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Temperature Readouts for Heat Pump

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PopcornSutton

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Jun 10, 2024
Messages
784
Location
Northern Tip of VA
I installed the heat pump in our house about 10 years ago. I have checked the charge using super heat readings a few times and it has held fine. I have had an old analog/capillary tube temp gauge (salvaged from a demo job) in the supply duct for a long time, and I would glance at it and knowing what the return air temp should be, give me an idea if all was well.
I ran across some digital temp gauges on Amazon, 12 voltDC and had 9 foot probes. Reading the comments several users cut the probe wires and extended them accordingly to suit. I think they were less than 10 bucks each, so I bought 3. I made a bracket to mount all 3, one for supply air, one retun and one outside ambient. I found a small power adapter I saved from something that had the right voltage, and I used 24 gauge wire to splice into the probe wires. I'm sure they may not be perfectly calibrated with the added wire, even if they were in the first place. I ran the outside probe following the line set for the HP and mounted it close to the condenser and out of sunlight as best I could. So at a glance, it's easy to see how the unit is heating/cooling compared to the return air temp. Once I saw I wasn't getting a full 20 degrees differential, changed the filter and it came right back.
Gadgets are cool!
 
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chinboys

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Joined
Jun 20, 2011
Messages
434
The temp readings are just one perspective of how your heat pump system is working.

As a rule of thumb, you also want your evaporator blower to run at 400 ft3 per ton of cooling.
Then you have to make sure you have the right ducting sizes and register opening to make use of the above rule.

Pressure readings on the liquid and suction lines and its subcooling or superheat temps also show your system is working.

Then measure the steady state amperage draw on all of the motors (evaporator or inside blower, condenser fan, and compressor) to see if they are normal or above.

It's too bad there doesn't exist a device to do this for residential use.
 
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PopcornSutton

Well-known member
Joined
Jun 10, 2024
Messages
784
Location
Northern Tip of VA
You are correct on all these items, but that all should have been designed/checked on installation. I clean coils once a year, change filters way more often than once a month. I like the three temps on all the time, easy to see were things are as outside temps change.
 
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fitter30

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Joined
Jun 23, 2019
Messages
2,976
Location
Peace Valley,mo
chinboys said:
The temp readings are just one perspective of how your heat pump system is working.

As a rule of thumb, you also want your evaporator blower to run at 400 ft3 per ton of cooling.
Then you have to make sure you have the right ducting sizes and register opening to make use of the above rule.

Pressure readings on the liquid and suction lines and its subcooling or superheat temps also show your system is working.

Then measure the steady state amperage draw on all of the motors (evaporator or inside blower, condenser fan, and compressor) to see if they are normal or above.

It's too bad there doesn't exist a device to do this for residential use.
Click to expand...
Every manufacture publish tech information manual on all the furnaces and ahu's and have external static pressure readings to cfm. Then you know what the furnace cfm is producing. Subcooling and super heat is for expansion valve systems. All that is needed other than hand tools are gauges, surface probe electronic thermometer and pt chart. Clamp on amp meter that can also read vac. Don't recommend taking refrigerant reading unless there is a problem all residential units use schrader valves to easy to have a leak or problem hooking up the hoses.
 
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