20+ years york ac compressor replacement

[JoJoMix]

Hello everyone,

This is my first post in this forum and I hope the issue i'm about to present is simple. First of all i'm not an AC professional but I have moderate background and experience with AC as DIY. I live in United Arab Emirates and there are no real professional ac technicians so that is why I wanted to present my issue here.

My uncle house have central AC system installed for more than 20+ years, YORK brand. Each is around 7 tons and one of them recently got a bad compressor.
https://s31.postimg.org/o62vtybyj/20160312_155114.jpg
https://s32.postimg.org/e4s5w59h1/image.jpg

I brought an AC technician who suggested replacing the compressor after several attempt to make it run but failed. The compressor is 3phase copeland BRE4-0750-TFD-501 with LRA 91.1A
https://s31.postimg.org/fxhnnd2yx/20160312_154601.jpg
https://s31.postimg.org/4mjlcqlhn/20160312_161246.jpg

Unfortunately this compressor is not available anymore and I asked many shops around and they suggested a piston compressor brand bristol with LRA around 72.

Bristol compressor is wider but shorter and the piping were little different so technician had to work it out to install the compressor properly.
https://s31.postimg.org/6jim65tzf/20160602_135317.jpg
https://s31.postimg.org/yxo1q1hjf/IMG_20160623_WA0000.jpg

The system was flushed properly with r141b and old filter drier was removed and replaced with new one after flushing was done. New compressor installed and system was vacuumed for like 4 hours and there were no leaks. Then gas charged r22 to around 60 psi on suction side to test cooling.

https://s31.postimg.org/gfjp5szrf/20160531_224942.jpg

cooling was fine but not close to the other systems with copeland compressors. Also readings of pressure from other system were taken to make sure the new compressor replaced system is under same conditions. I know that following super-heat is better and would do after finding the problem.

The indoor duct temperature was around 16C ~60F and the compressor is running normally and warm to touch. However the suction line going to compressor should be usually cold but in this case it is around 27C ~80F

Another system with copeland compressor has suction line around 8C ~ 46F and this picture for the system. Ignore icing as it was due to low gas charge and adding little gas solved it and reading was taken to be 8C.

https://s31.postimg.org/bu7xkdzt7/20160619_151310.jpg

So my problem is that there is not enough cooling and the compressor bristol is a bit smaller than the old copeland one but the temp are way far and cooling is really weak. I thought maybe there was a restriction in system. Technician found out after a week that the filter drier was installed opposite side so he opened it and installed it correctly thinking this was a restriction. He charged gas again and let the system run and got same result.

Hope you could suggest me as I did call other technician and they could not find the problem and suggested changing the compressor. I will post picture of the piping line and evaporator/condenser if needed but the system is well built quality and coils are great and have no leaks.

Thank you very much :)

[Recoilzn]

How sure are you that you have the right replacement compressor?

[chemi-cool]

The copeland is 7.5 HP and the bristol is 6 HP.
Bristol makes 7 or 8 HP.
You should check the copeland scroll compressors.

[JoJoMix]

How sure are you that you have the right replacement compressor?

Hi Recoilzn

I am sure this is not the correct compressor and it seems smaller. That what was available and many shops suggested this one. True it is smaller maybe by 20% but could the cooling really go down like that? I mean original copeland compressor for a system next to this one has suction line temp around 46F and this bristol system has suction at 80F. I read that suction pressure should be higher and not to try make it 60psi like other systems and would follow super heat.

[JoJoMix]

The copeland is 7.5 HP and the bristol is 6 HP.
Bristol makes 7 or 8 HP.
You should check the copeland scroll compressors.

Hi Chemi,

You are right about bristol that they have these 7-8hp, but they were not available and that is what I was suggested to install. Will get more info like head pressure and temp around filter drier to remove guessing. Thanks :)

[chemi-cool]

One more point, your system is either overcharged or there is air restriction.
Suction pipe should not be frozen, check the air flow or superheat.

[JoJoMix]

One more point, your system is either overcharged or there is air restriction.
Suction pipe should not be frozen, check the air flow or superheat.

Hi Chemi,

that picture with fronzen suction line is for another working ac system just took it to compare. The technician checked that frozen suction and pressure was around 42psi, undercharged. He charged to 60psi knowing that there is leak just to get correct read and all ice gone and got suction temp around 46F. The damaged system has bristol compressor installed and technician tried to get same condition of suction pressure 60psi to check compressor operation that is all. So it is not cooling and I still didn't have time to go again get more data.

