Heat pump - supply air temp warm


Old 03-11-14, 07:16 PM
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Heat pump - very cool supply air temperature


Subject should say "very cool supply air temperature".

New to heat pumps, not an HVAC expert but understand enough of the basics.

Just moved in to a house with a heat pump and received my first electric bill - $600 - which surprised me because I haven't been living in the house and the heat pump has been set at 62 deg F for the month!

House is in central PA. Condenser and blower are both Philco units, 5 ton capacity (2-stage condenser I believe). I believe the air handler is variable speed. House and units are about 5 years old, 3200 sq ft. Thermostats are Honeywell 8000. The house has a two-zone system managed by an Arzel panel, which seems to do much of the control for the heat pump. Aux heat is 2x10KW heat strips. Fresh filter.

Ran the heat pump tonight with an outdoor temperature of 50-55 deg F. Put in a setpount of 66 deg F with an inside temp of 64. I thought for sure this would be the best time to start troubleshooting because our weather has been exceptionally cold the past month and I didn't want to troubleshoot when the system was at its most inefficient.

Vapor line to the air handler got HOT (to the touch). I measured 100-130 deg F using my infrared thermometer gun. Arzel panel was calling for Y1 and Y2 stages from the condenser. Ran it this way for about 35 minutes. Measured return register and supply register temperatures at 62 and 65 degrees respectively. 3 degree temperature split? No way that's going to heat the house. Confirmed that the LAT (Leaving Air Temp) on the air handler was at 65 deg, per the Arzel panel and it definitely felt cool to the hand.

Starts to help me understand why I had such a high electric bill for the past month. I've probably been recirculating interior air and heating it (barely) by circulation, not with the heat itself.

Switched the system over to emergency heat to engage the heat strips. Lights dimmed, sure think the electric heat came on. Ran it this way for 10 minutes. Measured register temperatures again - no change!

What gives? How could I have a hot coil or hot electric heater strips and not be getting warm air out of the ducts? This has me baffled. Being that it's independent of first and second stage compressor operation AND electric heat, perhaps an airflow problem? But where to start looking? Too much air?

Thanks in advance for any thoughts!
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Old 03-12-14, 09:46 AM
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Sounds like a return air duct leak or a large outside air duct with no damper.

I'd take a measurement at the return air grill and another temperature measurement a few inches from the air handler intake with a digital meat thermometer to look for a difference to help verify this.

An infrared thermometer should not be used to measure air temperature.
Old 03-12-14, 10:36 AM
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Lights dimming probably means the heat strips are bad. The large pipe should be at least 150F when outside temperature is 55F.
Old 03-12-14, 07:37 PM
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An update based upon an experiment I ran tonight.

Set a big temp differential to see if I could even warm the house up. House was at 60, set the t'stat to 68. T'stat showed "AUX HEAT ON" telling me the electric strips were energized. Zone panel showed Y1, Y2, and W1 outputs active, telling me it was calling for both stages of compressor and electric strips.

Surprisingly, the supply started warming up! I had a 97 degree leaving air temperature (measured by zone panel in the supply duct) after about 5-10 minutes and the house warmed to 64 degrees in about 15 minutes!

Turned it all off, waited about 5-10 minutes and figured I'd give a shot to a smaller temperature differential. Put a setpoint of 66 degrees with the house at 64. No "AUX HEAT" on the t'stat and zone panel was calling for Y1, then Y2. Similar feel of a hot vapor line, but the leaving air temperature began to rise, all the way up to 99 degrees! Can't confirm if the strips were definitely off (nothing seemed to be calling for them), but once again, the house warmed!

Completely baffled at this point. Only difference is that the outside air was at 29 degrees today, while it was 50-55 degrees when I was trying this the other day.
Old 03-13-14, 03:35 PM
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could be that Philco control activates some or all of AUX heaters when ambient is what they regard to be low enough that the heat pump can't do the job - do you have the Philco install manual ?
So at 55 no boost neede - just the heat pump, at 29, assist from AUX heaters.

Just because the vapor line is hot doesn't necessarily mean that heat is being transferred;- is the liquid line warm ? You might be low on refrigerant.

dimming lights could just be that your electric supplier has inadequate equipment - e.g. transformers, line size, etc so that the extra neighborhood demand is beyond what their equipment can handle.

$600 for a 3500 sqft house doesn't seem excessive for your location, and this winter's temperatures
even with indoor at 62F --- If ambient is 20F then the temperature differential for heat loss is 42F; if indoor is 70F , ambient 20F, then the temperature differential for heat loss is 50F - roughly 16% more ... a lot or not depending on your world view
Old 03-14-14, 04:40 AM
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Figured out the relationship between the thermostat and the Arzel zone panel last night. The zone panel does most of the control of the system and I finally understood how to ready what it's receiving as "inputs" and what it's sending as "outputs".

The issue is with the refrigeration loop of the heat pump. The heat strips are working fine, and as a matter of fact, when they are energized is the only time I get heat. They were locked out due to a high outdoor air temp last night.

The low temperature split between supply and return (i.e., no heat) occurs when the first and second stages of the heat pump are running alone, no matter what the outdoor air temperature.

So it looks like it's trying to understand why the hot vapor line is not transferring heat to the supply air. At my threshold of knowledge, so I'm going to have to call in a professional to take a look at the refrigerant.

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