JAV I belive what I am going to say has been hinted at but not talked about in depth. I also believe the calcs that were originaly run were most likely correct except for the fact they should have run the heat loads, upper and lower, seperatly and not together. What this would have done is to give the downstairs part of the house no ceiling heat load and therefore lower cooling requirment downstairs. That would have required a different alocation of cooling than you have now which is 2 1/2 tons upstairs and 2 1/2 tons downstairs making the upstairs unit carry some of the downstairs load. This is often the problem with two story houses especially when there are rooms downstairs that have high ceilings that go into the upstairs space as you said you have. I won't go into if or not your systems are running properly. You said that this has been a problem from the begining so it all boils down to this: if your mechanical units were running properly on start up and continued to do so into your first cooling season the problem lies in the fact that your system designers never condidered the fact (or did not want to address it) that your cooling requirement up and downstairs were different (and they are) and how they would deal with this difference and still maintain comfortable air flows. The reason I say comfortable air flows is because to increase cooling they would have had to increase air flow (or volume or cfm). What needs to be done without having to change unit sizes is to give some of the upstairs heat load to the downstairs unit. One way to do this is to connect another return air duct to the downstairs air handler and install the other end of this duct or the pickup end as high as possible in the upstairs space such as the upstairs hall ceiling or a high wall. The location must be open to the major portion of the house. Not in an area that is closed off such as in a bedroom. This duct should be large, sizing is very important, also the farther it has to go the larger in diameter it has to be. If you did somthing like this you would have to keep the fan setting for the downstairs unit to the on position all the time during the cooling season to be very effective, also at the connection of the new additional return air on the downstairs unit you should install a damper so that you could partially,not compleatly, block off the existing old return during cooling and force the air handler to pull from the new return, during the heating season so as not to disturb the air movement during winter because winter heating is good the way it is move the damper so as to close the new return. An important thing about a damper set up to do this is that you never want the damper set up in such a way that if it loosens from its setting that it would starve the air handler of return air. Installing a return like this esentially destratifies the house so to speak. I hope I have made myself clear and helpful. Regards bd
sorry for the long hiatis. I was away on vacation and didn't have computer access. (I've also been lazy while enjoying the mild weather.)
Here is an update for those that remember. We finally had some warm weather last week (1 day) and I was going to compile some data on how the system was performing. I turned the upstairs system on the day before temps were projected to get into the 80's. The system did run at some point that day (we were out) but it held temp (set point 76 but outside temp only got to 78). The following day we hit 86 and the upstairs was 82 with the same 76 deg. set point. I went out to the compressor to check things and found the fan running but from the sound I could tell the compressor was not. Both high and low side lines were at ambient temp and no condensate was flowing. I double checked the t-stat and relays and found the compressor should have been running. I shut down the system thinking I might have a tripped thermal and tried again after about 1/2 hour. The compressor tries to start but sounds bound with some mechanical friction noises. It (the compressor) trips off after several seconds and only the fan runs. Its clear that there is some amperage load as the fan on the neigboring condenser seamed to slow while the compressor was trying to start.
I guess this could explain the fluctautions on the low side previously detected.
At this point, I will be replacing the condenser but I want to get a good pro in here to re-evaluate things and make some recommendations. I've had very bad luck in this department & tried as previously posted to go on the NATE website but found no certified companies in my area. The yellow pages also lists no NATE or RYSE certified companies. I'm going to try the local HVAC supply house to see if they have any recommendation on a sharp tech.
I have a few last questions that I'm hoping someone can comment on. Keeping in mind that the second floor system never worked well since new I think it's fair to be concerned with just replacing a bad condensor and not considering that other problems may exist. I'd like some feedback on what some techs have previously suggested... installing a 3 ton condensing unit and leaving the 2.5 evap coil (as thats the largest that will fit in the hydro-air handler in the attic). Is this done and what are the drawbacks? Also, since Laars doesn't support cooling any longer, what equipment choices should I avoid? I know Goodman is frowned on by some but their scrolls seem to be liked by others.
Thanks for all the help.
