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Question DetailsAsked on 1/27/2018

Heat pump runs emergency heat all the time. Two estimates! I do I know which part I need to replace .

I have had two companies come out to check my unit. The first replaced a fuse and said it now needs an EEV Control Board. The second company said it was leaking freon and had oil on something. Both estimates are high. What would everyone suggest?

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1 Answer


OK - when nfinishing this and proofing it, I see I got pretty lengthy and addressed a lot of, for a homeowner, complex issues - so if you get bogged down and can't take it in, try just scanning first before trying to wade through the detals.

You have a tough call situation which unfortunately commonly comes up with HVAC jobs - two "experts" saying different things. And both probably talking about $500 or maybe much more for the repair - and if it is leaking you may not know WHERE yet, so if it is a coil leaking that could add $1000-2000 range (including gas refill) for a normal household sized unit, which might push you (especially if a freon/R-22 unit) toward a new unit rather thann repair.

BTW - you can find a lot of previous questions with answers addressing the Freon phaseout costs and some times very high costs or recharging a Freon based system, and on the repair versus replace issue, in the Home > HVAC link, under Browse Projects at lower left.

Here also are links to a few articles on heat pumps and how they work, in case you are not clear on their functioning or on what the auxiliary heating and "emergency" heating functions are - might read them first before getting into my diagnostic possibilities below:

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One preliminary question, keying back to the articles above - if your outside temperature has been part of the recent nationwide cold snap, so it is below the effective heating range of your heat pump, is it possible (assuming the unit was actually running and the gas was not low pressure in the unit) that the emergency heating coil or gas burner (actually auxiliary or supplemental heat) is running just because it is too cold for the unit to turn out enough heat to keep up with the demand ? For instance, it might be able to maintain 60 degrees when it is say 30 outside, but not 65 or 70. This can happen because the unit is just undersized for that temperature - i.e. you are experiencing outside temps below the design capacity of the unit. Generally speaking, the unit will be able to handle a certain difference between inside and outside temp - generally speaking (to simplify it) once the unit is putting out all the heat it can, drop the outside temp 10 degrees and the inside temp it can maintain will also drop 10 degrees.

This inability to keep up can also can happen in windy conditions, where it keeps up OK in calm conditions at a given outdoor temp but cannot provide the added heat needed to keep the house up to temp when you add in the much greater convective heat losses in windy conditions. Most heat pumps become relatively ineffective at heating below about 40-45 degrees outside ambient temp (air or ground temp, depending on whether standard air-to-air or geothermal unit), and commonly cannot by themselves (wthout the auxiliary heating) keep up with the heating demand on a normally built and insulated house below that temperature. Below somewhere around 25-30 degrees almost all heat pump units turn out very little if any heat at all and contribute little if any of the heat produced - the auxiliary unit is doing basically all of that, and if electric can run up quite a monthly bill keeping up during prolonged very cold outdoor conditions like much of the country has been seeing.


Also, another possibility - again reference the articles, but if your setback temperature (assuming a programmable thermostat) exceeds the "setpoint" temperature differential for the auxiliary heat to turn on, then every time the thermostaat reaches a period when the higher temperature is called for, the auxiliary heating will come on until the house comes up to (depending on unit design and thermostat design) either that temperature differential or the desired temperature being called for by the thermostat. Say you keep the house at 70 when home but use a setback to 65 when away or at night. If your unit or the thermostat is designed/set so the auxiliary heating comes on at a say common factory setting number of a 4 degree difference between temperature at the thermostat and the desired temperature, then when the time for the thermostat to call for 70 degrees before you come home or wake up would cause the auxiliary heat to turn on when the desired temperature called for by the thermostat jumps from 65 to 70 degrees, EVEN IF the heat pump could gradually get to that temperature by itself. Some smart units will shut off the auxiliary heat as soon as it hits or exceeds that setpoiint difference - so would turn it off at 66 or 67 degrees actual temperature, others leave it on until the temp reaches the actual temperature called for, then when the unit next kicks on because of a call for heat may leave it off - IF the thermostat delay setting is less than the setpoint difference.

