Hello all, New member here looking to get some input on an home AC issue. Just a quick bit on me. I work on medical imaging equipment, ie, generators, small refridgeration systems, low voltage, and misc stuff like that, so I'm a complete newb. Now here's the issue. I came home a couple days ago and found the outdoor unit was not running. It's a 3yr old (was at home when we bought it) goodman GSZ130301 heat pump (heat and cooling), and a goodman indoor air handler. The thermostat was on and showing cooling, and the air handler was pushing air. I had a similar issue at the beginning of the summer with my downstair unit. So, I check breakers and obvious stuff like thermostat off/on. I pulled the panel off the outside unit and tapped the contactor and it started running. Thinking this was the issue I went back inside to adjust the thermostat because it was hot in the house and the thermstat went crazy. It was a honeywell touchscreen, and all the segments on the display would light up, then dim continuously. At that point I thought it was the thermostat so I bought another. I wired in the new thermstat and same as before, no outside unit. Here's where I start getting stumped. At this point I assumed my 24v transformer or contactor. So I went outside and measured pole to pole on the low voltage side of my contactor, no volts present with a call for cooling. I go inside and measure the output of the 24v contactor and have 27v solid. I happened to have extra parts from my last AC adventure, so I swapped the contactor and 24v transformer. No change. I should mention that I can push the plunger on the contactor and the compressor and fan will run, as long as I'm pressing it. I then start troubleshooting the circuit board and attached parts in the outdoor unit. Both the low and high pressure switches are OK. After more troubleshooting I thought it could be the board. I order another, put it in and same results. There's numerous measurements and troubleshooting involved in the above, but I'll give the jist of it below. I started trying to figure out where my call for cooling or heat signal was dropping off, and found this strange. Heres how the board is wired R - R from thermo Y - Y from thermo through high pressure switch C - from C at therm goes direct to contactor and splits to board. CNT - from board to other pole of contactor. CNT and C are supposed to pull the plunger in If I put my meter on both contactor poles, I get no voltage (0.3 or so). Now if I disconnect the Y from the board and measure the cable direct, I get my 27v, so I know I have a call for cooling. If I take the Y cable and plug it directly into the contactor in place of CNT, I still get no pull on the plunger. If I disconnect CNT from the contactor and measure it to C, I show about 9v. This makes me think it was a board/switch. But why would the contactor not pull when I directly apply 24v to it? Y - C I've tried 3 contactors, and swapped 2 into my other unit and they work fine. I've tried 2 transformers and 2 circuit boards. I have jumpered the high and low pressure switch (just as a test). Also borrowed the thermostat from other unit, no luck. I tried to ohm out my 24v wiring thinking i may have a short, but from what I can tell everything is good. I tried taking the incoming Y and C signal direct from thermostat and connecting to both poles on the contactor (bypassing the board altogether) and still get nothing. The contactor make 0 attempt to pull in. I am very stumped at this point. I have verified that the contactor, transformer, and thermostat all work on my other AC unit (rheem). I also troubleshot inside at the air handler, making sure one of my condensate switches wasn't causing issues, completely removing them. I removed the thermostat and physcially jumped R-Y-G, air handler comes on as expected, still no outside unit. I have all but given up at this point, but since it's Saturday I have to wait until monday to anyone. I figured I would post my tale of woe here and see if anyone has any new ideas. Sorry this was so long winded.

I have a few questions about troubleshooting small commercial refrigeration - i.e. undercounter refrigerators, pizza/sandwich prep cases, etc. I have a good understanding of refrigeration, superheating, subcooling etc. and am pretty handy with tools. I have several pieces of this equipment throughout our operation and would like to be able to do the first level of troubleshooting and possibly repair. My first question is if I have a piece of equipment that is missing the tag, how do I now what the correct charge, pressures, temperatures should be? Similar question with respect to freezers, I have several that have been worked by multiple technicians, etc. How do I know what the correct defrost cycle settings should be if I don't have access to the model number of the unit or the information tag? Finally, can I take the EPA 608 exam for type I certification unproctored (i.e. online) and be able to purchase refrigerant? Will it be legal for me to work on my own equipment then? Thanks