October 19th, 2009


A Cold Wind Blows... Inside

Null Heat Pump

Back in April we had The 2009 Great Heating and Cooling Project. Above 32°F, heating is done by the Goodman 2-ton heat pump. Basically, it's an air conditioner run backwards, so hot exhaust gets dumped inside and the outside gets the cold air. Amazing that it actually works.

It's also a little bit odd, because the air coming out of the ductwork isn't hot-hot, like the warm arm when the furnace is running.

Last Wednesday I realized that the heat pump wasn't really warming the house. Outside temp was near freezing, about 34°F. Overnight we let the house cool down, but in the morning after running for an hour-and-a-half it had only gone from about 68°F to 69-70°F. Later in the morning I raised the set point again and after 45 minutes, again only 68°F to 69°F. So I shut down the heat pump and switched to the furnace full-time. Went from 69°F to 72°F in 10-15 minutes. Ah... warm.

Strange Noises

The other symptom: late one night, when the outside temp was 36°F and the heat pump had been running, I heard a 10-15 second long grinding noise -- like the compressor was restarting. Heard that sound during the long not-so-much-warming incidents on Wednesday, too. Hmm...

Overfilled At The Plant?

My heating and cooling guy, Greg, checked out the heat pump and found that it was running, both in heating mode and cooling mode. Worked real good as an air conditioner when the outside temp is 47°F. (grin) The pressure and amps were a bit high, as if it were working a little harder than normal, but it wasn't out of refrigerant (my initial guess). He wondered about the TX transfer valve, the valve on the inside of the heat exchanger that has to switch between heating and cooling. He left to go get a TX valve, but the supplier said that the manufacturer had reported that some heat pumps had shipped with too much refrigerant, up to two pounds, which would cause too high a pressure and in cold weather, i.e., the unit might've been freezing up.

The installation papers had pressure charts for AC mode in temps above 60°F, but not in heat mode. Greg was able to get those figures and found the pressure while running to be high. So he hooked up a tank and removed some of the refrigerant to bring the pressures down to the new tables he'd gotten for heat mode. Reweighed his tank and it was nearly two pounds heavier. Considering the total charge is supposed to be five pounds, it was definitely overcharged at the plant.


Running the heat pump, the air coming from the vents actually felt warm -- still not hot like with the furnace, but I wasn't expecting that. AC mode would've been working okay, given that the outside temps would've been hire, but the amps to the compressor have dropped so it will run more efficiently in the future. In the spring, when the weather is back up to 70°F, Greg will come back and check the pressures for cooling mode.

While it is annoying that someone screwed up at the plant, it helps that the heat pump and the furnace complement each other, so we have a back-up heat source. (grin) Of course, it's now about 60°F outside, so the heat isn't running. But hopefully we're back up to full power.

Dr. Phil