Strange intermittent blower problem

2001 XJ Sport, I've owned it for a couple years now. Occasionally, upon startup the blower will fail to come on at all, regardless of HVAC control setting. It will, after varying lengths of time, begin working as normal. I can't seem to wiggle any particular component inside the cabin to coerce it to begin working although it does occasionally seem to come alive over a sharp bump. I've had the center stack apart a number of times and the HVAC harness looks perfectly intact and the connectors aren't melted. Does this system have a relay in it somewhere I'm not aware of? My old XJ was an '88, so most of my service info is slightly outdated.

Before I go tearing the Jeep apart, has anybody had this issue before? After a quick google search I came up empty handed for XJ related issues.

TIA.

I suppose that the most likely problem is a burnt commutator segment in the blower motor. Seems like it's easy to pull the blower out. You might be able to take the blower apart and polish the commutator segments where the brushes ride. It's like roulette or Wheel of Fortune. If it stops on the burnt segment, it won't get power to the armature until it shakes off the burnt spot.

Another test when it won't work is to try jumping the motor directly from the battery with wires. If it still won't work, it's gotta be the blower motor.

Here's a couple things to do.

Refer to the attached pics.

Place the AC/Heat mode selector switch to OFF "O".



Roll the glove box down and look inside.

In the pic, the black relay is the blower relay.



Look inside the HVAC area through the glove box opening, to the right of the blower relay. You'll see the Recirc Air Door.



If the door is open you can see the bottom of the blower fan. If the door is closed, start the engine to charge the HVAC vacuum system then shut it down. Leave the key in the RUN position. Move the fan speed selector to #1 position. Move the mode selector to MAX AIR (Recirc), #11 position. The door will open. You should see the blower fan turning.

Shock therapy, like hitting a bump in the road: If the fan is not turning, tap the top of the blower relay with a screwdriver handle to see if it starts. If not, hit the bottom of the HVAC unit below the fan with the palm of your hand and see if it turns.

If tapping the relay starts the fan, replace the relay. If pounding the bottom of the HVAC Unit starts the fan, replace the blower assembly.

If you have juice going to the blower motor plug (test light or voltmeter) and the motor won't run, it's the motor.

Intermittent symptom diagnosis is a drag. Well, I changed the relay since its easy to get to and I have multiple spares. It's still acting up, and a swift tap on the bottom of the HVAC housing makes it come on consistently. Looks like I'll be picking up a new blower motor. Thanks for the help guys!