cap tube woes

[tygerof2]

I've been working on a domestic refrig/freezer (20 yrs. old) with r-12 and a cap tube. Can't seen to get it charged right. Maybe a clogged filter dryer? Suction line frosted up and suction pressure way low- 15#(225#on high side). I've consulted several sources that say if its frosting up, you've overcharged the unit. Anyone have some good tips? Thanks.

[refrige-nate]

suction line frosting up could be a lack of air flow across the evap also. what are you using to charge? cap tubes are critically charged systems and have to be charged within plus or minus .5 of an ounce by weight.

[tygerof2]

I'm using a TIF brand digital scale. Weighed in 6oz. as the name plate said I should on the unit.

[pecmsg]

What refrigerant are you using?

[jackpiner]

15# suction & 225 # high side! Way overcharged. Res. refigerators run a low suction. Remember the freezer is the evap. with very little airflow.

[tygerof2]

The refrigerant is r-12 and I'm getting the suction pressure down to 10# now. There is very minimal frost on suction line now. Inside freezer box is 8 degrees/ refer box is at 40 degrees. However, the high side pressure is still over 200#. Could the filter/ dryer be plugged?

[TGoodrich]

If the filter-drier was obstructed, the suction pressure would likely be in a vacuum. The suction pressure should be near zero PSI. 10 is still too high. As long as the airflow through the evaporator is correct, the suction line should not be cold enough to frost. It sounds like it is slightly overcharged. You should not be connecting to the high side on a small system like this. The amount of liquid in the charging hose is significant. Did you evacuate the system prior to charging? The high suction pressure will cause the head pressure to be high also. But make sure the condenser is clean too. If the freezer is nearly down to temp, release refrigerant in very small increments and allow the system to balance, until the suction line does not frost. The suction pressure should be just above zero. It is very difficult to accurately weigh in the charge with digital scales. It's hard to account for the amount of refrigerant in the hoses, and it makes a difference whether it's liquid or vapor.

[rayr]

If you have frost within 6" of the compressor when it shuts off on set point, it is overcharged. If it frosts all the way to the compressor, remove just a lil bit of refrigerant. Trust me, tried and true over many decades.

[tygerof2]

Thanks all for the help. Yes, I did evacuate the system, even triple evacuated, nitrogen, the whole nine yards. I put the service valve on right after the compressor, which may have been a mistake because it sounds like it should've been AFTER the condenser. That was where the old process tube was on the original install. I do have good air flow across the coil, so I think that can be eliminated. So, are you saying the suction pressure should be near zero? Wow! Has anybody put too much faith in those electronic sight glasses? I tried one of those too. Sort of a hit-and -miss instrument. Thanks for all the input. :)

[ReferTroop]

I've found suction somewhere between 9-2 PSIG with R-12 is good, depending on manufacturers who like to put the least amount of cost into the product and run everything close to boarder line as far as size of compressor, condensor, etc. let the heat load come down to normal operating conditions which could take hours and see how the head pressure is then. Don't know what type refrigerant your recharging with but MP-39 always runs a higher head, I like HotShot ( R-414B) which seams to run a slightly lower head and definatly lower suction.

JS

[deckhanddave]

I've been working on a domestic refrig/freezer (20 yrs. old) with r-12 and a cap tube. Can't seen to get it charged right. Maybe a clogged filter dryer? Suction line frosted up and suction pressure way low- 15#(225#on high side). I've consulted several sources that say if its frosting up, you've overcharged the unit. Anyone have some good tips? Thanks.

suction/low side should read less then 2 psig with r12, 134, 409a or 414b (assuming this is less then a 20 cubic ft domestic refrig). make sure the condensor is clean and evap fan is working. If the filterdrier is warm (slightly above ambient temp) then filterdrier is ok, if it feels cold the system is plugged. Make sure evap is not a big block of ice which could mean defrost issue?>