Hey guys, I'm new to the forum, my name is Jesse and I just got a 94 marquis handed down to me from a friend. I just got her home today and realized every time you turn the ignition to the on posistion there is a strange hum coming from the front of the car. I know it's not the fuel pump because it came from the front, and also the last time it did it, it made a pretty bad vibration that shook the whole dashboard and scared the heck out of me. Does anyone know what on earth this could be?

 

Anyone?

 

no one has any input on this?

 

nope... no clue here. with the engine off and key on, I wouldn't think there would be any noise other than clicks of relays. The only thing I can think of that it could possibly be is something in the AC ducts that's messed up. But without being able to give a listen myself, I'm pretty lost on it. Oh, and generally give a day or two for responses as real life sometimes hampers abilities to respond promptly.

 

i know sorry about that i was mostly just trying to bump this so people would see it, I'm thinking it has soemthing to do with the ducts because my heater is also messin with me as well. the fan doesn't come on on any setting but the highest one and I'm getting a loud clicking from udner the dash it's very strange. Also the fan won't come on at all on the floor setting i have no idea what is going on with this thing

 

in that case, it's definitely in the ducts. you have multiple problems. sounds like the control module may be gone and the fan control module (resistor pack) is definitely shot. That one can be found in the ducting (either behind the glove box just to the driver side of the heater core area or on the firewall under the hood just to the driver side of the heater core. I don't know what year they switch from the outside to the inside. That one will fix the fan speed thing. you may also have a shot blend door and/or blend door actuator.

you may also have a few blown actuators on the vents or a loose/broken vacuum line under the hood going to the vacuum lines on the AC system (comes off a check valve just about on the center of the firewall if I remember right)

 

Another thought - Does the vehicle have airlift on the rear supension? If so, some GM models had the air lift air pump located under the driver side floor board. Depending on age, it made a very loud noise and vibration when the ignition switch was turned on and pumped up the airlift bags. When the vehicle levels the pump shuts off. If you don't know whether you have air lift, look in the trunk for a airlift shutoff switch on the trunk left side wall. There is also a fuel shutoff switch in the same vicinty.
Obviously though this wouldn't affect the HVAC and wouldn't vibrate the dash.

 

the one noise is a compressor for the air lift i had no idea these cars were equipped with that, the fan relay switch has been replaced and now that works, however the floor setting still has no function and a loud tick tick tick is still coming from the dash when the heat is on im lost

 

yeah... I'm stumped. unless there's a vacuum actuator and/or electric actuator that messed up, I can't fathom what it might be.

 

Hi, it's the air pump, comes on to lift the rear and you my hear it release air when the car is on or off.