Sorry for the confusion :)

[Recoilzn]

Hi Recoilzn

I am sure this is not the correct compressor and it seems smaller. That what was available and many shops suggested this one. True it is smaller maybe by 20% but could the cooling really go down like that? I mean original copeland compressor for a system next to this one has suction line temp around 46F and this bristol system has suction at 80F. I read that suction pressure should be higher and not to try make it 60psi like other systems and would follow super heat.

You should be charging via superheat. That compressor is about 20000btu's smaller, original copeland had a 97100btu capacity, the bristol has 75000btu, which means it will take longer to reach temperature and the compressor will battle under high heat load. In short the compressor is probably inefficient to the task. Whats the room temp and ambient temp, compressor running amps?

[JoJoMix]

You should be charging via superheat. That compressor is about 20000btu's smaller, original copeland had a 97100btu capacity, the bristol has 75000btu, which means it will take longer to reach temperature and the compressor will battle under high heat load. In short the compressor is probably inefficient to the task. Whats the room temp and ambient temp, compressor running amps?

Hi Recoilzn,

I will check the system again and call the technician to charge according to superheat, to be honest I didn't see any technician charge using this method but only fixed pressure and suction temp. The room temperature is around 75-80F and ambient outdoor around 104F midday and 80-85F at night.

This 60psi pressure was done during midday. I will check the drawn amp and head pressure and note it as soon as possible. Really grateful for your help :)

[Recoilzn]

You right they normally weigh it in, but in this case the name plate looks unreadable as to the amount of charge required. Hope this helps.
http://http://www.achrnews.com/articles/84939-charging-air-conditioners-with-the-superheat-method

[kefah]

Hi all
as i live in Iraq so we have same extreme hot weather
replacing compressor with smaller one
surely will lower efficient
also he must charged it to 70 or even 80 psi
because 60 psi will not be enough in very hot temperature

in temperature as 30s 60 psi is enough
but in 40s or 50s higher pressure must done so cooling will be ok

[JoJoMix]

Hello everyone,

Sorry for the absence as the owner of house was on vacation and I was able to get the data few days ago. I took the points suggested to me and took different measurements hope it helps.

The system was purged first till suction pressure went to 40psig and data was taken. Then every 15min waiting the system was charged with refrigerant r22. The table shows all the values.

https://s32.postimg.org/zdu72a5et/chart.jpg

Outdoor condenser Fan leaving air @120F
Outdoor drybulb temp @95F
Indoor wetbulb @70F

I was also measuring the temp accross the filter drier (inlet and outlet) and it was the same so no restriction. I also searched for data sheet for both compressor (old one copeland BRE4-0750-TFD-501 and new one bristol H2BG094DBEE) and found that copeland is around 95600 btu/hr and second is 88700 btu/hr so almost same cooling capacity.

I even called the company that provided the bristol compressor and said that their data sheet says both compressor are the same and around 2000 btu difference.

Now the last measurement I took was at 90-95 psi suction pressure and around 300psi head pressure. Values seems high but at these pressure the suction line started condensing water and was cold to touch (@70F) which i guess is good. indoor duct temperature was around 66F and I was hoping to get lower 60 and below.

Last, the refrigerant gas used was brand refron R22 which is top brand used here and all HVAC companies use it. Does a refrigerant gas R22 differ in cooling capacity from brand to brand given that they are same chemical structure (R22) pure to 99.9%?

I am worried to leave the compressor at these pressures although it was working cool and not even hot after 2 hours operating.

Thank you very much

https://s31.postimg.org/v03jf9ve3/20160711_172722.jpg

[JoJoMix]

Hi all
as i live in Iraq so we have same extreme hot weather
replacing compressor with smaller one
surely will lower efficient
also he must charged it to 70 or even 80 psi
because 60 psi will not be enough in very hot temperature

in temperature as 30s 60 psi is enough
but in 40s or 50s higher pressure must done so cooling will be ok

Hi Kefah,

Yes you are right regarding hot weather and increased system pressure. I took new data hope it helps.

