View Full Version : old HP29 vs. new HP29

11-02-2008, 12:05 AM
Hi folks. Last Thursday I replaced a Lennox HP29-060-7y condensing unit thats about 10 years old with a new HP29-060-7y. New is lots bigger, but it could just have a single pass coil, not sure yet. Old one is double thick. Started the unit in heat mode with the 11-12 lbs of ***** that came in the unit. 260 psi discharge, 53 psi suction, 54 ambient, 104 supply. Good!, I thought. Switched to cooling-:(. 40 psi suction, 115 psi liquid line. Covered most of the condenser coil with cardboard and sat my scale on top of the unit to get the LL pressure to 205 psi. Had about 1 deg subcooling. Suction came up to 56 psi, superheat 15 deg.
Looks to me like low charge in cooling and possibly a slight overcharge in heat. I had about 30 deg subcooling in heat mode, but that is not a parameter that I am used to checking. Assumptions: Indoor and outdoor units are not mismatched (Lennox says they aren't), and the 11 point something lbs should be close to right (usually is).
I'm to go back to this beast tomorrow. I plan to start by checking od coil. If it it's double pass I'll know Lennox is wrong and they are mismatched. Next I'll measure airflow. After that I'll....?
Any thoughts on this will be greatly appreciated. Also, any opinions on indoor coil subcooling would be good.