my wifes 2007 malibu, heater blows cold air. but when i rev the engine, it gets hot. but then cools down when i let off. ideas?

I have an 07 Malibu Maxx LTZ . I have noticed the same issues, however, the air gets warm-hot ONCE I START DRIVING. I'm awAre that when you put on the front defroster, the compressor/AC light comes on (this is the climate control on my model) of course it s gets warmer as you increase the temp. Not sure if it's effective to use the "auto" setting on both knobs. It also, when its not on both Auto settings (fan speed & function knobs-left and right side of console) Either the light for outside air or the light for recirculate is on... You can switch your preference). Why does the AC light come on when its on the defrost/defogger only setting or combo of that and upper air flow? I believe that tells you the AC compressor is on.. But why? It does seem odd that air ONLY gets hot when car is in motion. I guess I am providing a feedback, answer and another question all in one. I had an 04 Maxx which got totaled. I miss the document clip it had on the driver side of the inside windshield. Great for handicap placard, toll ticket, etc. I could not find an easy way to remove it and put it in the 07 , but no biggie. I have about 82,000 miles. Love the rear DVD. Sound is awesome.. Watching concert DVDs ..when I'm not driving of course. I have the 6cd changer. A former service writer at the dealer said not recommended using CDs made at home... Makes no sense. If its mp3 it works. The tweeters up top really help. Great sound. Sometimes I wonder if there is a hidden subwoofer. The fuel economy sucks. Rarely do I get 20mpg. Maybe in Highway driving. I get 17.5 to 18.5 city. My car is almost paid off. I hope to get 5 more years out of it free and clear. Nice rich color.. Silver stone. But next time I buy another car, NO MORE 6 Cylinders. I see no reason why the Maxx was not available as a 4cyl. I would hAve opted for that! The rear seats, plenty of leg room, slides back and forth and reclines a little. I see why the Maxx was discontinued after my 07. The new style in 08 did not lend itself to a Maxx like style. Before I got laid off, I was set on an 05 Equinox....several k's cheaper, I like my Maxx overall! Any other info regarding the climate control? Also you can email me: Designer58 at Comcast dot net.