This is where it gets a bit confusing, regarding the above thermostat decision process (which can be in the unit or the thermostat depending on design - usually thermostat controlled). But I will try to make it understandable - yuou can get into a situation with the unit fighting with itself. Say for instance the auxiliary heat "kick-on" setpoint is 3 degrees difference between actual and desired temperature - so for this case auxiliary heat would kick on anytime the actual temperature at the thermostat dropped below 67 in the above 70 degree call for heat case. Now, with more sophisticated programmable thermostats which allow you to define how much the temperature can drop before it actually turns the heat on, say that was set for 4 degrees - the allowable household temp variation before the HVAC system comes on to adjust the temperature.

So, in this case, the thermostat would let the house drop to 66 (or 65 depending on whether the thermostat operates on "equal to" or "greater/lesser than" logic) before calling for heat. In this scenario, with the auxiliary heating set point set at 3 degrees but the cycle setback for the thermostat set at 4 degrees (or maybe built-in at that) you would have a situation where the auxiliary heat would ALWAYS come on when the unit started heating, because the cycle setback lets the temperature drop below the auxiliary heating set point before it turns on. This situaiton can drive homeowners and techs crazy if they do not know about it, and can result in $500-1000 monthly electric bills if using electric auxiliary heating, because the auxiliary heating component is doing almost all the heating - especially when it is cold outside so the heat pump is operating with low heat output capability. Highly programmable thermostats like the NEST or Honeywell Total Climate controllers are the ones where this sort of situation occurs most often, but is also popping up in thermostats and HVAC controllers which run off a whole-house computer control system. I have seen/heard of cases where confusing setpoints and setbacks and delay lags overlap to the point a heat pump will put out heat, suing the auxiliary heating system, then detect the higher temp and realize that is above the A/C setting, and turn on the A/c - alternating between the two, heating and colling and then immediately reheating. Most electrical/simple programmable thermostats have an option between heating, fan only, and A/C so cannot do both at once, but some of the electronic ones totally control the system and decide for themselves whether to heat or cool - so have a setpoint and setback situation where say one setback period is for 70 degrees, if the A/C is for example set for 65 degrees, while the thermostat is calling for 70 degree heat is may also be saying it is over 65 so the A/C should be on, so it cycles back and forth between them - with the heat coming on during the A/C cool down interval (commonly 5-10 minutes before it will kick back on). The same thing can happen during the summer, and with variable auxiliary heating setpoints I have seen at least one system where the auxiliary heat was running at the same time as the heat pump was producing cold air in the A/C mode - and many heat pump control boards do not prevent this sort of confusion. Heardof one case with $3000 monthly electric bill on a new home because of that sort of fighting over heating/cooling because of overlapping set points and setbacks and delay lags.

Similar thing can happen in A/C mode with multi-speed units - wrong setpoint definition can result in the unit always running at max output rather than the more efficient lower power, even if the lower power would be adequate to bring the temp to where it is desired to be.

An even more complicated set of conditions can occur when the outdoor or indoor temperature sensor fails or misreads or is located the wrong place - causing incorrect readings of the operating and ambient temperatures. I have seen cases where the outside sensor was put near the air handler or coil or inside insulation so it read a temperature which was not representative of the actual conditions - keeping the unit from coming on when it should have, or causing it to shut down prematurely because the unit was heating up to sensor or cooling it down improperly.


Now - what I would suggest:

I would first get clarification from the first guy whether he checked the refrigerant pressures - i.e. did HE detect leakage ? And specifically what was burned out on the EEV system, and if he says the board is fried, was that because of oil from a leak or did the fuse and board blow because another componetn like the valve stepping motor failed ?

