"New" Mk VIII - sorting AC, heating, passenger window, and radio!

B

Blaxmith

Registered
Hello gentlemen,

I have recently got another Mark VIII, and I need help troubleshooting my AC and heating. I dont think either work. The AC clutch doesnt engage when I turn on the AC. but it does turn on the radiator fan when I press Max AC. also the heater doesnt produce hot air. Im 99% sure the AC is fully charged, but it just isnt engaging. is it likely that I need a new AC compressor? and is that job sort of reserved for professional HVAC people?

and what about the heater?

likely culprits? I am doing research online to the best of my ability but there are a bunch of people trying to fix their Mk VIII HVAC system it appears, lol.
 
oops. its actually 97. I always do that lol.

anyways, today I decided to inspect my blend door. I dont think the actuator is broken, because when I wiggle the grey lever behind the glove box, the actuator arm wiggles as well. But, I'm sort of confused how to "open the door" to let heat in, as I've seen people suggest.
 
As far as the AC is concerned, there could be a myriad of reasons...
  • Open Fuse
  • Variable Load Control Module (VLCM)
  • Circuitry short/open
  • AC cycling switch
  • AC system discharged/low charge
  • AC control (EATC)
The fuses to check should be a 40A fuse, Power Distribution Box Fuse 43 under the hood and a 15A fuse, Junction Panel Fuse 34 inside the cabin. Check the owners manual for details on the fuse layout.

After the fuse check, the simplest test is to bypass the AC cycling switch. The switch is located on top of the accumulator, a canister looking device located next to the firewall on the passenger side of the engine compartment. There should be a 2 wire harness connector at the AC cycling switch. Basically to bypass the AC cycling switch you unplug the harness connector and temporarily jump across the two pins corresponding to the two wires. Technically, according to the service manual, this is connector C169, Circuit 1040(R/BK) and Circuit 198(DG/O). Once the jumper is in place, start the engine, press the MAX AC button and rotate the blower motor speed control fully up.

If the AC compressor clutch engages with the AC cycling switch bypassed, the system is either low on charge or you need a new AC cycling switch.

If the AC compressor clutch does NOT engage with the AC cycling switch bypassed, deeper diagnostics are in order, starting with checking for circuit shorts/opens and the VLCM, EATC and AC clutch along with the AC compressor and AC system state of charge.
 
Blaxmith said:
oops. its actually 97. I always do that lol.

anyways, today I decided to inspect my blend door. I dont think the actuator is broken, because when I wiggle the grey lever behind the glove box, the actuator arm wiggles as well. But, I'm sort of confused how to "open the door" to let heat in, as I've seen people suggest.
Click to expand...
It's usually the plastic black lever connected to the actuator that breaks, not the actuator itself. If you can move the grey lever that usually means the black lever is broken, or if it moves a little maybe the grey arm was modified by someone else (doubtful). Here's a video showing the operation of the blend doors with a modified metal grey arm.
 
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