The heat exchanger outside never comes on. There is air moving through the vents in the house but it doesn't get cool. I expect I've got a start-up or run capacitor that has failed. How do I verify this and then repair it (I'm experienced electrically and mechanically).
Failed star/run capacitors are often bulged, sometimes even ruptured and/or have blackened spots around the leads. May be able to see that by just looking at the outside unit, sometimes even through the blades of the fan, but often need to take blades and the fan guard off.
Assuming you've checked the breaker/ contactor of the unit to eliminate something simple like a tripped breaker.
Anyway, getting back to the capacitor, if there's something wrong with it, replacement is the only option. Take the reading from the old one, check in hardware stores or online for the exact match or slightly higher capacitance/voltage. Never lower voltage but lower capacitance may work sometimes if you cannot find the exact replacement.
Failed cap is only one of the range of possible issues. Does the outside unit make any noises at all, any part of it turns (fan, compressor) or generates heat? Last but not least: what is the manufacturer and the model of the unit?
I purchased a replacement cap. today (the old one was bulged). I installed it and stood by the heat exchanger while my wife turned the system on. I could hear the relay clicking but the fan never came on. When she shuts the system off the relay will click, turn it back on it clicks again (it's trying) but no fan. The system is a Trane EX1200, 12 years old.
The clicking sound is the compressor contactor called for cooling. This means that the thermostat is doing its job and there's low voltage coming to the contactor (relay). There may still be no voltage on it if the respective breaker has tripped, did you check that breaker? I'm guessing it's probably safe to assume the compressor does not come on either - I think you would not have missed it if it did - it's the noisiest part in the unit when it's on.
If there's 230V voltage coming into the contactor (both live wires are, well, live) but the entire unit is still dead, it may be a bit outside of the DIY realm because there may be coolant leak or a compressor fault which is not really possible to fix without specialized tools and you would have to be licensed to handle the coolant anyway.
Look around the unit as well as the indoor coil for any signs of leaks, coil damage etc. , anything that can help identify the cause. Even if the repair itself is not DIY, you can help the licensed technician to get the picture quicker by giving him your observations and that might make his visit shorter and less expensive.
The breaker is OK (I turn it off every time I open the unit). I've checked the voltage and I've got 220 at the relay. No sign of any freon leak. The unit did seem to function for at least one day. I'm also thinking I've done everything I can and its probably time to jump into the shark pool and search for a professional.
<blockquote>I'm also thinking I've done everything I can and its probably time to jump into the shark pool and search for a professional.</blockquote>
This sounds like a very good idea to me. Please post an update here if you have a minute about the way the situation ultimately resolves.
The tech came out, got an insulated (fiberglass?) rod about the diameter of a pencil and poked the relay. It was apparently stuck from all of its attempts to start when the cap. was bad. It snapped into place and the unit started right up. I guess $200 for someone to poke it with a stick was appropriate since I never would have thought of it.
Sometimes you just have to know where to poke ... I don't know if this came out right...
Anyway, I just wanted to say that this was clever! My first reaction would be to replace the relay. Not all of them are serviceable, though. Come to think of it, solid state relay in this situation would do great. I have to keep an eye out for OEM solid state replacements, sounds like it could save some aggravation.
Thank you very much for sharing!