I live in the desert of CA and I am currently using a swamp cooler. I am considering installation of a new HVAC system. When the house was built I had the builder install dual ducting (one set of ducts for the swamp and one for the heater and future A/C). I also had proper wiring installed from the main breaker box to a disconnect box near where the future condenser will be. also included were the liquid and gas coolent lines, 3/8” OD and 7/8” OD respectively. The distance from the future condenser to the future evaporator is approximately 40’. The coolent lines run through the attic and down through and exterior wall, they are attached to the frameing and covered with stucco. The specs on the new A/C system, I am considering, say 7/8” OD gas line can be used up to 25’. Any thing more than 25’ requires 1 1/8” OD gas line. My question is: Can approximately 15’ of the 7/8” OD line be left in the exterior wall and connected to 1 1/8” OD going the rest of the way to the evaporator and not affect the operation of the system? This would save having to run the new gas line down the outside of the stucco and fabricating a cover for it.