Piping compressors in tandem is a frequent and common practice that works and has been successful for years. You have a major problem.....


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Should I have a 15 degree temp difference at the tee where they meet


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Which tee??


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The suction tee which is next to one of the air handlers. Each air handler is on a different floor of the building


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Are both air handler evap coils cooling at the same time? If there are liquid line solenoids controlling each evap then you should have compressor unloading. Also if you are unloading, piping design is very important. We have little knowledge of your system from what you posted but you possibly need double suction for oil return. You asked about a 15° td at a tee, what you should be asking your self is what is my superheat at each evap. What type of compressor failures have you had? Also Ryan1088, I think he has parallel evaps not tandem compressors.

 

No they do not cool at the same time and yes they do have liquid solenoids. My superheat at one of the air handlers is 20 degrees and I haven't got to check the other one due tithe lack of service ports. Now at the condenser my s.h. Is 35. But what I'm getting at is I think the piping is not ok. That's why I asked about the dt across it. The compressor that failed had a blown valve gasket and terminal lug gaskets. Also it got extremely hot as to melt some of the remaining gaskets. Now since start up of this compressor 2 days ago I have had to drain the oil twice because it has become to full of oil.


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Ok so does the compressor have unloaders? If only one evap is active then the compressor becomes over sized. 35° superheat at compressor is high. Check superheat with one evap at a time. If no unlading exists suction pressure will probably be abnormally low and superheat higher. As far as piping goes it's pretty hard to see what you are seeing without any description. Is the compressor above or below evaps. How far. Any traps and where. Double suction? This application should really have unloaders.

 

It does have a unloaded but I can not set it. My suction psi at the condenser is 40 psi with r22 and when it unloads my pressure drops so low that my suction sensor shuts the unit off. Now I've talked to Carlyle tech support and set the unloaded where they think it should be. And still same problem. There is an oil trap at the condenser and that is it. No other traps in the system


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The condenser is below the evaps and it is around 100 ft


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I believe you have 1) piping issues 2) unloader issues (loading at lower pressure and unloading at high pressure. 3) controlling issues. 4) you need to take some time explaining things here as several statement you have already made aren't making any sense. If you evap's are 100' above the condensing unit, your sub-cooling should be real high as 43# of pressure is lost in 100' of rise. I would suggest you obtain a Carrier piping manual and read it. We can't possibly under stand your piping design as you have given us nothing to use. Okay you have a tee combining the discharge piping and there is a 15*F difference in the line temperature of each compressor. Are both FULLY loaded when checking this temperature. Are these unloaders hydraulic (mushroom head or electric solenoids) ? Are they hot-gas by-pass heads or are they suction cut-off heads) ? -GEO

 

Well I've been doing hvac for 13 yrs and am new to this compressor and set up I've only worked on 1 other system like this on a complete new install and never could get it to work right. Even had a manufacturer tech look at it and he said it would never work right either. I know these systems exist and work right. If I gave u all the info on this system I would be typing for days so if you would ask the questions that you think are important to you I could answer them and we could all maybe learn something and solve my problem. I'm just lookin for help. It's a by pass unloader


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Rather than type for days, maybe you could draw it out for us? Obviously I mistook what you were talking about.


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Moved thread to Tech to tech discussion

 

I know that my unloader is not working at all. So should I have the right super heat at each evap. Right now one evap is at 8 degrees and the other is at 19 degrees of super heat. I'm thinking that the txv with 19 is bad but could the unloader effect that. These readings are with both units running. When one air handler shuts off my super heat on the one running goes to 30. Could both txv be bad or is this just because of the unloader


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One of the two A/H is not function properly. You have to find it yourself.
My guess is the TXV

 

When you say not working I assume you mean it won't unload. What should happen is when one evap is active the compressor should unload and provide a 60 to 70 psig suction press. when both evaps are active the compressor should load up. I would set my system to load at about 75 to 80 psig and unload at about 58 psig. As far as superheat one evap has hi sh. Check subcool at that one to insure you have liquid to the txv if you do you may need to adjust that txv, to lower sh. With the condensing unit below evaps no need for double suction but you still haven't given us any detail including line sizes. a drawing would be nice also. With unloaders not working properly I can see why the compressors failed but your people should have identified that long time ago. Until you get the unloader personally I would run both circuits together and never allow only one. That's what the unloader is for. The superheat is high with one circuit because the compressor is pumping more refrigerant than one txv can handle. The txv is full open but can't feed enough refrigerant because the compressor capacity is to high. I imagine you have a pretty pissed off customer and it sounds like your company are the wrong people for the job. No offense. You have to adjust your unloaders and watch the system. This is not simply as you put it "Just because of the unloader" IT IS BECAUSE OF THE UNLOADER!!! Ultimately you have to adjust it so it loads with two coils active an uload with one coil. I gave you start points but because of line lengths you have to make tis happen per your job. Carlyle can't give it to you either.