On the second guy - find out if he tracked down where the leak was, and where the oil (which likely came from the leak unless the compressor is leaking oil) leaked, whether he actually measured the static pressure in the unit to determine if the unit was low on refrigerant or not or just assumed tht was the probl,em because operating pressures were off (which could have been caused by failed EEV system), and whether his estimate includes replacement gas or not and if not, how much additional for that.

The problem you have, is if the unit was malfunctioning because of improper pressure in the unit when operating, that could have been because of an EEV (electronic expansion valve) board failure - could also be because of a stepping motor faillure on the valve, or the valve itself, or because of leaked off refrigerant making it so the unit cnanot maintain proper operating pressures. Those parts along cost about $250-450 for the board (depending on make/model) and about $100-250 each for the others.

If he changed a (presumably failed) fuse something clearly overloaded - but could be one thing overloaded and took out not only the fuse but also the board, or could be just the board - so unless the first guy did a function teston each component AND power/continuity trace he might or might not actually know the actual cause - and in the worst case he replaces the board and immediately fries the new one because the problem is a failed stepping motor or valve or one of the several sensors shorted out whichk then shorts out the board, so it takes an experienced tech to know not only WHAT failed but also to check out (before replacing parts) if that failure was possibly the result of another failure in a different component. Not real tough to do, but most techs these days are not trained in tracing faults, especially in electronic systems, and just get into the mode of "replace it and see if that was the problem" - which can get very expensive for you.

I remember one system where the tech changed out pretty much every electrical and electronic component in the system TWICE and still came up with a non-functioning unit - turned out the transformer had shorted internally due to a slow drip on it so it was putting out about 60 volts instead of the 24V the system was designed for, so after it ran for a bit it fried electrical/electronic components. The first tech was up to about $3000 in bills, on a unit costing not much more than that for a total replacement, before the owner called it quits and called another HVAC company, who caught the incorrect voltage changed out the $25 failed transformer (plus the other now burnt-oput again components) - because the first tech never checked voltage at the failed components.

On the low gas diagnosis - if it was leaking (and perhaps the leak was at the valve so the oil in the refrigerant leaked onto the EEV board and fried that in the process, so both techs might be right about their finding A source of failure) - but without tracking down the leak and fixing it first, just putting new refrigerant in it (assuming it was actually low on refrigerant and it was not just improper pressure in the system when operating because of a failed EEV/EEV board) would just be throwing your money away because it would just leak out again in days, weeks or months. Not to mention being illegal because knowing discharge of the common residential refrigerants by putting it into a known leaking system is illegal.

And if a coil (condensor or evaporator) is what is leaking, unless just at the connection fitting, they generally cannot economically be repaired (and almost noone does it these days anyway), so the issue of possibly $250-500+ to refill the unit with gas (assuming it has pretty well drained out) plus $1000-1500 for a coil replacement or $1000-2000 if the compressor is what is leaking, could put a whole different light on the repair-versus-replace decision. Worst case, you could be talking a failed coil (so refrigerant and lubricating oil leaked out) causing overall unit failure due to overheating (because the refrigerant both cools the compressor as it passes through, and carries the lubricating oil with it) so you could be looking at $500 or more at the EEV if the board is fried from the oil, PLUS $1000-2000 coil if the proximate cause is a leaking coil or compressor - plus $1000-2000 for a new compressor, meaning total unit replacement would almost certainly be the most economic solution in that case. Without checking the condition of the refrigerant and oil (by chenging the filter/drier and seeing if the oil is burnt/scorched) one would not know if there might be a leaking coil, fried EEV, AND fried compressor - basically all operating parts failed, for which total unit repalcement with a new one would be the smartest solution.


Hopefully talking to them about the details of what they find will clarify which is right - evidently, since you called a second one you did not trust the first answer so that might complicate things too. And of course, calling a third one (at probably $100 or so a hit) might just give you a third answer.

Answered 2 years ago by LCD

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