I have a lennox 2 speed condensing unit that is 25 yrs old and had very little problems with it. I cut the unit on last week and nothing. I took the panel off the outside unit to ck to see if I had voltage at the transformer and voltage coming from the house all good. I pushed the contactor in for the condensing fan and it worked. I did the same for the low speed and high speed contactor for the compressor and it also worked. The thermostat in the house allows the fan to come on and the high and low speed light on the thermostat to come on depending on temp. demand. I can hear the relays come on the unit outside. I have already replaced both potental relays last year due to the unit not shuting off. I had a repair man tell me that I needed to replace the unit last year. I figured this one out by myself. I also replace the time delay last year. What is the sequence of operation for this unit. To bypass the thermostat do I jump the same red and yellow wires? There is also two protection devices. I really would like to fix it can't afford a new one right now.

Sounds like a low voltage problem, with the tstat calling for a/c carefully check the tstat wire that connects to the contactor for 24 volts. If none start tracing the tstat wire looking for breaks or chewed wire an animal might have gotten to
But yes to bypass tstat u can disconnect red and yellow wires at the tstat and tie them together ,should make a/c come on