The rear blower comes on as soon as I turn on the front HVAC system on my 2012 E350, even if the blower switch is set to off. It also only blows at medium and high speeds. Basically the off and low positions for the rear blower don't do anything. Is it the switch, resistor, or something else?

 

It could be either as your described symptoms are frequent problems from those components. Hoping its the switch because if its the resistor and this is factory A/C you'll have to access the blower motor etc housing behind the interior trim.

Good luck with this-------please let us know what you discover.

 

+1 for the switch being faulty, but
I'd make sure some yoyo didn't run a wire or shove a pin through a couple of wires to connect them
Good luck

 

Ordered a switch, will update everyone as soon as I get it in.

There was some yoyo working on the van before I bought it. He cracked the A/C evaporator box, didn't reinstall the recirc/fresh flapper and solenoid as well as the fresh air duct on top of the evap box. I couldn't even drive it without keeping the windows open due to the exhaust fumes coming in.

 

You’re talking about the front evaporator?

Sixto
07 E350 5.4 108K miles

 

Someone messed with the front A/C system and caused all sorts of destruction. The top of the evaporator enclosure was missing the duct so instead of fresh air there was exhaust infused air coming in.

Grate missing the flap and solenoid

Top of evap housing covered with cardboard and held down with rolled microfibers

 

Well, you have a bit of work ahead putting that all back together correctly

 

Working on reassembly today while waiting for the blower switch. Got everything almost buttoned up, but the new accumulator has a kink in the flex section of the line going to the evaporator. Turns out the line coming from the accumulator was a little too long. This was a GPD 1411886 ordered from RockAuto. Started a return on the GPD and bit the bullet on an original Motorcraft part. For 2.5 times the price of the GPD, it better fit correctly.

No HVAC box. Pretty large opening!

Mostly reassembled.

 

Looks like a bit of wreck damage on that RF fender might have broken the original HVAC case?
Looks like you are well on your way back together
I get most of my AC parts these days from 1800 radiator
They sell me kits cheap, and have accumulators cheap too, but probably would sell you the same wrong one you got
But
They would be able to provide the other style that would work for you most likely
Ford parts are always the best IMO
Had a friend the other day that wanted me to use all GM parts to tune up his 1996 Camaro
Cost 500 for the parts IIRR over the chev dealer parts counter
They wanted 114 for a cap and 50 for a rotor or some ungodly amount

 

You've got a good eye for damage! Although I have no proof of the van being in an accident, I did see a quite a bit of overspray around there which makes it highly likely it was hit on that side. I snapped a pic of the original accumulator and the incompatible aftermarket one. You can see the overspray on the original.

 

Replaced the switch yesterday. No difference. Guess I'll have to replace the resistor. I'm really looking forward to removing the seats and tearing out the panels...