To Heat or Not to Heat, That is the Question!
In the last week, I have flown with two different pilots in airplanes with carburetors where they said: "I never use carburetor heat." Hmmm...right answer? I think the "never" is clearly wrong, but how about in routine conditions?
It all depends. If you are flying an older Cessna, beware. As the Cessna Pilot's Operating Handbook (POH) suggests, use it for descents and landings. This is because of where the carburetor is mounted on the engine and how the intake air is routed to it.
A Piper...different story. Because the airflow is typically preheated by its routing to the carburetor, it is less susceptible to carb icing. This doesn't mean it is NOT capable of getting carb icing. That is why Piper POHs say to use carb heat "as required."
AA5's, two different stories, I think. The mounting of the carburetor on the AA5A is similar to the Cessna with the carb below the engine. On an AA5B, it is on the aft end of the engine with air routing more similar to the Piper. The AA5 POH says to use carb head as needed. My point is that it is more needed in the AA5A than the AA5B.
At the very least, everyone should apply carb heat whenever the ambient temp/dew points are as shown. Note, it could be as warm as 102 deg F and if the dewpoint is right,...you'll likely get carb icing. Welcome to SC!
The disadvantage of using carb heat is that the air going into the carb is unfiltered. If the conditions were right for carb icing, using it for a limited amount of time might be the prudent answer at the risk of some particles entering the engine. The other disadvantage...it uses power. If you have to "go around," get the carb heat off as you add throttle.
Finally, if you actually have carb ice and then turn the carb heat on, the odds are the engine will run rougher until the ice clears as you are now putting water into the engine. Expect that. Do not abandon the attempt because of the roughness. That is what you want...the ice clearing the venturi.