Air Conditioning Alternator Field Excitation Battery Location?

[ultraturtle]

Not getting power from the dedicated alternator on the left engine to the air conditioning system. Control panel can be powered by external power, but getting nothing from the alternator. Current limiter is intact, blue regulator box does not display red fault light. While I cannot find a maintenance manual or even a wiring diagram online, I have been told that there is an alternator field excitation battery located somewhere, but where? My mechanic and I have been told to check under the right front seat and in the air conditioning equipment bay behind the aft bulkhead, but no luck so far. Can anyone help?

[rdrobson]

I have no idea if this is similar or not, but after I took delivery of my DA62 I found that the a/c did not work. The control panel lit up, but no cold air came out of the vents. My mechanic talked to Diamond and found a circuit breaker back by the air conditioner aft of the rear seats. (I assume this is where the DA42 a/c unit is?) The breaker was not listed on any wiring diagram I had and was not a user accessible item. The good news is that once they reset it, it has worked perfectly.

--Ron

[ultraturtle]

Probably similar. There are 5 breakers back there. None tripped. They are not the problem in this case. Thanks, though.

[ultraturtle]

Problem solved. The excitation batteries (2) are cleverly hidden below the storage bin behind the left rear seat (red arrow):

A skilled and dextrous mechanic can swap them out without removing the rear seat by removing the rearmost bolts (circled in blue) of the thin and flexible fiberglass cover, bending it up a bit, and working by feel.

This is unique to the DA42-VI. From what I understand, the batteries are clearly visible on the air conditioning equipment rack behind the rear bulkhead on the DA62.

Sadly, there is no maintenance guidance from Diamond Aircraft to replace these batteries on a scheduled basis as yet. Mine went completely dead less than 3 years after aircraft manufacture date, so I would suggest folks with the air conditioning option replace the alternator field excitation batteries every 2 years until we receive some sort of guidance from Diamond.

This is the replacement battery. You need 2:

[Karl]

Problem solved. The excitation batteries (2) are cleverly hidden below the storage bin behind the left rear seat (red arrow):

AC Alternator Field Excitation Batteries.jpg
A skilled and dextrous mechanic can swap them out without removing the rear seat by removing the rearmost bolts (circled in blue) of the thin and flexible fiberglass cover, bending it up a bit, and working by feel.

This is unique to the DA42-VI. From what I understand, the batteries are clearly visible on the air conditioning equipment rack behind the rear bulkhead on the DA62.

Sadly, there is no maintenance guidance from Diamond Aircraft to replace these batteries on a scheduled basis as yet. Mine went completely dead less than 3 years after aircraft manufacture date, so I would suggest folks with the air conditioning option replace the alternator field excitation batteries every 2 years until we receive some sort of guidance from Diamond.

This is the replacement battery. You need 2:

AC Alternator Field Excitation Battery.jpg

I suspect the reason for not having a recommended replacement time is due to the fact that loss of Aircon is not an airworthiness issue. As soon as Diamond give direction on the recommended replacement times then you have to change it if it needs it or not.

[CFIDave]

Interesting. I never had any problem with the excitation battery for the air conditioning in my DA42-VI, nor did I ever replace it during the 4 years I owned the aircraft. But I appreciate your research into finding it.

[ultraturtle]

Update:

It just dawned on me that the batteries were not the problem, and probably do not need to be replaced on a frequent basis. The problem was buffoonery on my part.

Again, no wiring diagram or other documentation I can find to verify it, but I am fairly certain that the air conditioner "Aux Power" switch closes the circuit from the excitation batteries to the alternator field. I left this switch on between flights which drained the batteries. They could probably have been recharged with a 24 V charger connected to the battery side of the voltage regulator (blue box mounted on the wingtip side of the left engine) rather than being replaced.

They are sealed lead acid batteries, which usually last only 5 years or so. The first DA42s with factory air are coming up on that time frame. When the batteries fail, the air conditioning control panel receives no power from the alternator, but will power up from external power. When faced with these symptoms, check voltage and replace the batteries as necessary.

Hope this helps save someone a month or so tracking down the cause of a failed air conditioning system.