ReplyThe unit has been charged at least three times with present air flow. Still the basic question - cools well with proper pressures,heat mode with optimal air flow pressures 610 high side? How come?
Professional Member*
Then it's likely overcharged, just as beenthere said.Originally Posted by THPRE
You can't say airflow is "optimal" until it has been correctly measured. Judging by your prior posts, we don't yet have an accurate assessment of airflow. You have to assure correct airflow on a heat pump or its a nightmare of problems, as you are seeing firsthand. This can't be measured by intuition or hope. Only by correctly obtained data.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Regular Guest
The unit has been charged at least three times with present air flow. Still the basic question - cools well with proper pressures,heat mode with optimal air flow pressures 610 high side? How come?
Professional Member*
This is a variable speed blower. How are static pressure readings going to tell us the air flow for certain anyway?
The "check me" diagnostic test was developed to verify that the correct speed settings were chosen by the installer for the variable speed motor.
The test is also supposed to verify that the charge level is correct.
Did your installer use the summer or winter protocol for the "check me" diagnostic test?
I've personally done many check me tests. I've learned that the summer protocol is useless for heat pumps. The problem is that the summer protocol forces the technician to charge to a specific subcooling value. This is guaranteed to produce an over charged heat pump in the heating mode especially on goodman equipment. The factory target subcooling value is just to high.
The winter protocol for the check me diagnostic test should be used.
The technician should be installing the flow plate for the test in the air handler or duct work. It sounds as though he's putting the plate in the filter grille?
I suspect that the blower speed selection is to low and the check me test may not be accurate.
Professional Member*
It has been charged three times with nobody verifying if airflow was correct or not. You need to realize that with heat pumps, there is more "slop factor" on the cooling side than the heating side regarding airflow. Not that this is a good thing. It just allows subpar techs to get by until the compressor dies. If none of the techs who charged this system while it was in cooling mode paid any attention to superheat or subcooling readings, they were not in a good position to catch refrigeration cycle problems. If airflow is not good on this system, which seems evident, then it will indicate such in both heating and cooling modes when measuring the refrigeration cycle.
As for why your head pressure at the moment keeps swinging back and forth, the compressor could be internally bypassing. It won't live much longer if that is the case.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Regular Guest
I think I can say optimal in that we are talking about reducing head pressure, not overall system function or performance. This test was done at the request of the Goodman representitive. I was watching the gauges when the ducts were disconnected under the house thus providing increased [optimal] air flow. I have no way of knowing what the changes were to the static pressure or the cfm with the ducts open and the filter removed but the pressures did not change. And after all the static measurements were taken with the system operational except that the filter was removed. Air flow static pressure was measured at .3 total . with fan at 144 cfm was 2140 , with fan at 88 cfm is 1647. I'm told you expect approx. 400 cfm per ton is that correct? How does a heat pump manage the difference in refergerant needs from cooling [large condenser] to heating with a smaller condenser?
Regular Guest
The compressor is hitting the high pressure switch not bypassing, unless bypassing turns the compressor and fan off. Off at 610 and back on at 400 in under 1min. From cold start up it takes about ten min to get to this point -- then it stays there! Yes I do worry about the longevity of the compressor--do scroll compressors have reed plates? Can they vary the speed of the compressor to change pressures?
God Speed, Jim. We'll miss you - 2-26-23
Charged incorrectly the same way 3 times, is still an incorrect charge.
Professional Member*
It looks as though the evap coil is turned 90 degrees from its intended position. The top of the blower might be restricting the outlet of the coil. That would definitely explain the low static pressures. That TXV installation looks like hell. Sorry.
Professional Member*
You could take all the ducts off, but if the charge hasn't been changed, it can still indicate as overcharged.
A heat pump outdoor coil is sized to reject heat from the indoor coil, refrigerant superheat, heat of compression, and compressor motor heat when the system is in cooling mode. In other words, it can reject more heat than the indoor coil can pick up, in most cases. In heating mode, this margin of extra capacity is very small. The indoor coil can quickly run out of room, as far as ability to dump heat, if any one or more of the following factors are out of whack: Airflow, refrigerant charge, lineset size and length.
Psychrometrics: the very foundation of HVAC. A comfort troubleshooter's best friend.
Regular Guest
Most logical answer so far!! Yes check me was during the summer. Protocol he used?? Reading the report - True flow plate measured air flow1403;charge test med
Professional Member*
I think those numbers (144 88) are actually pressures in pascals and refer to a cross reference chart when the flow plate is used to verify air flow. Unfortunately my cross reference chart is at the shop. I'd hope he's using the value for the 20x20 flow plate and not the 14x20 plate.
Anyway if the airflow really is that high then it was probably charged in the cooling mode every time.
If that's the case, have the technician charge the system using the winter protocol. He probably added (and documented) 2-3 lbs of refrigerant as per the summer protocol. He can remove that amount and then adjust as per the winer protocol. Since the system utilizes an indoor txv it will adjust for the conditions.
Again this assumes That your airflow is correct.
Regular Guest
Yeah--it looked better before the first time he replaced the tx valve . I told you early on he is a friend - not a the best tech. But he is a hard worker and is not charging me for all these service calls. This is why I have had another company out here doing the check me and duct work. They are well regarded in this area for their expertise. I guess I have no idea if the evap coil is oriented correctly or if it restricts the air flow. Pictures have been sent to Goodman they should know.
Professional Member*
Make sure you Read my last post.
Our target airflow should be 1600. With your low static readings it should be easy to achieve the 1600 CFM that's recommended. Assuming that the blower isn't on it's highest speed already. The blower default is 2000 CFM so it likely has been adjusted down.
I'm still Leary of that coil position.
God Speed, Jim. We'll miss you - 2-26-23
That would be low air flow for a 4 ton.
Regular Guest
Everything you say sounds correct as to the measurements. The system has been charged at least twice for winter and then will not cool in summer without adding refergerant. This system has been charged so many times I have lost rack - but is always the same result - take it out for winter and add it back for summer.
Regular Guest
What would you expect?
Professional Member*
That's a classic airflow problem. The 4860 evap coil should be the right coil.
Professional Member*
1600 as per post 73. 1400 CFM is allowed to pass the check me test. The test allows for airflow as low as 330 CFM per ton.
God Speed, Jim. We'll miss you - 2-26-23
1600 CFM to 1800.
Professional Member*
Like I said the top of the squirrel cage housing might be restricting the outlet of the coil.
The fact that the coil door is 3 inches away from a wall is the kind of stuff that drives a technician crazy. A little instant karma for the installer who had to change the txv though!
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