Hey guys.
So I live in a small 600 square ft apartment inside an 1880s, very energy inefficient, house.

I was having all kinds of problems with the heat pump/heating unit outside.

A tech came today and said the freon was low which was causing the emergency heat to run.

Thought that would fix it, but I'm still having issues.

Mainly, if I set my thermostat to say 67, and the temp on thermometer was 64. In about an hour it will get up to 67. When it reaches 67, the system just keeps running. The air once it reaches 67 seems to feel cooler coming out of the vents. Sometimes it stays on for hours. The temperature here outside right now is around 35.

The system will shut off if I set the temp one degree lower, so it seems to be working there.

Does this make sense? Is it normal and I'm just being paranoid?

I've read that heat pumps run longer, with "cooler" air, but I'm just not familiar enough to know if I should keep pushing my landlord to fix this.

Thanks!

Possibly a thermostat issue? Are you sure to room air temp is reaching 67? What happens if you go above 67, say 69. Does it shut off when reaching temp?

According to thermostat, it reaches 67. Another thermometer I have is about 3 degrees lower, but they are consistently 3 degrees apart so I think it's just the differences in the thermometers.

No matter what I set it at, once it gets to that temperature, the system just stays on. Turned it up from 67 to 69 about 1.5 hours ago, and the system has not turned off since. But it has been at 69 for at least an hour of that

If it gets to 69, and I turn it back down to 67, the system shuts off, and will stay at 69 for quite a while, which is why I'm confused that the system doesn't shut off when it hits the temperate I set it at.

So regardless of it set temp, once it reaches it it stays running and if you drop it one degree, it shuts off?
When it is running to get up to temp, the out put air temp is X. When it reaches temp and then continues
to run, the output air decrease in temp? and it is just the fan that remains running?
What's the age of the system?

Yes, that's correct. Once it reaches set temp, it keeps running. If I drop the set temp 1 degree, system shuts off.
It seems like once it reaches set temp, the air blowing out of the ducts feels slightly cooler. Maybe my mind playing tricks on me, but feels to be a definite difference.
Before they fixed the freon issue, the system shut off but fan kept running. Now both the system and fan keep running.

I believe the system is basically new. Within the last year or two.

Ok, back to the thermostat. Is it the type that has the auto on and constant on feature?
Could be shorted internally or wired incorrectly. Has it always done this or just started?
By the way, I am not an HVAC guy, more of the all around handy guy out of necessity over the years.
So I am just running through the possible suspects/process of elimination. There are only so many
things in the system that can fail.

Does the fan on the outside unit shut down? edit: answered above that both the blower and system continue to run...

Does the blower/output air speed/volume change at all when it reaches temp but continues to run?

It does have auto on and constant on. It is set to auto on. I have only noticed it recently

Not that I can notice. The fan blows pretty hard all the time

How old is the unit? What size is the unit? And what temp is it outside.

Not old. Less than 2 years. Not sure of size, not home right now. Temp out has been between 25 and 35

Not an answer to OP's question....

.....but I will add that, in my experience, heat pumps are a terrible choice for anywhere
that seasonal temperatures are not consistently 40 degrees or above.

Since you have aux heat, this is not a mini split.
Central air Heat pumps, for the lack of better words, suck.
A lot will come into play such as ambient temp, heat loss from ductwork (poor insulation length of ductwork runs, where the return air is located, supply air locations, fan speeds, etc.
the most efficient heat pumps are the mini splits (wall units) due to no duct work. No heat loss. The efficiency ratings are through the roof on some units.

Typically with your setup, poorly insulated house high heat loss, 20-30* ambient should barely keep up. Depending on the efficiency and the size of the unit of course.
There is a possibility the unit isn’t sized right. There are a lot of factors.

You could also have a 3 way valve issue as well. The unit could be icing up outside and not defrosting, which will make the unit run as you describe. Maybe it’s stuck, etc.
Remember, your body temp is 98*. The temp of the supply air may feel cold, but it can still be in the mid 90’s. Which will still heat the house.
Check your air filter.

Let it rip again, go outside after 20 minutes, feel the bigger line at the condenser, it should be nice and hot. Look at the condenser coil outside. Check for ice, heavy frost, etc. if it is present, and the unit isn’t defrosting you could have defrost control issues or 3 way valve issues. Call the tech back.
Shine a flashlight through the condenser at night, if the light goes right through it no problem, it’s clean. It could be dirty though, which will hurt the performance as well. It can be cleaned in 15 minutes with a hose gently.
Try turning the unit to ac, let it run for a couple minutes and switch it back to heat. Maybe the 3 way valve is sticking .

Awesome. Thanks so much for the info and suggestions! I will try these.
Starting to think I might be overthinking it and it's just a very very poorly insulated house and I have to suck up the super high bills (they're double what my last apartment was, which was twice the size...but basically new and on a middle floor)

I will keep troubleshooting!

Since you rent....why is this your issue to fix? It's your landlord's responsibility to fix it.

I can't speak for all states but normally the landlord is required to provide a working heating system, along with a working water system, electrical system, and sewage system.  If the heating system doesn't work, in some states you will not be required to pay rent (in a subsequent civil suit) for the period of time that the heating system didn't work. That said, it sounds like your system is working....but the lack of insulation is the bigger issue as far as heating bills are concerned.

That's not true for the newer heat pumps. The current heat pumps are light years ahead of the old ones.

Just had a new dual fuel Heat Pump installed in October.  Thing works amazing.  Temp above 40 and it runs the electric heat strips, temp drops to 40 and the heat strips kick off and the gas kicks in and it'll keep my house as toasty as I want.

Many heat pump systems do not work all that well bwelow 32 F.

The outside coil falls below 32 F and frost forms n them further killing their efficiency.
Some units wil repeatedly enter short defrost modes to try and eliminate the frost that has formed.

They actually turn to cooling mode and turn on the backup heat source to not cool the conditioned space.

Is your thermostat designed for a heat pump?

I have had two heat pumps in my lifetime, the first one and the last one. I absolutely hate the fu%^$#@