How is this thing SUPPOSED to work?

I have a 7 year old Goodman 3 1/2 ton "split system" heat pump; the compressor is about 40 feet from the air handler. The heat occasionally blows hot (120 degree) air for a few minutes, but then blows lukewarm (78 degree) air for hours, occasionally switching off for about 5 minutes.
Last February I had a similar problem, and sought help here. Then, the room temperature seldom reached the thermostat setting. A few brilliant people made extraordinarily insightful criticisms of Goodman, from which I could not afford to benefit by replacing the unit. Finally, last February, I called a factory-certified HVAC repair company which replaced the heating elements with higher wattage ones, and things improved. The serviceman returned last week, checked it out, and pronounced it "functioning properly."
But I still don't get it: why does the damned thing run all day long, even after it reaches the set temperature on the thermostat? Why doesn't it come on, blow hot air until it reaches the thermostat setting, then turn off until the temperature drops below the setting again?
I've got a graph that shows the pattern over an hour and a half:
http://img148.imageshack.us/my.php?image=hvac11009jm3.jpg
You can see that it only blows "hot" air for a couple of minutes - in this sample from this morning, it never made it over 100 degrees, although from time to time I find 125 degree air coming out.
I'm longing for the days of the old radiator systems. . .
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On Sat, 10 Jan 2009 13:55:05 -0800 (PST), DrYattz

You just havent been taught how a heat pump works. It extracts heat from the outdoor air (when its cold outside). The colder outside it gets, the less available heat there is for the heat pump to absorb (but it does still extract heat.) It aint gas heat and it aint oil heat but it DOES heat. The best way to figure it out is look at the performance charts. I higher outdoor temps you have lots of btu's available to heat with. When it gets to the 30's, 20's and lower, there is less heat to absorb so it runs longer and longer. However, if you were to look at the amp draw of the compressor you will see that also drops as the outdoor temp drops. Thus, it uses less electricity but runs longer. Eventually, it wont keep up and the supplemental heat will kick in, the register temp rises and the house gets warm quicker. The draw back is that your electric meter spins like a son of a bitch during that extra warming process. Just make sure the unit is properly charged, air flow is set correctly and the unit is clean (all of which requires a pro). If that dont work, move to a warm climate. Bubba
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wrote:

Bubba's my Hero... lol
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x-no-archive:

to the op
read about the "balance point" of heat pumps http://www.arthurhewett.com/id26.htm Mark
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On Mon, 12 Jan 2009 07:46:46 -0800 (PST), snipped-for-privacy@yahoo.com wrote:

There's not much to read about it. In a nutshell the balance point is where the heat loss of the building is the same as the heat output of the heat pump.
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Thanks, everyone. In fact, I was ignorant of the process of heat pumps.
Now I get it.
I don't like it, but I get it.
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Perry had written this in response to http://www.thestuccocompany.com/hvac/How-is-this-thing-SUPPOSED-to-work-36445-.htm :
------------------------------------- DrYattz wrote:

When the Temp. brops below 35 set the Thermostat on Emergency Heat till it warms up outside to above 35.
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