Heat pump reversing valve failures can be easily confused with compressor failures. So we have to talk about both aspects of heat pump troubleshooting.
Once you finally figure out which component is causing the problem, then you have to replace them, which can be even worse. Many split systems are tall and difficult to lift a compressor out of. Reversing valves can be difficult to remove because they have four solder joints to deal with at the same time and, to make matters worse, they are very heat sensitive.