[JoJoMix]

Hi Recoilzn,

Name plate is too old. Maybe I will work out a method to clean it and color in the engraving to get better detail :)

[kefah]

i measured many brand ac unit system suction pressure
during very high temperature
suction was between 70 to 90 psi
suction line cold
i think your system is ok
best wishes

[JoJoMix]

Just quick update today

I checked the AC one more time to see if the compressor is heating after letting it work for 2 days. Everything was fine and compressor was cold to touch. Suction pressure was around 87PSIG and suction temperature was 70F

I charged more ***** and observed the suction temperature. It dropped to 64F when i reached almost 90 PSIG.
https://s32.postimg.org/mqvuipp5x/20160714_180752.jpg
https://s32.postimg.org/4dfq8eobp/20160714_184640.jpg

I wait for 20min and then charged gas again, the suction temperature kept dropping but the suction pressure was staying the same at 90psig and was able to get lowest 57F on suction side.
https://s32.postimg.org/qo3l8dllx/20160714_184540.jpg
I stopped there as I didn't want to charge more gas as the pressure was staying the same. The condenser air was around 121F
https://s32.postimg.org/uj6zay4rp/20160714_183603.jpg

Indoor air coming from duct was around 68F so is that normal or should be cooler? suction temperature at compressor is 57F.

[JoJoMix]

i measured many brand ac unit system suction pressure
during very high temperature
suction was between 70 to 90 psi
suction line cold
i think your system is ok
best wishes

thanks mate :)

[r.bartlett]

are you still trying to make an undersized compressor work like the correct one. My view is if the compressor is cold you have reached the point of overcharge (assuming everything else is correct) and maximum performance. by adding gas you don't make it better.

[JoJoMix]

are you still trying to make an undersized compressor work like the correct one. My view is if the compressor is cold you have reached the point of overcharge (assuming everything else is correct) and maximum performance. by adding gas you don't make it better.

Hi Bartlett,

I only tried more tests because the shop and online data showed that the new compressor has the same specification as the old one and difference in btu/hr is around 2000-5000 which is negligible. I did charge gas slowly and stop for 15min to check check the suction pressure, indoor duct temp to reach the lowest point while keeping high side in safe pressures. I also cleaned indoor filter and evaporator coil completely with pressurized water.

[Gary]

Indoor air coming from duct was around 68F so is that normal or should be cooler? suction temperature at compressor is 57F.

The air temperature leaving the indoor coil should be about 20F/11K lower than the temperature at the thermostat in order to get ~50% RH. You will need to slow the indoor fan to achieve this. With the current setting it appears that you will have high indoor humidity.

Once the fan speed is adjusted, you will probably need to remove some refrigerant to get the right suction line superheat.

[JoJoMix]

The air temperature leaving the indoor coil should be about 20F/11K lower than the temperature at the thermostat in order to get ~50% RH. You will need to slow the indoor fan to achieve this. With the current setting it appears that you will have high indoor humidity.

Once the fan speed is adjusted, you will probably need to remove some refrigerant to get the right suction line superheat.

Hello Gary,

You are right about the air leaving indoor coil should be cold. Whenever I measure indoor coil air in split ac or duct it is usually 50F and below. For this system it is around 20 celcius/ 68F which is warm to be honest.

I have to provide more pictures about the indoor system and the ducting. the system is covering 2 rooms and small area of big hall, thermostat set on 15C/60F and compressor is always working nonstop. The fan speed in duct is slow as I checked and not fast.

[Gary]

The new compressor is undersized for the evaporator. Slowing the fan speed reduces the evaporator capacity to match the compressor capacity, bringing the system back into balance.

The air temperature leaving the coil needs to be 20F/11K cooler than the actual current temperature at the thermostat (not the setting). It is the difference between these two temperatures that is important.

[Gary]

If you take a volume of hot humid air and cool it to 50F/10C, it will shed just enough water to give you 50% RH if you then raise its temperature to 70F/21C. That's why air conditioners are designed for a 20F/11K drop across their evaporator coil (20F/11K delta-T or dT).

[Gary]

https://s32.postimg.org/zdu72a5et/chart.jpg

Outdoor condenser Fan leaving air @120F
Outdoor drybulb temp @95F
Indoor wetbulb @70F


The saturated condensing temp (SCT) should be 20F-35F above the outdoor drybulb temp (20F-35F TD). With 95F outdoor temp, the SCT should be 115F-130F (pressure 245psi-300psi for R22).

#4 is overcharged (40F TD).

30F TD would be a good ballpark charge (125F/275psi for R22 at 95F ambient).

The suction line temp is high because the compressor is undersized for the evaporator, which can be remedied by slowing the fan speed. This will drop the suction line temp. Its all about the balance.