Heat Pump will not turn on, contactor will not work

[dalebr99]

I have a coleman/Evcon/Air Pro Model DRHS0241BB heat pump, aprox 10 years old. Cooling well till yesterday and outside unit would not come on, fan and compressor, no joy. I took the control pan cover off and the contactor was kicking in and out and would make a big spark whe it did so. You could tell points were burnt. I looked at some of your earlier post and decided to replace contactor. Checked all terminals ends for snug fit and cleaned. Turned it on the first time and clicked once and then second time points connected and unit ran fine. 90 degrees ambient temp outside, 78 inside house. Unit ran for four or five hours and cooled down to thermostat setting of 73. Unit cut off and tried to restart in a few minutes and the same problem all over again. Big sparks and points will not connect. The wire on the left side of coil, yellow, has 26.7 volts unpluged, Right side small wire, Brown no voltage. Across the two will have 26 volts. I can push the points button and unit will start and cool well, although no voltage on either side of coil when points locked in. Just took a small piece of wood and wedged points in to get some cooling from the 90 degree weather. Checked voltage at Thermostat, R and B wire and had 26 volts. Changed thermostat to old unit that came with system that I replaced with electronic programable models whe new, no joy, same thing. Went up in atic and checked voltage on transformer red wire, 26.7 volts. Where direction do I go from here. Worked on AC on motorcoaches for 20 years (certified), but not so familar with house air electrical systems. This mobile home AC units are in a modular two story house of 1200 square foot footprint on each level, 2 ton, BTU Cooling 23000 BTU. Put two units in so air would get even regulated up and downstairs,installed by professional company. Please give speedy reply if you can. I am disabled and have son starting college this year. Really can afford to call tech out and pay big bucks for something I can do myself. I am afraid there is a break in the 24 volt wiring somewhere. Compasitor looks good, not inperfections. Please help!!

[dalebr99]

Really need some help guys. Unit started working this morning, turned off and on with the thermostat all day long until this evening. Now all the sudden the same problem, contactor sparks and wont stay in. I can hold the contactor in and it will run and cool great. Could it be high pressure cut off or maybe 5 minute delay relay going bad. I think the delay is made on the board, but not sure. The wiring diagrams for the heat pump are faded out and I can't read them. Can't seem to find any on the net either.

Please need help. Hot and stumped......Thanks!

[flcruising]

Have you checked the low voltage wiring at the unit inside the house for bad connections? I can't find any information with the model # given.

[dalebr99]

Have you checked the low voltage wiring at the unit inside the house for bad connections? I can't find any information with the model # given.

Yes I have run all low voltage wiring. I know this is going to sound crazy, but unit works fine during the day with hot temps, low pressure 55 -65, High pressure 175-190. At night the low pressure drops because of ambient temp and unit begins to fail again dropping voltage on 24 volt yellow wire. All I can figure is that the low pressure switch is bad, or the expansion valve bulb site needs cleaning or expansion valve needs adjusted or replaced. Got any ideas? Please help, stumped.

[flcruising]

Is the low pressure switch in series with the contactor? You know more about this stuff than I do, but I've never heard of low voltage dropping with low pressure or ambient. I also thought the low pressure switch was an on/off device, not resistive..? Any chance you could take that old contactor and hook it up at the air handler and see if it experiences the same issue?