Dead battery, again ... locating parasitic draw

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I recently replaced my battery. After a really cold night out doors in Feb, my truck wouldn't start without a jump. In the weeks after that, it started more and more sluggishly every morning until it wouldn't hold a charge over night. So I put the biggest Optima Yellow Top (D34/78) in about a week ago. And everything seemed fine.

This morning, the battery is dead enough that absolutely nothing works. I jump it and check that I didn't leave anything on that I shouldn't have. Absolutely nothing looks out of order. But I noticed that I hade the front defrost switched on on the climate control since it was rainy and humid out last night when I was out. I rarely have this turned on and it occurred to me that on the cold day when my factory battery met it's demise a month ago, I had had the front defrost on too.

So I assume I've got some sort of parasitic draw and will take the H2 into the dealer in the very near future. And I'm sure it'll be there for weeks while they try to figure it out

But being curious is there some relay that's getting opened and maybe sticking open when you depress the front defrost setting on the climate control? Note this is the front defroster and not the rear defogger which would give me obvious candidates for bad relays. As far as I can tell there's not obvious relay on the front. Might it be the A/C COMP RELAY in the engine compartment fuse box?