I live in north central Texas. My AC runs May thru Sept. This last year I noticed condensation around the vents in my Living Ceiling causing water spots in the ceiling. What is causing the condensation? How can I stop it?

North Alabama Temp outside last week 5F Now 24F@3AM House 2445 ft square heated & cooled Marvair 48HP 42.5 amps split system with 7.5 kw strips in attic. Honeywell heat pump system thermostat. Unit was new in 1978 but we have replace compressors every 6 years since new. Just outside 5 yr guarantee periods again. In 1996 replaced compressor, reversing valve, dryer, motor contacts, both inside and outside fans, and thermostat. Tried to have relays replaced but could not get new circuit board with the three relays as Marvair is out of business. Problem is not enough heat at the duct. Duct temp with heat pump only 73F with strips on 80F. Baseline conditions when all is perfect is 115.6-119.2 with strips on. Baseline without strips 101F. Circuit breakers 220v both are okay, fuses in control box at strips all test okay. Large freon pipe is hot to touch at outside unit. Freon psig was 118 & 155. When on, heat pump only, unit runs 100% of time and never reaches normal temperatures. With strips on same thing. We are only asking for 72F on thermostat. The coils outside had some frost, but no ice, like I saw years ago, prior to a fix. It appears to go to defrost mode way too often even though it shouldn't. Almost everytime it comes on it blows cold air down to 60F=maybe the cold air coming from ducts in cold attic and not defrost cycle. We have turned back the thermostat to stay off 100% of time and bought (2) quartz 1500 space heaters. We have closed off 1/2 the house, and are living in the kitchen, family room, and two bedrooms and two baths. It is staying at 66-68F in the used living area. this AM. The closed off house is 54F. These Marvin Quartz heaters are really nice! I am think of installing another one on the ceiling in bedroom and running a 12 gauge 20 amp circuit breaker for it use only. As an Engineer I am very unhappy with the reliability of these heat pumps and they require much money in annual maintenance. In 1996 we spent $1300 repairs hoping we would have reliabilty. Now, we are living like we did in the 50's. Do I have a major problem, again, like compressor, reversing valve etc? I looked at the coil, in attic, and it is like new externally. I have a spare motor, for attic, and outside unit, stored for use. The outside fan motor at times does not run even though I hear the compressor running. I was about ready to change that moor and the darn thing started running. I have a clamp on amp meters and volt ohm meters and freon gauges. I believe my relays are bad and they are Honeywell types mounted on a small square circuit board. I have not been able to remove them, for replacement, or to get their model numbers. Every change of seasons, I have to turn off the power, discharge the capacitors, and work the relays manually, as they appear to be stuck in the wrong season setting. I work them by hand, springs at top, and spray with electronic cleaner. Sometimes I can hit the aluminum cabinet, at the electrical panel corner, with a hammer, and the heat pump will then start cooling for the sumnmer or heating for the winter. This saves removing tow sheet metal covers. This year nothing is a fix!! I have been willing, to put up, with this, as it is a real challenge. As, I am now retired, I have devoted, my life, to make this thing survive for a few more years. Nevertheless, I am about ready, as soon as weather permits, to design a "SYSTEM" which will be rather simple and involve very little mechanical and eletcrical equipment. I have read about geothermal systems, but they still have the compressors. My new system, will involve a hot and cold cistern, with two pumps. One pump will pump water from the cold cistern to the roof with black solar type glass covered panels to absorb the suns heat. These will drain downward by gravity as they absorb the sun's energy into my hot cistern. The hot cistern and a discharge pump will circulate hot water to a coil in the duct=maybe use the freon condenser, already there. Then flow back to either the hot or cold cistern depending on its temperature. Water to keep the cisterns full, will be provided by rain(we get 47 inches /year here) and a gutter system. Pumps are very reliable and new types of centrifugal pumps do not have seals as the output is out the center. What does everybody think?? Can I repair my antique Marvair, once again, at a cheap relative cost or should I begin my design of my super efficient 50 seer sun-water-air system?? I have not yet checked on the number of hot sunny days in Decatur, nor have I sized the cisterns. A geothermal requires 1000 ft of pipe per ton and on a 1/4 acre I may not have the space for such a system. I really want a perfect system that I don't have to marry the repair man or pay his country club membership and Mercedes payments!!! Thanks for all replies..