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Old 08-06-2011, 07:28 AM   #1
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Refrigerant Problem


I'm not certain what's going on. I've cleaned the condenser and the temp dropped a few degrees, supply. The suction pressure is throwing me off. It's higher than normal, in the 90 psig range. The high side is at about 230 psig (r-22, btw) which by all accounts would be considered low.

Those pressures are coming from 120 low over 310 high before condenser coil cleaning.

When I run a water hose over the condenser the pressures drop instantly but then climb back up, low side to 55-60 and the high side to under 200. Seems to want to stabilize back at around 90 over 230. I'm attempting to charge the unit while the water hose is running over the condenser coil and it seems to be working as I've dropped a few more degrees supply and the head pressure is slowly rising while the suction is staying at that one spot each time the system stabilizes.

Originally I thought that the refrigerant in the condenser was having a hard time condensing and perhaps it was but I'm now wanting to believe that the high side is right, it's just still low on refrigerant but again, that low side without the water running on the condenser being higher than normal is throwing me off.

Any ideas?

So far between a condenser coil cleaning, the evaporator already being clean, sealing the transition from furnace to evaporator (which was leaking a lot of air in the attic) and reinsulating about 1' of exposed suction line in the attic at the evap suction line as well as adding a few oz of R-22 while running the water over the condenser and dropping the suction pressure to 60 psig I've dropped the supply air temp 6 degrees to at the moment 68f, which is still not good enough.

Thanks.

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Old 08-06-2011, 07:43 AM   #2
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Refrigerant Problem


what is the SEER and how old is the unit. is it a recip comp. your valves are worn or damaged if it is. compression ratio should be at least 3 to 1. your compressor is literally not pumping. valves are not seating and you are getting crossover from the discharge into the intake. possible with a scroll if the scrolls are warped or bent from liquid slugging.

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Old 08-06-2011, 07:58 AM   #3
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Refrigerant Problem


never charge the unit with a water hose running on it... your going to have an overcharged machine with no hose... R-22 runs 260/55 on the hottest of days with a clean condenser. take the inlet air temp on the condenser DAYS TEMP add 30F to that on the inside temp ring on the hi side guage that is a general goal when charging...18F split is typical on the furnace READ at the furnace filter and discharge duct..is your return tight from the space into the unit sucking of any ait on the return is going to kill that 18F.check under the unit where the ducts connect both sides...they usually tape it and if ends up drying out flapping supply or drawing air in....back to the charging grab the liquid line on the hottest of days should be warm to body temp with again on a clean condenser...design 10F rise air in air up into your face...are you purging the freon line before adding freon on that suction side.the liquid line is maintained 3-4 rows up from the bottom of the condenser from where it is connected to...the state of the HI side changes into liquid with that heat blowing up in your face but the pressure is close to the same into the furnace.....like a garden hose nozzle pressure drop within that furnace and it gives you 40F on the evap so you can see how important the return is tight and the only place you want the supply to be is at the register...check back later for results..filter clean squirrels on the fan section clean of dust dirt?

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Old 08-06-2011, 08:50 AM   #4
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Refrigerant Problem


How about superheat and subcool numbers doc? I suspect a wide open txv causing liquid back to the compressor( which can not compress,hence the poor compression ratio).
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Old 08-06-2011, 09:46 AM   #5
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Whats the return air temp at the evap. Whats the super heat and sub cool? Whats the outdoor temp. How much air is moving through that evap coil. What metering device does it have? Are the condenser and evap coil a ARI/AHRI rated match?
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Old 08-06-2011, 05:32 PM   #6
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Fixed orifice.The valves being bad are something I hadn't thought of, the crossover. How does that work? Are we talking service valves that simply open and close to the compressor/line set, one valve per each line? How would that allow crossover? Wouldn't that just simply not close off or open each line if they were bad?

