A month ago, I noticed that my 2000 Rodeo did not want to take off from a stopped position. I was pressing really hard on the accelerator and it just did not want to go.  So, I was on my way to the mechanic when the temperature needle starting going up.  It never went all the way over to the H, but about 3/4 of the way over.  Then about 1/4 mile from the shop, the speedometer needle and the rpm needle started swinging back and forth and then the engine light came on and the battery light came on.  At this point, it was like the car just did not have the energy to go.  I pulled into the shop parking lot and when the mechanic came out, it was dead and he had to jump it to get it in the garage.  As it turned out, it was the alternator.  So the alternator was replaced and while there, I had the a/c recharged.

A week later, someone at work came in and said I was losing antifreeze.  I opened the hood and there was this skinny hose that had a tiny pin hole in it and was spraying a fine mist of antifreeze.  So I take it to the garage around the corner from work and it was the bypass hose.  Had that replaced.

Now this week I noticed that when I am driving in traffic or sitting in the drive thru, my a/c seems to quit cooling.  The air being blown out is significantly warmer than when I am driving 45 or faster.  So today, while on the highway, the a/c seemed fine, when I got off to drop off a passenger, my a/c stopped cooling.  I was turning to get back on the interstate and noticed that the temperature needle was about 3/4 of the way over.  I went ahead and got on the highway and it immediately came back down, but I had turned off the a/c so I don't know if it started cooling again or not.

 Do you think the 2 recent repairs could be related or is this something totally different?  Do you think it is the thermostat sticking?  What could it be.

My guess is what you're experiencing is every rubber part in the car dying at once. Have you ever changed the radiator hoses? Heater hoses?

Another guess is a stuck closed thermostat.  

The a/c is, in my estimation, an unrelated issue...an 80 year old man has heart trouble and dementia. Not related but simultaneously.

Your car overheating could be a faulty thermostat, but don't just replace it.  To check it, let your car warm up and touch the upper radiator hose going to your thermostat.  BE CAREFUL.  It might be hot.  If it's still cool, then I would replace it.  It means it's not opening to allow flow.  If it feels like it's hot, then I would probably rule it out.  You might want to get your radiator looked at instead.  Maybe just a flush or replaced.  As for your AC.  At 45 mph, your engine is spinning a lot faster than when you're at idle.  Try holding your engine up around 2000 rpm to see if it's the speed making this change or your engine speed.  Only do this to check it, not all the time whenever you're stopped.  If you notice a difference and it's the speed of the engine, your compressor might not be pumping as hard as it used to or a few other things. An AC repair shop should be able to help you with this.

Friend, it is 100 % your Thermostat...

Some times it gets stuck and the fluid does not circulate...and cause over heating ...especially when you drive with A/C ON....

First try with a small hammer tapping on the Thermostat housing; it is where the radiator hose goes in on the engine block ...few gentle hits should release the stucked thermostat....

If it happens again, you should change the thermostat!!!

check your realy switch or the thermostat. I have same problem back then, turns out its just the relay. Don't know much about youre previous problems but i think it didn't cause the latter headache!

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I have a 1998 Isuzu Rodeo that began to overheat about a year ago. I flushed the system and the problem went away. It is possible your thermostat is sticking, but a good flush should resolve the gunk that is making it stick. It is the cheapest fix to try first. I also found that by using Redline WaterWetter in the new antifreeze, the truck runs cooler.