Coleman Mach 3 ac unit tries to start compressor & kicks off

I would check thermostat first. Remove compressor wire from thermostat and see if that cures starting by itself.

Check that incoming voltage is up to specs at AC unit control box ( 110-120VAC ), and if good, I'd suspect start capacitor for compressor is defective and needs replacing provided compressor is good. Usually a new capacitor is required in most cases. Please don't try changing it yourself if not experienced in that area, as capacitors can give a very high voltage shock, even with power off.. Don't forget to turn breaker off to power source before working on it.

Have you checked the high and low pressure switches on the unit? If you are cycling on and off, look at your pressure switches to see if they are opening during operation. Also, when was the last time you cleaned out the condensing unit coils with soap/degreaser and clean water?

Sounds like you have dirty condenser coil or bad condenser motor if it runs fine in the night

Here's a link to a service manual, with step by step tests to determine whats wrong. I'm thinking compressor shot, but this should confirm, and or help you determine for yourself. Be careful with those capacitors eh !! Read warning in service manual.

http://www.rvcomfort.com/pdf_documents/1976141_copy.pdf

Take a look at your start capacitor. This the capacitor that kicks the compressor over when it tries to start. If the capacitor is bad, it cannot kick the compressor back over after the first cycle because the head pressure has not evened out yet. It is located in the upper unit on the side panel in a small box. Be careful, highly charged capacitors can zap you if you are not careful. Disconnect power and touch across the terminals with a meter or a screwdriver to discharge the capacitor.

Hope this helps,

Jeff

If this is a ducted unit, check the thermostat. It has a fuse for protection that may have blown. If the fuse is fine and you have power to the upper units control box, check for 120V incoming power at the control box and also check for incoming 12V on the Yellow and GH wires when tstat is set to high cool.

Hope this helps.

sounds like the unit is low on freon. it will need to be serviced so the leak can be fixed then recharged.

I had a problem with my coleman mach 3 AC, we were at an RV park up at lake shasta CA and the fan would stay on but the compressor would come on for a few seconds and then trip off. It was the motor overload relay on the compressor that was tripping. the RV park was old and apparently the wiring to the panelboard at the RV park was too small, when you are drawing a lot of current there was too much voltage drop across their line, to make up for this the motor tries to draw more current and heats up the motor overload and it trips off. I solved this problem by buying an autoformer from Camping World, it senses a voltage drop and automatically boosts the voltage.

I am now having a seperate problem, the compressor is either locked up or has too much back pressure and trips off the service breaker when trying to start. The only solution I can see with my current problem is to replace the entire unit.

I changed out the startup and run capacitors. A/C runs fine now