Low Suction Pressure

[opey456]

I recently replaced the compressor in a unit for a customer. This is the third compressor in 3 years for this customer. This is the first time I have replaced it, other companies replaced the previous 2. After starting the compressor, the suction pressure would not rise above 60. The temperature inside the house was 85 degrees. After operating at that temp for 1 hour the evaportator coil began to freeze. I pulled and cleaned the evaporator coil, took the orfice out and cleaned it and there was a small piece of plastic at the bottom of the orfice. After reinstalling the coil and putting a new filter dryer in, and pulling a good vaccuum, there was no change. The unit acts as if the #92 piston is metering the refrigerant the correct way but I have never had to replace a piston due to that. Thinking of replacing coil or metering device but not sure if that will fix the problem. Just wondering if any of you have had this problem and any advice will be appreciated. Also, don't think it is an air flow issue, all the cross over duct is fine. Duct size is 12 in.

Model of condensing unit-Payne Model #- PA1OJA060000AAAA
Serial #- 1399E04588

Model of indoor unit- Model #- DGAT070BDF
Serial #- 990664386

Indoor coil- don't know the model # but know that it is a 5 ton coil

[Robert]

Hi,

Because this customer has now had 3 compressors changed out due to wrong reasons, my advice would be to find someone qualified to assist in resolving this.


No component should ever be replaced because you "think" it is the problem and you and 2 others should be paying for those 3 compressors, not the customer.


The word "think" is included in your post too much. In this business, the customer pays you to think until you know.


Then and only then, do you replace anything.


To know that 2 compressors had been changed out in previous 2 years and to then replace a 3rd and now "thinking" about replacing the a-coil or orifice , but "not sure" that is it either is wrong.


Sorry to be negative, but then again, that is what's needed here.


You came here for help and that's good, but do not replace anything more unless you are sure.

If you cannot reach that point, then admit it and walk away or find someone more experienced.


That customer should not be paying for on the job training.


There is most likely a blockage/kink between the compressor and evaporator somewhere, just have to find it.


I commend you for seeking help, just wish you had done so sooner, but better late than never.

BTW, yes it has happened and was due to different reasons, but always because of what I stated above somewhere in the system.


Test and make sure electrical is fine.

Test and make sure airflow is fine.

Recover,pressure test with nitrogen, vacuum with micron gauge and weigh back in correct charge.

That narrows down to what I said.


Did you blow through coil while it was removed ?



Take care and best wishes,
Robert

[opey456]

Well I'm sorry to think the coil is bad but i have already gone over the line set inch by inch thinking it was kinked somewhere.I also did recover the refrigerant and blow dry nitrogen through the system both ways. I then evacuated the system to 400 microns charged the system and had the same thing.My concern for the evaporator coil is that i did find the piece of plastic at the bottom of the piston meaning what else could be in the feeder tubes or the coil itself.

[opey456]

I commend you for seeking help, just wish you had done so sooner, but better late than never


This is my first time working on this unit i cannot help what the installer and/or previous techs did by apparently not keeping the copper clean and leaving the previous 2 compressors running with those pressures. All I'm trying to do is help these people who have already spent more money than they ever should have........

[Robert]

Who paid for the compressor you put in ? What was unit doing when you arrived for the first time ?

Thinking about replacing the evaporator coil without knowing for sure if it is the problem is adding to their money spent.


If you wish to help them, do so, but don't replace anything unless you're sure that will resolve it.


From your post, you replaced the compressor and obviously thought that would resolve the issue(s) and it didn't.


Fully diagnose and know before you replace anything.


If I missed something, fill me in, just going by what you posted.


Take care and best wishes,
Robert

[opey456]

I replaced the compressor due to it blowing the terminals out.After starting the new compressor up is when the suction pressure would not rise.The reason the last compressor blowed the terminals could be due to the last guy leaving it that way the homeowner said that it kept freezing up after he left . My concern for the Evap. coil is because i did find trash inside the coil......The piece of plastic i mentioned in the first post..........But i have blowed through the coil both ways and the whole system to no avail..But the feeder tube should have some lite frost on them when the unit is operating but they dont ...

[Robert]

Hi,

Ok, more info always helps. I would bring in a 2nd and maybe even a 3rd opinion on this.


The problem here is IF you replace coil and it still continues the same, customer will not be happy, so got to be sure here.


How are the coil fins ?


Blowing out system and isolating components for seperate testing/inspection is what I would do.


Go back over each step and if it comes to same diagnosis, that's where it is good to have a 2nd opinion.


Keep us updated please, not an easy one from here.


Take care and best wishes,
Robert

[opey456]

Went back yesterday afternoon checked all the duct work to make sure it was clean and all of it was even crossover pipe.Then unsweated the suction manifold from the evap. coil and blew back nitrogen through each cap tube and each one blew through fine. Replaced manifold evacuated system weighed in the charge and started the system. the pressures were 46 and 230 . The inside Temp was 77 degrees and outside was 65 . the suction line started freezing after about 15 min. of operation. the superheat was 16 . But had dropped to 5 by the time we turned it off. The coil fins are fine on the coil . The spec. plate on furnace only shows the unit should g to a 4ton but they have a 5 is there enough duct work for this application. ..i have had a couple of other opinions even had a guy who has done this for like 20 years and he was not sure....but something is causing liquid to get back to the compressor.........................

[Robert]

Hi,

Ok, let me look all this over and study it some. I'm at disadvantage from here, but I have 28+ years in HVAC service, so may can think of something.


Thanks for info.


Do you have the model number of a-coil ?


Take care and best wishes,
Robert

[Robert]

Just caught tonnage issue and that is definately a problem, may not be all or may be. Manufactured housing ducts are smaller than conventional homes and those specs are max on sizes advised.


4 ton is max size suggested without a duct modification on a MH.

To get anything for 5 tons for a MH, it has to be special ordered from factory and is not stocked for this very reason.


What is size of home ?


Has this went on since unit was new or did it ever work fine with 5 tons installed and if so, for how long ?


Can you do a ACCA Manual J Load Calc to see what size is really needed ?



Thanks,
Robert

[Robert]

What is brand and model number of the blower motor, can you get me that ?


Also, what is total condensing unit amp draw ?


What is subcooling ?


Discharge temp (use insulated temp probe-sensor) six inches from compressor ?


Thanks,
Robert

[opey456]

The MH is roughly 2100 SF. .The blower motor is a 3/4 HP 1075 RPM . But i the blower wheel size is 10 in DIA. and 8 inches wide. I looked on your site and it said for an electric furnace it should be 12x8 but that was for electric heat .But that should be the same size for gas furnace because it is the cooling we are worried about correct........ I did not go today will have to get discharge temp and subcooling when i go back

[opey456]

Also forgot to write the model number of the A Coil down when i had it pulled but i do remember it being a 60,000 BTU coil.


The MH is a 99 model. the first compressor lasted 7 years but the owner said it never really cooled great.

[Robert]

Be sure to get total condensing amp draw too.

Get the a-coil model number off it next time over there.

I believe the 5 ton issue is going to play a big part in this.


Thanks,
Robert

[Robert]

Just wanted to add that a 4 ton unit, condenser and a-coil, with a 1/2 hp blower motor is maximum size for that furnace and ductwork.


I would start there. If they wish to keep current system, a ductwork modification is in order.



Thanks,
Robert