The head pressure was rising, went from 200 to 230-ish, as I was adding refrigerant so the unit was pumping but can't say how well. The low side stayed a bit high, at one fixed pressure, 95, and wouldn't budge.

At that point all I was concerned about was dropping the suction pressure and air temp as something was definitely wrong. I stopped with the refrigerant afer only a few ounces as I didn't want to overcharge it especailly without any numbers, took an inside supply air temp and called it a day on that one as I had to go install a condenser fan motor across town and it was already 8 in the evening so at this time I have no numbers to give.

I'm going back tomorrow on my own time to figure this out so that's the reason I'm asking for the help, for when I go back, what to look into and hopefully without opening the refrigerant lines. I thought it was possibly a restriction and that was the original reason for the water, to see if the pressures changed and they did so no restriction..?

I'll document all numbers and temps tomorrow.

Thanks.
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Old 08-06-2011, 05:35 PM   #7
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Unrelated, from today to give you an idea of the ambient and pressures I'll be running into again tomorrow.


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Old 08-06-2011, 06:16 PM   #8
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Shield the probe from the sun so you get a true ambient air temp. radiant heat doesn't effect the condenser like it does your temp probe.

If your actual outdoor air temp was 105, 320 head would not be out of line on older equipment.

There is a good chance, that the unit was already over charged when you got to it. Recover, and recharge by weight.
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Old 08-06-2011, 09:20 PM   #9
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I talked to the home owner just now, said it cooled well during the night and for a while into the mid day (100+) and then it couldn't keep up. He has the stat set at 74 and it went up to 79. Bi-level two system home, one up and one down. This one is for the downstairs and is the bigger unit.

Can I ask to all you guys, with the minute info I've provided, where would you start if you were going to figure this out? Is a target superheat even worth the time with these off pressures? Would recovering the refrigerant and putting new be plausible, with a solid vacuum? I'm not sure if there's air in the line, not sure how to tell.

I'm thinking I need to at thevery least pump it down and check the piston and the ll drier for blockage. I did check temps across the ll drier (139) and it was the same on both ends so I didn't think there was a restriction.

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Old 08-06-2011, 09:23 PM   #10
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Recover, and weigh back in a virgin charge to data plate spec.
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Old 08-06-2011, 09:25 PM   #11
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I would suggest you study the internals of a reciprocating compressor. There is a discharge valve and intake valve just like in a car engine. If you do true refrigeration like Beenthere does and myself you know what a valve plate from a compressor looks like. In trade school they had us lap/grind/reseat the valves and the plate. Google: reed valve.
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Old 08-06-2011, 09:31 PM   #12
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Quote:
Originally Posted by beenthere View Post
Recover, and weigh back in a virgin charge to data plate spec.

That is what I would do. You need a clean reference point to start from. May want to do it in the coolest part of the day whenever that is.
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Old 08-06-2011, 09:39 PM   #13
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Refrigerant Problem


I hope the charge specs are there. It does make sense to have solid ground to begin from. Thanks guys.

This is the condenser but you can't tell much. I can go the truck real quick and get the make and model/serial number from the service ticket. I do believe that's an old school Copeland Scroll.



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Old 08-06-2011, 09:44 PM   #14
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Looks tall and skinny like a scroll. We don't have a lot of old scroll units here yet so I don't know what characteristics they will have when they get over 15 yrs. I do know of one brand of recip that loses it compression from cheap valves/wear etc around 15 yrs old and you start getting higher suction and lower discharge. Scrolls don't have valves to wear but I/we don't know if they wear the scroll or could lose capacity from internal damage to the scrolls. Perhaps some of the other guys can shed light on that part of the story.
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Old 08-06-2011, 09:51 PM   #15
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That squirelly, squiggly line on the compressor cap is the Scroll symbol, used to this day. Plus it is tall and skinny, typical of a Scroll.

I do need some edumacation on reciprocating compressors and their valves, though. I hadn't nor have a clue, I never see those.

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