Deice low pressure light

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catmando
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Deice low pressure light

Post by catmando » Tue Oct 29, 2019 1:32 pm

Proud new part owner of a DA42. Now that winter is approaching I have been trying out the deice. Seems to work just fine, but after a few minutes the deice pressure low annunciation on the g1000 comes on. I have run the check list and the issue persists.

On the ground with deice on all the appropriate surfaces weep. In flight it’s the wings also appear to be streaming small amounts of fluid.

Windshield deice works fine.

After leaving the pump on in flight the appropriate amount of fluid seems to have been used.

I am assuming it’s a sensor failure, but would like to know as much about how it works etc, before taking it to the mechanic.

Also note that the preflight checklist seems to expect this annunciation to come on??
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Re: Deice low pressure light

Post by ultraturtle » Tue Oct 29, 2019 11:35 pm

Take the toggle switch out of the test position. That will fix the problem. Not that I've done it (several times), but I know a guy who has...
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Re: Deice low pressure light

Post by OE-FYA » Thu Oct 31, 2019 11:29 am

I had the same thing in flight. De-ice liquid was 3/4 full .
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Re: Deice low pressure light

Post by catmando » Thu Oct 31, 2019 5:57 pm

I have had no way to test this theory, but I am hopeful that its because its actually too warm out. According to the manual you can expect the deice pressure light to be on, even in HIGH mode, if its warmer than 10 degrees C. If the tank is full, and the plane is in the hanger, its going to take a while for the fluid to cool below 10 degrees, if its only say 0 degrees OAT.

its pretty clear the fluid thickens as it gets colder, and at warm temps the fluid can too easily flow out the easiest point of exit, and not get evenly distributed.

That's the theory... awaiting a crisp fall day to give it a good test.
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Re: Deice low pressure light

Post by catmando » Thu Oct 31, 2019 6:00 pm

ultraturtle wrote:
Tue Oct 29, 2019 11:35 pm
Take the toggle switch out of the test position. That will fix the problem. Not that I've done it (several times), but I know a guy who has...
really?

My understanding is the test position has no real effect, except that it monitors the sensors (and so annunciators will light) even when the pumps are off.

Regardless very certain it was not in test, since this was at night, and I had the deice lights on, so I could watch the flow.
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Re: Deice low pressure light

Post by ultraturtle » Thu Oct 31, 2019 8:09 pm

catmando wrote:
Tue Oct 29, 2019 1:32 pm
Also note that the preflight checklist seems to expect this annunciation to come on??
That is correct. From 4.A.6.1 of the DA42NG Manual Supplement - Ice Protection System:
NOTE:
The ANNUN-TEST mode activates the DEICE LVL LO
caution immediately if the de-ice fluid quantity is low and the
DEIC PRES LO caution after 120 seconds.
The 3 position toggle switch itself is a bit counterintuitive, with the OFF position in the middle. The most likely time I inadvertently leave it in the TEST position is after using the wing ice inspection light, toggling the switch to the down (TEST) position rather than the middle (OFF) position.
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Re: Deice low pressure light

Post by jb642DA » Fri Nov 01, 2019 12:22 am

I "exercise" my TKS system about every 30 days so the system doesn't "dry up" (as recommended on Page 9-S03-76 of the AFM FIKI supplement ) until I see the wing getting "wet". I run it for about 5 minutes.

FIKI Supp Page 9-S03-76
To ensure that all system components are filled with fluid, operate the system at least once in a month.

Sometimes, I'll get the DEIC PRES LO caution during this system run. Going to high or Max for a short time will usually clear it. Look at the FIKI AFM supplement for the DA62, pages Page 9-S03-43 and 44 for more info on this.

Here's the "CAUTION" from the page 44 -
If at ambient temperature above 10°C (50°F) and below 20°C (68°F) DEIC PRES LO warning appears in HIGH mode switch to MAX mode to cancel the warning. Above 20°C (68°F) ambient temperature warning cancellation may not be possible.
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Re: Deice low pressure light

Post by rdrobson » Sat Nov 16, 2019 8:38 pm

My system responds just like John mentions above. I keep my aircraft in a heated hangar and I think that has a lot to do with the low pressure warnings. Switching to a higher flow setting seems to make it go out.

Also, if my system hasn't been run for awhile, I make sure to activate it long before I expect to hit any icing (like 5-10 minutes) so that it is ready to go when I need it.

--Ron
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Re: Deice low pressure light

Post by ultraturtle » Sat Nov 16, 2019 9:42 pm

ultraturtle wrote:
Thu Oct 31, 2019 8:09 pm
NOTE:
The ANNUN-TEST mode activates the DEICE LVL LO
caution immediately if the de-ice fluid quantity is low and the
DEIC PRES LO caution after 120 seconds.
The 3 position toggle switch itself is a bit counterintuitive, with the OFF position in the middle. The most likely time I inadvertently leave it in the TEST position is after using the wing ice inspection light, toggling the switch to the down (TEST) position rather than the middle (OFF) position.
Wording is a bit complex, but the point I was trying to make was that (skipping the intermediate clause), the manual reads:
The ANNUN-TEST mode activates ... the DEIC PRES LO caution after 120 seconds.
i.e. you will get a DEIC PRES LO caution two minutes after power up every time when the toggle switch is inadvertently left in the TEST position.

Also, you stated:
this was at night, and I had the deice lights on, so I could watch the flow
I assume that at some point during or after the flight, you turned the deice light off. It may be possible that you inadvertently placed the toggle in the lower (TEST) position rather than the middle (OFF) position when doing so. Not that I've ever made that mistake (several times), but again - I know a guy who has.

That said, pumps do fail. I had one go just outside of the two year warranty. It cost almost 1 AMU to replace.

Best way to avoid the expense is to exercise the system every month as the manual requires. Out of the hangar, since it makes a mess. Strongly recommend you exercise the windshield pumps airborne before flying through a rain shower - it is difficult to clean up the canopy afterwards, so every little bit helps.
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Re: Deice low pressure light

Post by jb642DA » Sat Nov 16, 2019 10:38 pm

The "DEIC PRES LO" caution message I've had is related to turning the DE-ICE SYSTEM on in flight.......the "other" switch was not in the "test" position at that time.

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