Ice Detection

[trev130eng]

Hi Guy's, got a problem with the ice detection system i can't seem to resolve. The fault is that during taxi the system on light is coming on and will not go off by putting the master switch to reset. The light will go off by pushing the light out button. During testing on EGR the following is happening. #2 system is testing ok, but after testing #3 the no ice light comes on after about 5 secs. I've changed ice detectors, ice interpreters and a couple of suspect diodes but i still have the same fault. (Spare parts are very suspect here though.) Every time i try and work my way through the troubleshooting guide i get different results every time i carry out the same tests. Two things i have noticed. After putting the switch to test, you are meant to intermittantly put the master to auto and reset for 10 secs with the on light going off and on and then staying on. The light is going off at first reset and then staying on no matter how many times i go back to reset. The other thing is that except for the above fault #2 system is testing fine but the no ice light is coming on within 5 secs during testing #3. If i then try to test either system the on and no ice light come on immediately i put the switch to test. Wait a few minutes and then i'm back to the original problem. Any ideas would be most appreciated. We have mechanical ice detectors.

[NATOPS1]

Try testing #3 first.... see if you have the same issue.

Its a heated relay... 90 sec (right) cant remember the flow. will have to check out the wiring... Heats up to turn on the No Ice light. If its stuck it (no ice relay I think) will be hot and the no ice light will stay on. Wait it cools and you can start over.

[tenten]

What about Auto De-icing Reset Relay (k50k) on cargo comp.

[NATOPS1]

The fault is that during taxi the system on light is coming on and will not go off by putting the master switch to reset.

(This sounds like the auto reset relay but later on in your post it (auto reset relay) seems to be working)

(try taxi with the LH or RH Ice det CBer pulled (or IGN Control CB) to see if you can isolate one of the detector circuits) (mechanical probes activate often for no reason)

The light will go off by pushing the light out button.

(Normal function, system is still "testing/ detecting ice" just no amber ice light)

#2 system is testing ok,

(meaning when you go to reset the ice light goes out... auto reset relay good)

Try and test 3 first... my guess is it will also test good...

but after testing #3 the no ice light comes on after about 5 secs.

(This points to the pulsing relay [my guess] or the 90 sec delay relay)

(Test 3 first and see if the no ice light comes on within 5 sec on #2)

The light is going off at first reset and then staying on no matter how many times i go back to reset.

(This is the puzzle)(light is the amber ice light yes?) or the no ice light?

If i then try to test either system the on and no ice light come on immediately i put the switch to test.

(The 90 sec thermal relay is HOT so the no ice light will illuminate, I think you have a pulsing relay issue stuck on always heating the 90 sec relay or the thermal setting on the 90 sec relay is bad.)

Good luck...

[trev130eng]

Asked them to fly with R/H ice detecter CB pulled.

[trev130eng]

Even though #2 is testing good i'm thinking why the amber light is not going on and off during the test and will not reset when the system on light comes on. Pulsing Or Hold Relay?

[NATOPS1]

Pulsing relay... For the NO ICE LIGHT on within 5 sec of testing #3.

It controls the cycling of the 28 VDC that heats up the 90 Sec delay relay, which illuminates your no ice light.

You can also check to make sure your interpreters are "cycling" and your diodes are good by checking the voltage on the coil X2 of the pulsing relay.

(both systems use the same pulsing relay)

Test #3 first and see if the No Ice light does the same thing "illuminates within 5 sec of testing the second detector"