation, you might also look at the wires on the back of the switch.

Clarence

 

Edited April 12, 2020 by M20Doc

[Ross Taylor]

And...photos and details on the new plane!  We also have a '66 E (s/n 1078) and love it.  It's a great fit for us.

[carusoam]

@Matt Ward Matt,

if you are checking in,  M20Doc set you up with some excellent details...

Best regards,

-a-

[Matt Ward]

You guys are amazing! Now I just need the snow to stop so I can get out to it. 
I am #994, BTW. 
Thanks for all this and I’ll let you know what I find. 

[Matt Ward]

Here is the culprit. Hopefully we can solder it. 
 

[carusoam]

Great follow-up so far, Matt...

I am not familiar with that part...

But if that is the heater... solder probably isn’t the best fix for it...  

Expect that some specialized high temp solder may be the right material for it...

https://partaviation.com/39a3639

There may be a whole bunch of used ones available around here if you need to look for one...

Best regards,

-a-

 

[Paul_Havelka]

I wouldn't solder that.  You can see that the wire has been arcing across and burnt some of the conductor away.  Hopefully there is enough wire for you to cut the end off, strip back the necessary amount and reattach if possible.  It appears that the screw, flat head, can be removed and should give you access to the internals.  Pics of that would be helpful.   As far as removing the access panel to troubleshoot that I would not consider that to be an operation that required an A&P but the fix is possibly a different story.  I wouldn't say it is a complex system/assembly but every person interprets the FARS just a little differently.  Best thing to do is ask your mechanic what he thinks.  I'm lucky enough that my mechanic trusts me and my work and I just fill him in on whatever work I'm doing and he may or may not pop his head in the hangar if we're both there at the same time just to see if I need anything.  When I'm done I tell him all that I did and he prints me off a shiny new sticker to put in the logbook.

[Guest]

10 hours ago, Matt Ward said:

Here is the culprit. Hopefully we can solder it. 
 

The screw holds the 2 halves together, undo it, open the 2 halve to expose the pin. Strip some fresh wire, flux and solder.

Clarence

[Matt Ward]

Thanks a lot, Clarence.  I'll have my A&P do that and hopefully check this one off the list!