 

Do you have sight glasses at each liquid line before entering the evaps? Have you tried adjusting the TXV? Are there LL filter dries at the evaps? If so have you checked the temp difference across? Like others have said. Get some pictures.

 

No sight glass at either evap only at the condenser. LL filter is at the condenser along with suction filter. I have checked across both of them and the temp drop is minimal. My sub cooling at each evap is 33 to 40 degrees no matter which ah is on or off and my line temp is around 80 degrees


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My LL is 1/2" at the evaps and 7/8 before the tee. Suction is 1.1/8 at the evaps and 2" at the condenser . I did not try to adjust the txv due to the location of it. I would have to take apart almost the whole unit to get to it and I thought it was the unloader causing my problem. Pics are going to be nearly Impossible to get due to the location of everything. Ah are in closets and all the piping is is on the outside wall 4 stories above the ground. My company had two guys that took care of this customer and a few months ago they decided to start a company together. They serviced this system for years.

 

Carlyle 06E compressors are extremely sensitive to oil levels in the compressors. Too much oil will blow gaskets! Blown gaskets cause the compressor to run "burn the paint off" hot. Is this whats happening? Keep the oil level in the very bottom of the sight glass. Half a glass is TOO MUCH!

 

Is there an oil equalizing line between the two compressors? If not: With only one compressor is running it will pull the oil out of the other and store it in the compressor that is running. Then when the load increases and the second compressor fires up it has no oil in it, which we all know is not a good thing! If there is an equalizing line it should have a sight glass in it, when both compressors are running full load the oil level should be half way in the sight glass, when running one compressor unloaded it should be barely showing any oil in the bottom of the sight glass. This is due to the reduced velocity in the suction line which is why you will find oil traps in most split systems with tandem compressors. Either way, oil is the reason your compressors are failing.

 

I would just like to re-state that 1/2 a sight glass will cause compressor failure. Consult the green Carlyle service guide on page 12. It states 3/8's MAX and I'm telling you that based on my personal experience of remanufacturing compressors for 40 years that the compressor runs best with the oil level at the bottom of the glass.

 

I stand corrected on the 06E compressors, it does state in the manual that it is 3/8 Max, 06D's and smaller are 3/4 max in the sight glass.

 

This is a single 20 ton compressor with 2 10 ton a.h. But yes you are right about the oil 3/8 max. I've had to drain it twice due to old oil in the system when I did the change out.

 

Is your compressor a 4 cylinder or a 6 cylinder. Please post the model #

 

So lets get this straight.

You have one 20-ton condenser with a single compressor.
How many stages of unloading do you have?
You have two 10 ton air-handlers each with one coil and one TXV?
What is the model number of each unit.
What is the total foot of rise of pipe?
What is the total drop.
What is the net vertical lift.
What is the horizontal pipe length.
You indicated that you have 350 PSIG. Where did you take this reading? Are the coils clean.
What is your average suction pressure? 40 or 48 PSIG? Why are you maintaining such a low pressure.

35 to 40 degree sub-cooling? Have you verified that the refrigerant charge is correct.
What does the condenser name plate indicate for a refrigerant charge. Have you pulled the charge and weigh it back in. If so what is the total charge of refrigerant.

Have you installed new liquid and suction filter driers.
Have you opened the system at the TXV and verified that there are no obstructions. Are the screens clean.
What is your TXV superheat set point? and is it around 12 degrees? It sounds like you have an obstruction at the TXV or possibly a bad sensing bulb weak charge.

Have you figured out how to properly set the unloaders for the compressor. As a base point I recommend that you start to load at 68-69 PSIG and to start to unload at around 59 to 60 and be fully unloaded at no less than 58 PSIG. You do not want to be below freezing. This must be done first so that you can have a consistent system pressure.

If you have had previous failures what symptoms did you find. I have seen discharge valves and failed components downstream of the compressor a few times.

 

That unloading set up will cause short cycling.

Should unload around 58 psi and load up between 77 and 79 psi.