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Mismatched heat pump

I am running a 3 ton condensing unit matched with a 2.5 ton evaporator. what trouble will I have later on. I also use a hydrocarbon refrigerant charged at 10 degrees below ambient. HELP PLEASE

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This will create an overload on the evaporator, and you will definitely see issues along the way - overheating, higher electric bills, poor cooling, just to name a few. In other words, they waste money, electricity, and dont provide the comfort expected.

Best get them matched to avoid future issues which can result in expensive repairs later on

Here is a better explanation I found online:
"One gets higher SEER ratings through several avenues. One of the easiest is through a larger coil. Look at R22 3 ton units at 10 SEER and look at the same tonnage at 13 SEER and you cant help but to notice how much larger the higher SEER is. Greater coil face (hence the larger unit) means more refrigerant necessary to fill the thing. Secondly, higher SEER is also achieved through lower compression ratios (the ratio of absolute pressure discharge divided by absolute pressure suction). Obviously the suction pressure has to remain at a certain pressure/temperature. Thus, we need to lower the discharge pressure - remember the lower the compression ratio (the lower we can get the top number) the more efficient.

If your new coil outside is larger it needs more refrigerant. If your indoor coil is fed by a fixed orafice and the outdoor pressure is lower, the evaporator pressure will be lower without the help of a TXV metering device (the metering device is yet another way to get higher ratings along with Scroll compressors and variable speed motors). Considering that your outdoor unit is larger (needs more refrigerant) and most likely your metering device is not TXV (cant adjust for the lower compression ratio and lower high side pressure) your unit is most likely acting under charged due to the mismatch. Remember, your fixed meter device is looking for a certain pressure behind it and the newer higher efficiency condensor may not provide it. Your unit may very well have a leak; however, I would look to the mismatched equipment first.

Everyone has their opinions on matching coils and changing the evaporator coil and metering device when the condenosr is changed out in a higher SEER rating. My experience from talking to the manufacturers and reading the test results of units PURPOSELY mismatched and tested for performance lead me to make sure they are matched. The test results I have seen show that mismatched equipment will not even give the 10 SEER rating of the original unit - they waste money, electricity, and dont provide the comfort expected.

HVAC is like a see-saw on the playground. Its a balancing act to get the right action out of it. Saying X-tons condensor mismatched to X-tons evaporator is the same as having one real skinny kid on one side of the see-saw and a one really fat kid on the other side. Both are 3 years old - just like the unit halves are both the same tonnage. The 2 kids are not rated or matched the same for capacity all things considered. While its funny to watch on the playground, the same is not funny in your house when you are paying alot of money for equipment and the service it is supposed to provide. Unfortunately, chances are good the unit will not perform to any standard that is worth while in its current configuration."

Posted on Jun 11, 2008

  • Swilin Sampson
    Swilin Sampson Jun 11, 2008

    If you found the advice I provided useful, kindly take a moment to "Accept" my solution. Should you have any further queries, please post back and I will try to assist you further as best I can..



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Well, it will go on the usual problem.. the lower the capacity and did not meet the standard will be the first got damaged/problem....-0r- it will also be the cause of unexpected shutdown of the whole unit...

let me know...

Posted on Jun 11, 2008

  • micromaster
    micromaster Jun 11, 2008

    like installing or somehow by example that you will buy a pair of shoes, of course you will not buy different size for each 9 1/2 for the right & 8 1/2 for the left... and in this i thinkyou will never get a good performance in walking or in runing..

    That's how..


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The temperature should be maintained within the specified range ,this may be done by the control units so check that carefully

Posted on Jun 11, 2008

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Well..this is a load variant issue. Depending on your cooling load, and the voltage input fluctuations(energy in does not equal energy out) you will have the air conditioning equivalent of a mismatched differential in a Jaguar.

If you can limit the coolant temperature range, via the thermostatic control, and keep a close watch on your fluid pressure/levels, you might get away with this.

usually, you want to have this arrangement in a reverse differential.

Posted on May 31, 2008

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