2016 Peterbilt 587 Electrical problems

[Waterloo]

(03-15-2021 )Alexp86 Wrote:  Still trying to figure out the issue I'm having. I've spent a long time looking through wire cleaning grounds etc...

The biggest issue for me atm is the a/c defroster not working. When I click the snow flake to turn the cold air on or if I put it on defrost its popping the fuse.

I've unplugged the compressor and it still pops when I click that snowflake, so I unplugged the high and low pressure switch and it didint pop. If I plug 1 in it doesnt pop but with both switches plugged in it pops.
Does anyone know what could be causing this? I had a friend tell me it's the computer that will need to be replaced and I'll be looking at 5000+ is this true?

I would look at the blend door actuator, it will be up under the dash, passenger side, on the left side of the AC condenser box, toward the steering wheel side, there are normally two. Also, there is more than likely one under the hood at the firewall, up under the cowl on the right side of the AC condenser/box unit. I would start under the hood, that is the fresh air blend door actuator and is normally a different part number than what is under the dash. When you go to defrost, closing that fresh air blend door is the first one to go into action to cut off the fresh air coming into the cab. Does the AC have issues when you put it at MAX? Or only at defrost? If only defrost, I would suspect the interior unit, it will be the actuator at the top of your AC condenser box, a real PIA to get too, but it is doable. The screws they use to hold those in are torx heads, a ratchet able to hold a torx bit, or a torx bit socket, is the best tool to use to get these out. I want to say it is a size 15 torx bit, but not 100% sure on that.

My thinking, it is a wiring issue, rubbing up against something metal blowing the fuse. You will need to pull all of the plastic crap off of the dash from the floor up on the passenger side to get to it.

Here is a link to the blend door actuators, https://truckerac.com/heaterandactuators.html

Just a tip, if one blend door actuator fails under the dash, odds are the other is soon to follow, I always replace both when one fails. The one under the hood, I have never had to replace it, going on 1.2 million miles... The ones under the dash and sleeper, every couple of years they tend to fail. I normally carry a spare with me, as the dash and sleeper actuators are normally the same part number.