Greek Mystery

Tony Pullen

System on a mobile home with compressor shorted to ground. Replaced with the correct size comp for the condenser and before charging decided to remove and clean the evap. Upon inspection, discovered that it was a 4 ton evap that had been running on the 3 ton cond. Replaced evap with 3-ton coil and orrifice...weighed in correct charge...pressures weren't even close in cooling (25 suction and 50 head). the guy working for me assumed that his scales were wrong and continued adding r-22 until he got the pressures close to where they needed to be. unit worked well until....switched to heat mode and head pressure sky-rocketed..kicked out on hps....removed 6 extra lbs of freon and works correctly in heat mode, but low pressures in cooling (25 low and 60 high) I am thinking something going on with metering device in cooling....any suggestions, or am I simply missing the elephant in the room?

beenthere

Correct size compressor for the condenser? Often a 3 ton condenser will use a 28,000 BTU compressor. So what did you put in. The nominal rated/listed indoor coil was probably the right coil. The new nominal rated 3 ton you put in is probably too small.

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Tony Pullen

no, it was a full 36000 btu

Tony Pullen

I should mention that the outdoor temp that day was 65 degrees fh and the indoor temp was 68, so......on a hot day the pressures might not be too far off???? what do you think? btw, thanks for the response!

beenthere

Could still be too small of an indoor coil as part of your problem.

Was the LLFD changed out?

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How many times must one fix something before it is fixed?

Tony Pullen

would not have installed the comp. without a new filter/dryer

Vaporx

IMO it's difficult to evaluate fixed metering system numbers with ID and OD temps that low. Condenser coils "over condense" producing low condensing temps and low head pressures which generate low metering rates through the piston, which generate low suction pressures... And without a superheat reading, the evaluation is more difficult.

In my travels, mfg homes have more often than not, suffered from low airflow through the indoor coil. And not so savvy service techs tend to "correct" the resulting low suction pressure by overcharging the system, which may eventually explain the shorted compressor motor windings.

You can wait for a warm day to better evaluate the operation, or block the condenser coil to raise the head pressure to a more realistic number...but I'd bet airflow is the problem.

Tony Pullen

thanks vapor....airflow could be an issue, but if it is, it was built into the home from the factory...and that is VERY possible, but I think maybe it was simply because it was cool that day. works fine in heat mode, so gona wait and check the unit on a warmer day.

ironpit

could you run the furnace to get the inside temp to about 80 and block the condensor coil off to get a better read?

Vaporx

That would improve the "conditions of the test".

ironpit

true. But isn't that the way units are tested in R&D at factory, to simulate field conditions?

Vaporx

I have no idea what they do at the factory...except maybe wait for the glue to dry.

beenthere

No, they don't block off the condenser. They use environmental chambers whee the maintain that condition.

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How many times must one fix something before it is fixed?

ironpit

I didn't mean literally. I was , I guess rather poorly, refering to climate or conditions control such as what beenthere stated. Sorry for the mislead.