Author Topic: A/C Troubleshoot  (Read 3556 times)

Offline walker

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A/C Troubleshoot
« on: June 03, 2015, 08:42:46 PM »
I've had this problem on about 3 or 4 Rheem 14AJM units in the past 2 weeks I've got called out to look at.  Everything seems fine except for the subcooling.

all brand new units 1.5 and 2 Ton units with a copeland scroll compressor.

I'm getting what seem to be good pressures, 125/225PSIG on not too hot days between 70-80 outside roughly.

superheat runs around 10-13, but I cannot get any subcooling going on, it hovers 0-2.

I'm getting normal delta T around 20.

What could be my issues with these units?


Offline harshal

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Re: A/C Troubleshoot
« Reply #1 on: June 04, 2015, 05:31:29 AM »
If u have txv at the coil,u charge the unit by subcooling method.if u have the piston type coil then should charge by superheat method.u would need wet bulb measurements for superheat method.I always measure both for proper charge.

Offline walker

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Re: A/C Troubleshoot
« Reply #2 on: June 04, 2015, 08:20:17 AM »
Yes I'm well aware of this.

The issue is the charge is correct. They are both brand new units proper charge.  I can't get any subcooling out of them.

I've even overcharged one of them and still no rise in subcooling.

I've also made sure the bulb is firmly attached in the correct position.

Any other ideas.

Offline harshal

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Re: A/C Troubleshoot
« Reply #3 on: June 04, 2015, 01:20:54 PM »
I wouldn't worry much if I am getting good temp diff across coil.sometimes u have to add good amount of refrigerant to get proper subcooling as these high seer unit woulud hold lot of refrigerant in them.

Offline walker

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Re: A/C Troubleshoot
« Reply #4 on: June 04, 2015, 01:23:01 PM »
It seems good but it isn't.  The cx stated that the A/C wouldn't keep up, and ran all day to drop 2 degrees and wouldn't get any lower than 23 in the house.  15 not bad but it also it great.

Offline Admin

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Re: A/C Troubleshoot
« Reply #5 on: June 04, 2015, 01:43:42 PM »
There's an industry wide problem, mostly with Copeland scroll compressors, which can damage the TXV's.  Essentially there's a rust inhibitor in the compressor that is causing a chemical reaction with the POE oil in the 410A refrigerant.  This causes the TXV to become restricted.  One of the symptoms listed was insufficient cooling.

Lennox sent me some information on this.  I will scan and post the document tomorrow.  There's a procedure to follow.

You should also contact Rheem.  I believe your AC's have Copeland scroll compressors.

I just dont understand how you have a temperature drop of 20F but can't cool the house.  I rarely install TXV's and have not run into this problem yet.

Offline walker

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Re: A/C Troubleshoot
« Reply #6 on: June 04, 2015, 01:46:23 PM »
Yes I'm well aware that issue from last year. Changed about 25 of those txvs.  Most of time the symptoms on those txvs is the subcooling would be just fine but the suction pressure would be quite low, usually stuck sound 80 or 90 lbs no matter much r410 you dumped in to the system. I'll keep an eye on these A/C going forward, was just wondering if I'm over looking something.

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Re: A/C Troubleshoot
« Reply #7 on: June 04, 2015, 01:53:37 PM »
Are the TXV's adjustable?  I think they turn counter clockwise to increase subcooling.

Usually low subcooling is either an inefficient compressor or under charged system.  It doesn't sound like you're undercharged and usually an inefficient compressor causes high superheat.

I would perform a pump down test.

Start the AC and close the high side service valve.  Once the suction pressure drops to 10 psig, stop the AC.  It's normal for the suction pressure to increase slowly, but if it increases over 12-15 psig/min you can be sure the compressor is leaking internally.

Also is there a chance the AC is undersized?

Offline walker

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Re: A/C Troubleshoot
« Reply #8 on: June 04, 2015, 01:56:52 PM »
Good call, I'll try that out on the next one I see. I have a feeling it's install related. Maybe they are cracking the liquid  line first and not the suction and the oil is getting sucked back to the txv or something.