Originally Posted by shughey00
Ok the motor reads 68 ohms so the winding isn't open.
SO which capacitor is the one to replace. The large silver cap with both the comp and fan connected to it is listed as the run capacitor on the schematic and the black solitary one off to the side is listed as start.
I mean seams the start is the one to replace but I think that is the hard start cap for the compressor..or am I wrong.
There is no start capacitor for the fan. The fan has only a run capacitor. The compressor may or may not have a start capacitor (depends on model).
When you examine the metal can capacitor you will see 3 groups of terminals, with the center group labeled "C" or "Common" one of the end groups of terminals will be marked "F" or "Fan", and the group on the other end marked "H", "Herm" or rarely "Comp". This device is actually two run capacitors in a single can, with both sharing the common terminal.
The fan uses the run capacitor that is between the "Fan" and "Common" and the compressor uses the run capacitor that is between the "Herm" and "Common".
Run capacitors remain energized the entire time the motor is running. They generate a good deal of heat, and thus are in metal cans to help dissipate this heat.
A start capacitor, if present, will be a plastic-cased device wired only to the compressor. It also will have some type of relay device to switch it out of the compressor circuit once the compressor is up to speed. If this start capacitor is not switched out, it will overheat and explode.
Your best step is to carefully remove the dual run capacitor - taking special care to tag each removed connection to identify from which terminal it was attached to. Then take the capacitor to an RV parts place, an HVAC parts place, or an electrical supply house. They will interpret the markings on the capacitor (microfarad and voltage rating) and provide a replacement.
A service tech, knowing what he is doing, can replace just the fan side of the dual cap with a replacement single cap. It'd only save you a couple of dollars over replacing the entire dual cap.
Most small (fractional horsepower) AC motors have run capacitors only. The role of the run capacitor is to increase the efficiency of the motor. It provides no "starting boost". It will, however, prevent the motor from starting if it fails open. Because a run capacitor is always energized, it undergoes a lot of stress due to heat and electrical spikes. They are the single most frequent cause of these motors not starting. Many perfectly fine single-phase, fractional-horsepower AC motors are changed when only the capacitor was at fault.
This advice provided free of charge by a 20yr licensed HVACR contractor and community college HVACR instructor.