Last summer, after having the AC motor replaced, the speedometer developed an odd malfunction. It worked fine until I had driven a few miles and then it would shut down completely and stay off until the engine was cool again. This was during the summer while the AC was on. Now that we're in the colder months with the air conditioner off, the pattern is the opposite. A cold engine or cooler ambient temperature means no speedometer, but on a warmer day, no problem and likewise when I've driven a while and the engine is hot, the speedometer comes back on and stays on.