Heat - weird issue turning on heat

[lothos]

This is for my girlfriend's 2004 Chevy Impala SS.

Yesterday she tried turning on the heat and nothing was blowing out of the vents, and we couldn't really hear anything turn on. We just left it alone and maybe 10 minutes later I tried it again. I turned it directly up to High and it started blowing... she said it sounded a little funny but I didn't really notice anything weird. She had the same thing this morning, wouldn't turn on so she turned it down and when she turned it on High again it started to blow hot air.

-Only turns on when you turn it to high first, then you can turn it down.

-it blows harder and softer by itself without turning the knob.

She did have the heater core replaced because it burst and leaked coolant all over her passenger carpet. Other than that I don't know of any prior problems or repairs.

I know it's not exactly a Cadillac, but I think the engines and interior are similar enough. Hope it's OK to ask here

[CoupeDTS]

This is for my girlfriend's 2004 Chevy Impala SS.

Yesterday she tried turning on the heat and nothing was blowing out of the vents, and we couldn't really hear anything turn on. We just left it alone and maybe 10 minutes later I tried it again. I turned it directly up to High and it started blowing... she said it sounded a little funny but I didn't really notice anything weird. She had the same thing this morning, wouldn't turn on so she turned it down and when she turned it on High again it started to blow hot air.

-Only turns on when you turn it to high first, then you can turn it down.

-it blows harder and softer by itself without turning the knob.

She did have the heater core replaced because it burst and leaked coolant all over her passenger carpet. Other than that I don't know of any prior problems or repairs.

I know it's not exactly a Cadillac, but I think the engines and interior are similar enough. Hope it's OK to ask here

On older cars Ive worked on if the heat blows low but not high or vice-versa then its the resistor. Its a cheap part on those cars. I dont know the electronics of newer cars. You could probably look up a wiring diagram on autozone.com or in a chiltons? To see what the power flows through before getting to the blower.

Also Im sure you notice that new cars if you set the temperature to anything except the extreme high or low temperatures it wont necessarily turn on. Like if its cold out and you set it to 85 it wont turn on because it knows its just going to blow cold air. So it waits to warm up. So that makes me think maybe you have a HVAC computer malfunction.

[Cadillac Jim]

If the HVAC is on Auto, the normal condition, it won't blow heat until the car warms up. Then, it selects vents and moves the temperature doors do deliver heat or A/C as appropriate for the AUTO condition (high for lots of degrees of interior temperature to heat/cool, low to maintain temperature, etc.). If this happens when the engine is hot, check the coolant level. If all of those bases are covered and you are still having the problem, check out the way the vacuum hoses are hooked up under the dash; they may have crossed them when putting everything back.

[lothos]

thanks for the replies

the HVAC was on defrost, or defrost/floor. I think it always blows in that position, but either way we were already on the highway and the car was warm enough by that point.

We can still vary how high or low the heater blows, but you have to turn it on full blast to get it to turn on first. So, you can blast it and then lower it to a reasonable level, but just turning it on low doesn't make anything happen.

The heater core was replaced a couple of months ago and the heat has worked perfectly this winter up until yesterday.

I will check the coolant level.

[lothos]

Here's a little more information:

It's the 2004 Impala SS with the 3.8 supercharged v6. I think they use these in some newer Caddy models.

The HVAC has dual climate control. The controls are a little more basic than my 95 STS. To turn the heater on higher or lower there is a round dial. To select floor, vents, defrost, there's another round dial. There's also two sliders that move up and down to control the split climate zones. We think that the heat turns on right away, she doesn't think it has the feature where it waits until the car is warm to spit out heat like my 95 STS does.

Around July the heater core broke, spilling coolant on the passenger floor. It was replaced. We live in Minnesota, and it's been cold for a couple of months now. She uses the heat a lot, and the problem just started last night.

There are two problems she's complaining about:

-the heat doesn't start blowing until you turn the round dial all the way to the highest setting. Then, you can lower it so it blows less air. If you try to turn it on by turning it to low or medium ranges then nothing happens.

-the blower seems to vary in intensity when left alone on one setting. It seems to blow harder, then lighter.

I'm going to check the coolant level for her tonight. I also have a multimeter, so I can measure wire outputs or relays or anything else that is suggested.

I know it's not a Caddy, but I'm hoping the Chevy is similar enough that you guys can help. I'm really at a loss here on how to diagnose the problem, so all help is very much appreciated.

Thanks guys

[Ranger]

Locate the blower and next time it does not turn on whack the blower with a screwdriver handle or such. See if that helps. That would indicate a failing blower motor.

[lothos]

Locate the blower and next time it does not turn on whack the blower with a screwdriver handle or such. See if that helps. That would indicate a failing blower motor.

thanks Ranger, I'll try that when I check her coolant level. I appreciate the help

[WarrenJ]

If a wiring drawing will help any you can find it here:

http://i7.photobucket.com/albums/y299/WBucket/2004_Impala_Blower_Control.gif

Regards,

Warren

[lothos]

If a wiring drawing will help any you can find it here:

http://i7.photobucke...wer_Control.gif

Regards,

Warren

thanks Warren