OK. It's my turn with an A/C problem.

I have a window unit, about 3 years old.  Fired it up last week, and it really blows ice cubes.  Yesterday, I turned it on and the fan blew air very nicely.  When I turned down the thermostat to engage the compressor, the lights dimmed and the fan slowed.  The compressor wouldn't run.  I shut the whole unit down, restarted it and it ran OK.

Tried to start it again this morning and got the same dim lights/no compressor problem.  When it does run, it runs great.

Any suggestions?

Possibilities include:  
Low line voltage, undersized wire or ext cord, bad start capacitor (run cap is OK), bad start relay.

More likely is that you are trying to restart it right after it has been running.  Takes 5 min or so for the pressure to equalize and allow restart with low torque unit.

Freebie:

All AC units and window units in particular need periodic BATH.  Out side coil needs washed, with garden hose, at LEAST once per year!

Thanks for the cleaning tip.  This was actually only used about 3x in one year, then stored in an inside closed.  You could eat off of it!

I'm used to the "let it rest before restarting" drill.  This has happened from a cold start.

How do I check the start capacitor and/or relay?

BTT for the night crew.

Can a brother get a hand here? [:D]

To test caps and relay:

Unplug UNIT!  REPEAT, Unplug it!

Remove front cover which usually gives access to electrical components.  Look for electrical diagram.  Scan it in here if you can - it helps to know which lavor unit you have.

Run capacitors are metal cased.  Start caps are always plastic cased.  Compressor will have three wires, often but not always black, red, yellow.  Run cap will be between red (run) and yellow (start).  A MALLER run cap may be present for the fan motor; ignore it as the fan runs okay.  Run caps are likely OK unless bulged.  Start cap, if even present, will be plastic cased and connected from run to a relay.  Relay will either be connected to start and common (black)[potential type] or line and run [current type] depending on type relay.  In SOME units the capacitor is mounted right on the large electrical box on the compressor, just as some fan run caps are mounted right on the fan motor.  Some units have no run capacitor at all (CSIR), others have run but no start cap (PSC).  The no start cap kind often benefit from a "hard start kit" which improves start torque.  (Makes them a CSCR system).

Before sticking your fingers in there, use a long screwdriver or jumper wire and discharge any / all caps by shorting them, terminal to terminal, NOT terminal to case.  After discharge (those things really BITE!) mark the leads and remove the cap.  Take it to a motor shop, HVAC or supply house and ask that they test it.  Purchase new for any bad ones.  SAME value is best.  Relay testing is difficult unless you have the right instrument.  Simple tests:  Current relay, turn upside down and use ohm meter across the contacts.  Should be closed.  Right side up, should be open.  Replace if in doubt, although they cause little trouble.  Potential relay contacts should be closed at rest.  Coil test with ohm meter will be several thousand ohms.  If contacts are stuck closed, start cap will be blown, often exploded.  

If you have an  amprobe, let me know and I will give you THAT method to check out!

Confused yet?  That's OK as more than a few techs have trouble with this part of the job!

Should I unplug it before or after I go fishing around the electrical connections with a screwdriver? [%|]

Thanks for the start.  I'll dive into it this weekend and, if I get lost, will scan and post the schematic if one is available.

Thanks for the help.