We have had nothing but problems with the lennox mn hp29-311-1p condensing unit since we moved into the home that had the unit, it's about 7 years old. What brand can I cross over to?

Any brand will work. Make sure they are the same BTU( tonnage), or very close, same SEER and same Freon.

I agree with ma0641. Any "brand" of unit that is sized correctly and has the correct refrigerent will work with the existing line set and evap coil. However, the problems you are having with the condenser may stem from the evap coil metering device, maybe, maybe not. Most likely, if the unit is seven years old, it is an R22 unit. If you plan to replace the outside unit, you will be best off to replace the complete a/c system :condenser, lineset, evap coil. New units utilize R410a refrigerant and the oil is the system is not compatible with the oil used in the R22 systems. You can still get R22 condenser, but they do not come precharged, and the cost of R22 is quickly escalating. For best long term results, switch the complete system out for an R410 system, or merely hire a qualified tech to get your current system up and running the way it should be. Seven years really isn't that old for an a/c system, so you may want to give the current system one more shot at repair. Quilified tech is the key word here. Have them check everything: correct matching size of indoor and outdoor equiptment, correct charge, etc, etc. Good luck on your decision.

Take care.

Lee.