ReplyWas your compressor running loaded or unloaded?
Professional Member*
Found one of the fans not running on this one today. Found the fan cycle switch not making, so I opened the door to let the pressure rise, and it did finally come on. Put the door back on and the head pressure droped to around 205. The sight glass was full. The suction pressure was 60 and the suction line temp was around 68. The outdoor temp was 90 and the indoor temp was 76 per state regulations. Both fans were running with the numbers I am posting.
I hooked up and put in some R-22 to try to get the head pressure up and to get the line temp to around 90 degrees and the head to about 235. This is a TXV unit. It is a twin system, so the other unit is evidently toating the load. What bothers me here is that the suction line never got below 65 degrees the whole time I was charging it. The pressures seem to be dead on the chart numbers. I think that I know what may be wrong with this unit, but I would like to have your ideas to confirm my theory. I charged the other unit to pretty much the same numbers, but the line temp on it wound up to be around 45-50 degrees or so. Your ideas are appreciated here. Thanks
Professional Member*
Was your compressor running loaded or unloaded?
Professional Member*
I did not notice an unloader on the compressor. This compressor is smaller than the compressor on the twin unit. Being that neither of them seem to cycle, I would think that it would have been loaded. I must admit, I need to do some learning about unloaders. I see them a bunch, but I am not really familiar with what they do exactly. I do know that I usually see lower pressures when the unloader is engaged.
Professional Member*
That should be a 6 cylinder and should have 1 unloader whether it be enectric or pressure. If electric and it is energized then it is unloaded. De-energized compressor is loaded. Unloaded pressure suction higher discharge lower loaded suction pressure lowers and discharge rises. Can also check amp draw to check.
Professional Member*
I did not check the amp draw today, but I did look for the unloader. The part doesn't have a selonoid. It is basically a round piece at the bottom, goes into a larger round piece resembling the head of a TXV, and then goes back down to the smaller size of round at the top. The suction line was cool this morning, and the head was running around 190. This afternoon the line was back around 68 degrees.Originally Posted by thegoodlistener
The twin unit has a larger compressor, but they both are the same model unit. It also has an electric selenoid. I am wondering if Carrier made a change on this model. I did not see anything about an electric selenoid on the schematic of my problem unit.
While I am asking, what exactly powers up the selenoid to make it unload?
Professional Member*
There should be a normally closed relay in the unit and when y2 makes it causes the relay to open and takes power off of the unloader.
Professional Member
Hopefully this will be helpful; Carrier has two types of unloaders. The electric version has a small solenoid coil that energizes to unload and also enables the #2 condenser fan on some models.
The second type is a suction pressure controlled unloader that has a giant nut that unscrews to lower the suction/loading up the compressor. There is a small cap nut perpendicular to the setpoint nut that encloses the differential adjusting screw. Be careful not to run in hard the large sepoint nut or you will flex the poppet diaphragm and ruin the unloader.
Professional Member*
This must be the suction controled kind. I described it in an earlier post, but it comes out of the machine round, goes into a larger round part that rembles the head of a TXV(probably the diaphragm) and then goes into a smaller round piece. How do you know if the machine is running loaded or not with this type of unloader?
I checked today, and the suction line is still running around 70 degrees. I just can't figure out why the pressures look dead on, the subcooling is dead on, and the suction line temp is so high. Any help is appreciated.
Professional Member
The way to see if it is runing loaded/unloaded is by measuring the compressor-only amp draw. It will be closer to RLA when loaded. 99% of the time the problem you are looking at is due to one of the two TXVs on the coil having a flat powerhead or having too much spring pressure [valve adjusted too high of a superheat]. You might also have a closed liquid line solenoid on the second stage TXV also.
When you get the TXVs solved make sure your unloader setpoint is between 60-65 PSI and that the differential is >5 PSI to prevent hunting/wearing out the unloader. Only adjust the unloader setpoint nut by hand, do not use a wrench.
Regular Guest
This unloader is operated on pressure only. the suction pressure will drop if compressor is running at full capacity.get some literature from your carrier distibutor and it will show you how to adjust cut in and cut out of unloader.
Professional Member*
There is not liquid line selenoid, but if it was closed I would think that the suction pressure would go sky high in an effort to pump down the unit into the evap coil. Either way, the pressures should be off. I will try to adjust the TXV. I assume that when you say a flat power head, you are saying that the power head has gone bad? This is something that I wondered about, but I figured that the suction pressure would be really low because when a TXV goes bad, it closes down almost or all the way shut doesn't it? Thanks
Regular Guest
I was a little confused in your statement. If there is a liquid line solenoid and it closes the suction pressure will drop and the refrigerant will all go into the condenser not the evap coil.Sounds like you have a metering device problem.
