Heat pump runs/buzz/no heat

Dearest hive:

my heat pump(2.5 ton coleman, 2015 or so install) is not making heat. We haven't used AC since mid august so it's been dormant a couple months. Turned on heat, house not getting warm, furnace fan doesn't stop. A couple years ago I had to replace the control board in the outdoor unit. 
 

the fan on the heat pump is running, but it sounds like the compressor is not kicking on. Definitely just have fan noise at the outdoor unit and no low hum of the compressor and the lines are not changing temps. Every couple minutes for about 3 seconds I get a buzz in the outdoor unit. 
 

hvac was never my specialty. I gather an internal component has failed and I will need to replace it, but how do I figure out which one? 

Sounds like a capacitor for the compressor has puked and the compressor is cycling against the thermal overload switch. 

Could also be the contactor.

The compressor could also be locked up. 

Figuring out which one is going to require testing. I'd start with the contactor. Test for voltage on both sides of it. If it has voltage and the compressor isn't running I'd go to step two below. If it doesn't the problem is with either the control circuit or the contactor itself. 

Then I'd move to the capacitor. There will be numbers on the side of it. Look it up on Amazon. They are about $15. Replace it. 

Edit. Make sure you power the system down and ground out the capacitor before messing with it. They can hold a charge for a while and zap the crap out of you. 

Thanks for the flow chart. Thankfully the plumbing and electric supply house i have an account at is right up the street and a massive hvac supplier also so most stuff i can probably have in my hands in 10 minutes

Since the fan on the outside unit is running, that tends to point to the capacitor. The contactor supplies power to both the compressor and fan when it closes. Usually, a failed contactor will present as neither fan nor compressor running which isn't the case here.

I'd bet you need a capacitor. Make sure the replacement matches the microfarrad rating on the original. There's three terminals on them which are usually labeled with "h" "f" and "c", hermetic, fan, and common. Make sure to get the proper wires on the proper terminal. Just swapping them over one at a time is the safest bet.

I usually tell people to buy an extra capacitor and keep it on hand. More times than not, it will save the day and get a guy back up and running quickly and avoid a trip to the supply house or a weekend crisis. Spend the money on USA made capacitors. They will have a prominent flag printed on the box. They really are better and worth the added dollars. 

In reply to Cousin_Eddie (Forum Supporter) :

Yeah i was about to ask if a failed cap with 3 terminals could show as a fan works/compressor doesn't situation. The funny thing is whenever anyone asks me about heat pumps not working I tell them buy a capacitor first, then when it comes to my own E36 M3 I don't trust my brain. I've been on construction sites with hvac guys, done furnace installs, fixed other stuff, one would think my head would learn to trust itself occasionally. 
 

going to see what they have up the street soon, got a pic of the label to take with me

Replaced capacitor, no change. The few second buzz is definitely coming from down in the unit and not up in the wiring/control panel area. 
 

Currently hunting for my multimeter because why would it not be where I thought it was

I have found that insects/spiders have a way of finding their way into contactors during periods of light use (Spring/Autumn). 

Patrick said:

Replaced capacitor, no change. The few second buzz is definitely coming from down in the unit and not up in the wiring/control panel area. 
 

Currently hunting for my multimeter because why would it not be where I thought it was

If you're like me you have to ask your son if he has it like I did yesterday.

Found it. Have voltage at both sides of the contactor. I'm standing here testing and the buzz happened again, then a minute later the compressor just kicked on and started making heat. I have no idea what is happening but maybe it just fixed itself

Insects in your contact points is likely the culprit. 
 

You can pull (or switch) the disconnect to kill power to the outside unit and wiggle, jiggle, spray contact cleaner, etc to clean them out. 

For some reason I am now unable to upload pictures of the capacitor box. Forum update I guess.