It's possible that, if your compressor on the ailing unit doesn't have a crankcase heater, it is struggling to start due to liquid refrigerant that has condensed in the crankcase. Apparently from what you've said the outdoor temperatures where you are have have been cool until now. Since you've been away and not running the unit this might explain what sounds like a hard start condition.
Or you're locked up and your compressor is DOA.
If that's the case I would be persuaded to seriously rethink your upstairs cooling configuration. You've never been satisifed with what's there and just plopping in a new condenser of the same size will likely not help anything. There are other companies out there that make air handlers that have hydronic and evaporator coils combined in one package. First Company comes to mind, among others. Other posts have mentioned ductwork problems, if I recall correctly. Now seems the time to get every flaw of your old system eliminated and start anew with a well designed system that will give you the performance you're after.
I would ABSOLUTEY go for a 3 ton unit if you need to change yours. I would still look for a great contractor and install a TXV valve in your unit for a more consistent superheat on your evaporator coil.
Also i would seriously look at adding some of the upstairs load to the downstairs unit and Absolutely look hard at the operation of both systems.
Adding upstairs load to the downstairs system makes alot of sense and I wish there were a resaonable way to accomplish this in my house. But, this would not be an easy modification. The great rooms second story center wall does not line up with the 1st floor center wall because of a cantilevered balcony. Also, the fire blocking in the walls would need to be removed.
As far as the 3 ton condenser, I agree that going 3 ton given the inadequate cooling makes sense but my question is related to the mismatch between the 3 ton condenser and the 2.5 ton evap. coil. I know enough to know that I'm a babe in the woods here and this theory is too involved to just make changes without considering the consequences. I know there are experts here that can explain the pros and cons of this approach.
Does your house have knee walls upstairs? Have you had your duct system pressure checked with a duct blaster?
Sorry if this information is irrelevant but since it's such a long thread I only read the first and last page. Here are my two cent worth.
If you had a 10 degree split at the upstairs unit you had some cooling going on but system was not operating at capacity. Something is definitly wrong with your system.
xavieryz made a good point about thermal siphoning. I have seen this quite often with zone systems that use circ pumps with no zone valves or check valves. You may be heating and cooling at the same time. A simple way to check this is to feel the hot water lines going to the air handler. If the are hot the you have thermal siphoning. thermal siphoning is caused by the convection of the hot water. the hot water will rise and the cooler water will drop causing circulation through the coil. this is very common with air handler located above the boiler.
The operating pressures you described sounds like non-condensables in the system. If your compressor has not been damaged you might remove the charge, evacuate and charge the system. the compressor might still be good if it is cycling on the internal thermal overload because of high superheat.
thanks for the replys,
to answer your questions, yes I have some knee walls upstairs. But, code in my area requires solid fire blocking at all levels and long floor spans. So adding ducting from the basement to the upper level of the walls in the second floor would be quite involved.
No, I've never had the ducts pressure tested. Is that done? Could you describe it?
No, don't have any thermal cycling... it was discussed in page 2 or 3.. sorry this thing is so long..I think I'm goin to start a new post as I just had another bad experience with a local pro.
The reason I asked those questions is that IF your system is operating properly, these two items could be the culprits. first the kneewalls--Kneewalls leak a lot of air. Fiberglass insulation does not stop air, only conductive heat gain/loss. This is very hard to calculate in the original heat gain/loss analysis. You may have 2 or 3 times the infiltration rate for this part of the house that was calculted for the whole house.
Second and most important, ducts can lose as much as 30% of cooling capacity by leaking. Not only that, but they can set up pressure imbalances upstairs to greatly INCREASE the already high air infiltration rate from the kneewalls.
A duct blaster is a calibrated fan that pressurizes the duct system and can tell you how much and where the leaks are. Call your local utility and see if they know a contractor that does this. Also could check for energy raters in your state.
There's 5 pages of replies here. if you heard this, forget about it... I have seen the problem before. Is the return duct adequate? It should be slightly bigger than the supply registers to allow for "equal" pressure (and allow easier return flow).