heater / electrical draw?

[ryandrews123]

So when I turn my heater on my voltage drops low enough to dim my lights. I also have this weird sound in my engine bay on the passenger side that sounds like something clicking on for a few seconds then off. the sound from the engine bay has all ways been there, but obviously theres a new problem with my heater shorting out. Any body else have a problem like this, where i might be able to start looking? my truck is a 94 350 z71 rcsb. thanks

 

[woody31]

you need to isolate the noise,,your description is a little brief,,have someone cycle the key while you look underhood for the source of the noise,,put a dmm inline with your blower motor to check the draw ,,,

 

[ryandrews123]

So i found that the sound from the engine bay is my ac compressor its the medal plate clicking in and out. It does this whenever my heater is on. Is it suppose to do that? How would i go about checking the draw? electrical is not my strong side but i am defiantly wiling to learn thanks

 

[great white]

So i found that the sound from the engine bay is my ac compressor its the medal plate clicking in and out. It does this whenever my heater is on. Is it suppose to do that? How would i go about checking the draw? electrical is not my strong side but i am defiantly wiling to learn thanks

Nope.

But the compressor will come on if you have the AC button in or you have any of the defrost/defog modes on the HVAC head. If you put the selector to "floor" it should stop.

If it's clicking on and off it's because the refrigerant charge is most likely gone/low. The HT6 compressors on these trucks are notorious for leaking from the middle joint in the compressor housing.

AC shops even have their own nickname for them: "belly leakers".

The heater motor is a large amperage draw compared to other components. Make sure the grounds are good and clean, this will increase draw if they are corroded. It doesn't take much to spike the draw.

Does the same thing happen when you turn on other high draw components? Things like headlights, rear defrost, etc? If it does, it could indicate a weak charging system. Corroded battery cables, weak batteries, poor grounds, etc....

I wouldn't use a DMM on a heater circuit unless it was capable of sustaining a 25A load. That's the fuse on the blower motor circuit and it could very well spike that on startup. Not many of the "cheapies" can handle much more than 5A-10A.

My relatively expensive DMM (BK Precision) is only capable of 20A. I use a current clamp for higher amperages, but that's usually up around the alternator output amperages. 25A is kind of an in-between range for my equipment I don't really deal with....

 

[ryandrews123]

i have a new battery and alt and I upgraded/cleaned all my grounds a couple weeks ago. This problem only happens when my heater is on.

 

[woody31]

good point gw on the amp capacity,,,i use cen-tech d 266,,,not every one has a clamp style,,
it could be a blower motor going bad?? do you have a buddy with a similar truck,,maybe you could swap one out for a test,,new ones are about 25 bucks at my local orielly auto parts,,,hope you get it sorted out.

 

[ryandrews123]

even better ill just go pull the one off my 92 suburban and test it.

 

[ryandrews123]

so i pulled both blower motors and bench tested both with same results, both run fine. even tho my blower motor runs fine could it still cause a draw in my power? I'm going to install the suburban blower motor in my truck and see if I still have the problem.

 

[ryandrews123]

So I swapped blower motor, didn't fix my issue. also when the voltage drop occurs my oil pressure gauge drops and fluctuates and my rps fluctuate as well.

 

[steampunk1375]

You could try unplugging the AC compressor an see if the noise/voltage drop goes away. That would isolate the AC clutch out of the equation.