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Heating, Air Conditioning, Fridge, HVAC/Compressor Amperage Overload Only in Cooling


I purchased a house with a closed loop water to ground heating/cooling system with a scroll type compressor.

The compressor would shut off occasionally when I moved in. It is either a 3 or 3.5 ton unit.  AC guy came and found out it was tripping off on suction pressure.  Adding a lot of refridgerant thinking it was low barely boosted the numbers but kept it running.

He then came back and replaced the top diaphragm portion of the expansion valve and in the process lost some refrigerant.  This "fixed" the problem and the suction head pressure to just slightly below normal.  He was very hesitant to try and add any more refridgerant was it was extracting great heat from the water loop (table in instructions gave around 4-6 and it was extacting around 7).  Ran great all winter.

So it was finally time to fire up the AC yesterday.  It worked great for a few minutes and then I noticed the compressor shut off.  I restarted the system and again after 2-3 minutes the compressor shut off.

I am an engineer so I was doing some troubleshooting myself.  Water temperature difference was about 13 degrees.  New air filters installed.  Measured the amperage to the compressor and it started out around 7-8 amps and slowly climbed to about 17.5 amps over the 2-3 minute period when it finally would throw the overload. Max sustained load labeled on the compressor is 16.1 amps.

I also tried to measure the temperature of the compressed refrigerant line as it exits the compressor with a touch probe and was getting about 150 degrees.

Out of curiousity I put it into heating mode and it ran fine.  Amperage settled out around 11 amps.

I called my HVAC guy and he seemed to be stumped on this one and said he would have to research it a little.

What are your thoughts of the problem?  Would too much refriderant cause such a situation.  We really have no idea how much of a charge is in the sytem.

Sorry for the delay.  I did not see or did not get the email you had posted a question.
A system that is overcharged can cause all sorts of issues, including high amp draw and high discharge refrigerant pressure.  Package units such as yours should have a refrigerant amount listed on the nameplate or in the manual.  The charge has to be weight in and needs to be as close to exact as possible.  If the unit is not running correctly with the proper charge, then the problem causing the malfunction has to be fixed and adding refrigerant is not the answer.  

I do not know what the water delta T is suppose to be, but 13 seems a bit high.  I would also have to take multiple temp readings to get a better idea what could be going on.  


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Craig HVAC Expert


I have been in the HVAC field for the past 18 years. I can help with most HVAC questions. I work on commerical buildings for the most part, and have yet to find anything I could not troubleshoot and repair, when repairable. I work on small 1 ton units to a 2500 ton chiller. Troubleshoot air flow, elect, and control problems. I attend regular classes to keep up with the latest and greatest.


I work on commerical sites, hospitals, gov't buildings. I can troubleshoot just about anything in the HVAC business.

5 years trade school, VFD training classes, Liebert factory training, some York and Trane factory training.

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