Or use a fan at night.
That, too. You’re much better off with this any time the overnight temp is under 70.
Sorry - didn’t note your location.
Do you have a separate dehumidifier on your system? Is it clean and functioning?
Since the AC is serving as a dehumidifier, there is likely much condensation of the evap coils (usually on top of the furnace).
That moisture will trap crud, whchi will insulate the coil.
I don’t know how your systems deal with that effect, but it may be worth looking into.
Meantime: yes, a 20 degree differential is about all you can reasonably expect. Since running the compressor cost both electricity and depreciation of the condenser, I suggest you listen to it and turn the thermostat up to turn it off when it gets as far as it can go.
I usually have mine set at 77, but when the temps go over 100, the compressor wants to run forever. I kick it up to 78 and give it a break.
Arkansas
Piecemeal construction by different people starting in mid 90’s we were told.
heat pump split unit
Lot of shade
metal roof
good insulation
dual pane windows, low quality
Will hold 66°F ( I like ) to 70°F ( wife likes ) 68°F is the compromise temp. Will cycle on & off, even during the mid-day full sun times.
Last house was 1960 Rock, metal roof 100 miles farther South in an area with 4-10°F average higher temps. Outside heat pump sized with full calculations + a slight bump up. Ducted into house.
Attic fan,
Added high quality gas filled dual pane windows.
Front & back doors leak like a sieve, need replacing.
Would hold any temp I set.
Cut $100 from monthly electric bill from original bill when we moved in.
Had a couple of occasions where upon return, due to power failure, inside temps were 90°F+, took about an hour to get back to 68°F air temp & cycling and 12 hours to get inside materials, walls, furniture, ceiling, etc., back to cool through & through condition so cycle was as slow as normal for this house…
Re cooling & reheating material other than just the air can cost significant $$$.
Our H/C man recommends, ‘set it & forget it’ as long as you you can / want.
Slow heating & cooling makes me want to shoot people more than normal, I avoid. For me, I have the bills to prove that for me, in these last two houses, a bit oversize makes significant energy cost savings.
Everyone else & all the experts can disagree. My billing history is what counts for me, not opinions from those not paying the bills.
Spring & fall = Wife loves fresh air, attic fan, report for duty.
Underground or cave house is my dream if the humidity is not excessive. Wife not impressed with that idea. I like wife so am still above ground.
I am impressed. How large are the house and heat pump?
Remind me to mock you in January when it’s freezing cold where you are!
1200? sq down south with the good windows, 4-5 ton maybe, been a while. Papers are down there. ( house layout sucks for air distribution. ) :mad:
Here is a 4 ton with 1580sq under A/C, 288 up stairs with vents shut. ( better shade here. )
Shade and high ground to the West is a major help. Less breeze though. :dubious:
79°F right now, working nice at 66°F inside with Zeus in and out 4-5 time per hour since it has gotten dark. 90+ during the day. Wife & I been sneaking the setting up and down 1 degree at a time between 68 & 66 hoping the other won’t notice. he he he 
I get my 66 at bed time cause she likes lots of covers. I don’t cover until Zeus leaves the bed. 
Ohhhhh I notice.:dubious:
Maybe 66 is fine for sitting in front of computers, but not so fun for regular living.
And I wouldn’t NEED so many covers or laprobe if it was warmer.
Ceiling fans help alot. Moving air is required.
I usually have intervals of going out to do yardwork to thaw out. Not this last month. This has been the crappiest rainiest hottest humid buggiest year in awhile.
I’ll second the ceiling fan suggestion. I had one sitting in the garage - only the master has an overhead light box and I didn’t know if it was mounted securely enough to hold a fan.
I decided it will damn well hold a fan or be replaced.
The room is easily 5 degrees cooler, and the feel is MUCH better - not as good as standing in front of an open refrigerator, but much better to have air flowing over your skin, Set for downflow and be sure to get a fan rated for one room larger than the one it goes in - they have multiple speeds out of the (cheapie) box, and there are now real fan controls plus light dimmer in a single box and wireless remotes.
Once more: do NOT try to use a light dimmer to control a motor. I don’t even want to guess what happens.
Yes Dear.
( My Mamma din raise no fools! )