Heat Pump and Supplimental Heat

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Old 02-20-15, 07:23 AM
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Heat Pump and Supplimental Heat

I have a house that has 2 heat pumps, one for upstairs and one for down stairs. This past summer we had the whole upstairs system replace with a high efficiency unit. During this cold snap, it is running beautifully.

The downstairs unit is a 14 years old, 8 seer unit. This past week it has struggled to keep up with the cold weather. While our temperatures last night pale in comparison to other parts of the country, our buildings are not as well equipped to handle such low temperatures (5 degrees). Came down this morning and it was in the 60's down, while a toasty 70 upstairs. I have been monitoring the temps coming out of the vents downstairs at 72 degrees. Nudged up the thermostat early to no avail. I just went over and switched it to supplemental heat and suddenly, I get 100 degrees coming out of the register and the house is heating back up fast. Usual temp out of the register in my office is 80 degrees.

Isn't the thermostat supposed to automatically call for emergency heat if demand can not be met from normal operations. In the past, if we needed it a little more hot, as soon as you pushed the thermostat up, the emergency heat light would come on. I'm thinking the thermostat is wired wrong.

When the new unit was installed this summer, the assistant tech installed the new thermostat in the downstairs hallway instead of upstairs hallway. He had to remove, switch and re-install the old one downstairs. Can it be wired incorrectly that it doesn't call for emerg. heat?
 
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Old 02-20-15, 07:35 AM
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Isn't the thermostat supposed to automatically call for emergency heat if demand can not be met from normal operations
Usually when the differential is more that 3 degrees brings on the electric heat. Some thermostats require a jumper from AUX to E for the electric heat to work properly. Can you post the model number of your stat and tell us what color is on what terminal or even shoot a pic.
 
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Old 02-20-15, 07:36 AM
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You absolutely don't want emergency heat to come on. You want AUX heat to supplement the heat pump. He may not have it wired correctly to where AUX kicks in. We're in the same boat, but I have the plenum heater in the basement that supplements it quite well. If the fire diminishes, I can go past the stat and it is registering AUX heat. I build back up the fire and it goes off.

Emergency heat is for when the heat pump fails and you will die from the cold, IMO. Your power company will love you for having it on, however.
 
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Old 02-20-15, 07:55 AM
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This is the Heat Side of the thermostat - It is a Honeywell circa 1985

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Here is the cooling side

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Here is the panel under the mercury floats. This picture is from the one that was removed from upstairs and not the one for downstairs. However, they are virtually the same unit.

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Old 02-20-15, 08:08 AM
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Silly me, you probably need to see how the wires are on the actual wall unit. Figured it out after staring at the one on my desk. Try this one - It is a carrier unit which was probably original to the house as well.

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The one on my desk still has the wires attached as they cut it out from the wall. Look to be set up exactly the same except that black goes to X on my desk and to C on the wall.
 
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Old 02-20-15, 08:46 AM
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I'll let the HVAC pros comment on the wiring. Did Noah have this on the Ark?
 
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Old 02-20-15, 08:51 AM
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Cutting edge technology, gotta problem with dat? Motto - If it ain't broke you don't have to fix it, Although, I do have a certain market on mercury cornered.
 
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Old 02-20-15, 09:32 AM
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Aux heat and emergency heat are the exact same thing. Only difference is emergency heat over rides the HP. Looks like someone is looking up if you need that jumper. Lets see if that is it.
 
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Old 02-20-15, 09:35 AM
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They aren't the same thing, since Emg shuts down the HP. Aux runs and supplements the HP. I think a wiring diagnosis may help, not sure.
 
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Old 02-20-15, 10:11 AM
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Exactly that's what was said. Same heater.
 
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Old 02-20-15, 02:30 PM
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I would consider placing a jumper wire between W2 and E.

It is possible that a 15 KW heat strip is in use with W2 controlling 5 KW, and E controlling 10KW.

The W2 element may have failed or not be enough to supplement the heat pump.

A clamp on amp meter would be a great tool to prove operation of the heat strips when Aux heat is in demand.



It is also possible that the W2 wire isn't connected to the air handler at all.
 
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Old 02-20-15, 03:04 PM
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Your picture shows the air handler/heating unit, but are you saying to permanently jump from W2 to E at the thermostat? No work was done on the hair handler/heating unit. You are also saying make sure that white and gray are hooked up in the unit. Does the thermostat go to the air handler first or to the outside unit first and will the same color wires be present throughout? Thanks
 
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Old 02-20-15, 03:16 PM
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There may have been a jumper that wasn't put back on.

The t'stat wiring goes to the air handler where the outside unit is also connected.
 
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Old 02-20-15, 03:19 PM
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are you saying to permanently jump from W2 to E at the thermostat?
Yes. If W2 isn't making you comfortable, add E.


Does the thermostat go to the air handler first
Yes


will the same color wires be present throughout?
Yes. White should be white at the attic end and black should be black at the attic end.

If you have any splices between the 2 points it is usually just outside of the air handler. Take a picture of this splice if it is present.
 
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Old 02-20-15, 05:51 PM
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Final questions I guess, Is the line I will be jumping "LIVE" that I need to shut the breaker for the whole unit down first? Or is it like working on telephone lines where there is not enough energy to even give you a jolt.
 
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Old 02-20-15, 06:24 PM
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It is 24 volts AC at the thermostat. You can feel it if you are kneeling in mud outside but not when you are inside.

240 volts AC is present in the air handler.

If you short C to R you can damage a fuse or transformer in the air handler.

Trane, American Standard, Rheem, and Ruud were slow to start installing low voltage fuses to protect the transformer.

It is always safer to turn off the breaker to the indoor unit when working on your stat wiring.
 
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Old 02-21-15, 03:57 PM
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The jumper IS out in the air handler unit in the garage and not that the temperature is above freezing everything is fine. So I don't anticipate another cold event like this this year. Do you think that it could be the thermostat itself? I do have a spare.
 
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