Professional Member*
Don`t worry about the txv statement might be a little over your head right now but it will come in time.
Professional Member*
Sorry about that statement. I was thinking about it wrong. The liquid line selonoid closes so the liquid pumps into the condensor, which should raise the head pressure and lower the suction. This is not the problem. I have all good numbers except the suction line temp. I agree that it is probably a bad TXV. This was my original thought, but I was thinking too hard about the pressures being correct. I assume that this TXV doesn't shut down all of the way, which would cause a pump down type senario with the pressures.
I have not done much work with these larger TXV's that can be adjusted or the power heads changed out. I am wondering if someone can give me a briefing of how to adjust the TXV (I think that you take off the nut/cap on the bottom and turn the adjustment screw, but I don't know how much). I am also wondering if the power head can be changed out(if it is that type which should be evident by a nut at the bottom) without pumping down the unit. In other words, do the little rods that come through the valve body where the head screws off of the top leak freon by? Thanks guys!
Professional Member*
Probably not a bad txv just running unloaded. There are several systems out there that use multiple txv`s on one evaporator.to reduce capacity there is a liquidline solenoid to stop flow through one txv which lowers the suction pressure to onload the compressor to match the load of the active txv. I believe that was what Jax was referring to. But this will also happen when there is no load in the conditioned space.
Professional Member*
Ok, stick with me here and I will explain this system. They had 1 unit of the model @ that this post is named. That was not enough, so they added a second unit. So, in all reality, we have 4 stages of cooling on this one air handler when we take the unloader capabilities into account, which we should do by all rights. The machine that caries the first 2 stages is running right on the money. Now, there is a time lapse between when these machines were manufactured, and evidently Carrier made some big changes because the compressor is about 2/3 the size of the old machine, the unloader evidently is the type that works off of suction pressure, and there is no hot gas bypass line on the new model. I think that the hot gas bypass is for dehumidifying purposes, but that may be another post question.
So, I have 1 saying there is a metering device problem and another saying that the unit is running unloaded. If it is running unloaded, then it is probably overcharged now. I have a 98 degree day tomorrow, so I will check the line temp to see what it tells me. Otherwise, I am wondering how to load up this machine with the suction type unloader, if there is a way to do so. Any other recomendations will be appreciated as well.
So, what I am gathering here is that the TXV has not so much to do with the actual pressure on the low side, but just regulates the superheat. I thought that it had a little effect on both the pressure and the temp.
Professional Member*
First things first you need to find out if that compressor is running loaded or unloaded. Pressure seem ok to me I think if there was a bad txv suction pressure would be lower and discharge higher. When your compressor loads up this will happen. Do they have the same refrigerant circuits or are they seperated? Also verify the compressor model numbers on the compressor .
Professional Member*
Being that there is no selonoid to disengage in order to get this machine to unload, I do not know how to make it unload. Can you help me with this? As we have determined here, this works off of the suction pressure to unload. It should have been unloaded today if it ever will because it was 98 degrees here with high humidity.
Regular Guest
The piece you are describing on the compressor that is similar to a txv is your unloader, Carrier makes 2 types electric or manually adjusted.Yours is the manual type .Turning the large nut on top ccw will lower the pressure your compressor will load up[full capacity].
Regular Guest
If this machine is running unloaded, The coil would be frozen at this point, and you would have noticed that for sure. With a suction pressure in the 60's, we can all take for granted that the compressor is, in fact, loaded. If it was unloaded, the suction pressure would be higher. Even more evidence is the superheat. If the compressor is unloaded, and the txv were working correctly, and the refrigerant charge was ok, then the superheat would be 10-15 degrees. All of the information I have read on this thread is pointing me to the txv.
One thing I will ask though. With this being a multistage application, is the evaporator coil dedicated to this circuit, and this circuit only? In other words, the liquid line feeds either one or two txv's and the suction line for those circuits come back to only this unit? Answer that, and we can put this to bed.
If the evaporator is, in fact, dedicated, and has only one txv, then what you will need to do is adjust it. Take the bottom cap off, and while measuring the pressure, converted over to saturated temperature, also measure the suction line coming out of the evaporator. If the superheat is too high, which it is in this case, turn the port counterclockwise one turn and recheck, allowing a good 5 minutes to allow it to adjust. Usually one full turn equates to 3 degrees, but that all depends on the type of valve and manufacturer. Adjusting txv's are like turning on water hoses, clockwise will cut off the refrigerant, counter clockwise will open it up.
Posting Permissions