My GE Weathertron heat pump failed after squirrels chewed through the vinyl jacket on the low-voltage wiring, causing the compressor to repeatedly cycle on-and-off, ultimately burning out the motor. Until then, the pump had worked reliably for 30 years.
I wanted to replace it with a unit of similar dimensions to ease the installation. I learned that the GE Weathertron product line had been sold to Trane, so I bought one of Tranes units and discovered that the company had "cost-reduced" the product. This move introduced a few weaknesses into the design.
One day I noticed that the fan on the Trane model was cycling on and off. After some poking around, I noticed that the cycling changed when I moved the wires. I found that the "FASTON" connector had failed. These connector assemblies include a tab mounted on a circuit board and a slide-on receptacle crimped to a flexible wire. The crimped-on portion had fractured, right where the crimp meets the receptacle.
Fortunately (I thought at the time) the terminal strip where the break had occurred was right at the outside panel surface so it was easy to remove the connector and crimp on a new one, even though the wire lead was short, and I had to uncrimp the old connector and crimp the new one onto the same point.
A few years later, the unit ceased to run during the coldest part of the winter. As I was moving my voltmeter down the terminal strip, checking voltages, I caused a spark and the unit started up again. I found that another connector had fractured in the same way as the first.
Then I realized the cause of the problem. The relays (HVAC tradesmen call them contactors) were mounted on a bulkhead parallel to about three inches (75mm) back from the outer surface panel where the terminal strip was mounted. The interconnections were made with fairly heavy stranded wire, maybe AWG 16, with very little slack in the wires. When the compressor ran, the inner bulkhead would "drum" with respect to the outer bulkhead.