[shan1289]

Sometimes, whenever my HVAC turns on to cool or heat, it makes a loud, deep thumping noise when it first turns on.

It almost seems like it's trying to start up, but getting stuck, making this thumping noise and stopping briefly. So, the air blows, thump, stop, air blows, thump etc but eventually (after maybe 5-10 of these cycles) it runs normally.

Any idea what it could be?

 

[jreagan]

Have you tried just turning the fan on without asking for heat/cool?

 

[user_12345a]

is the indoor blower belt driven?

 

[supers05]

You have a heat pump?

Do you know how to check a capacitor? (You'd need a meter specifically for it) You comfortable with electricity?

My guess is that either, the run cap is half dead and/or the compressor is getting stiff. If the cap checks out good, then a hard start kit is the next option.

Cheers!

 

[shan1289]

Have you tried just turning the fan on without asking for heat/cool?

Yes, I actually just did that, and the problem still occurs. What does this tell me?

 

[shan1289]

is the indoor blower belt driven?

I have no clue. How would I be able to check this/find this out?

 

[shan1289]

You have a heat pump?

Do you know how to check a capacitor? (You'd need a meter specifically for it) You comfortable with electricity?

My guess is that either, the run cap is half dead and/or the compressor is getting stiff. If the cap checks out good, then a hard start kit is the next option.

Yes, I do have a heat pump. I do have a multimeter, if that's what I would need to check the capacitor. I'm comfortable enough with electricity, especially since I would thoroughly look up how to do anything first.

 

[roughneck]

Probably duct bellowing out when the blower comes on.

 

[supers05]

Take a recording of the sound and post it. (YouTube link)

Cheers!

 

[subbuilder]

When is the last time you had your blower fan cleaned? It's not that hard to do. It'll take about two hours total to take apart, clean really good and then put back, if YOU"RE really careful. (Shop vacuum required).
Sub

 

[yuri]

Do you have a gas furnace or air handler?

Post the brand name and model #

If you have a furnace or air handler with a Variable speed drive ECM DC motor it will rock and thump when it starts. It is self adjusting. However it should only last a few seconds unless something is wrong with it.