Possible HVAC Problem

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Nezil

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I purchased my current home almost exactly a year ago. Come to think of it, it really was actually a year ago exactly today!

During the initial purchase phase, I had the HVAC system checked because I felt having lived here for two and a half years (I purchased the rental property that I'd been living in from the landlord) that the system wasn't cooling efficiently enough.

The guy that came out to check the system initially claimed that the fan in the furnace had failed, then the capacitor that was on the fan, and in the end claimed that the furnace control panel needed replacing. At one point he put the fan back in the furnace and shorted something out that caused the capacitor that he'd replaced to get really hot... I pulled everything out after he'd left, fixed the short and put the original capacitor back in and the system has been working fine, at least as good as it ever has, ever since... The guy clearly didn't know what he was doing!

At the time, the previous owner did offer to pay for the control panel to be replaced ($1,000), but I said that a) there is nothing wrong with the control panel, and b) if that guy is going to be doing the work, I don't want him anywhere near the system.

Fast forward a year, and I decided to take another look at things, and maybe consider replacing or upgrading the cooling components.

I've looked up the details of the units; the compressor - Nordyne model FS3BA-030KA; and the coil, Nordyne model C3BA-036C-A. Initially I thought that these were a correctly matched pair, but this document: http://www.nortekhvac.com/Literature/a949a.pdf, states that the required orifice size for the 030 outdoor unit is 0.063, and the label on my coil says that it has an orifice of 0.067 - the size required for the 036KA 3.0ton outdoor unit.

I'm pretty handy, and after taking advice from others on this forum fitted my water softener, including sweating of 1-3/4 fittings from the main water line as it comes into my house. HVAC is completely new to me however, and I'm not sure how much of this can be tackled myself.

I'm particularly worried about calling someone out and paying for a consultation that may be as misguided as the guy that came during my purchase. At the very least, I'd like to know what I'm talking about so that I know whether to trust whoever comes out.

So I'm looking for advice, ideally some tests and checks that I could do myself by taking covers off the coil etc and taking measurements, to see if this oversized orifice is indeed the problem. It would be nice if I could just change to the correct size orifice, or upgrade the outdoor unit to a 3ton one to match, and then see my system efficiency improve dramatically.

Thanks in advance for the help!

Neil.
 

Jadnashua

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It's illegal to vent refrigerant into the atmosphere, and to open up the cooling system, you have to remove it. This is normally done with a vacuum pump and the coolant is recovered. IOW, the average person won't have the tools to work on an a/c unit except maybe to add some refrigerant (you'd want at least a good set of gauges). Unfortunately, this is usually the job for a professional. Some things, like replacing an electrical component can be done along with cleaning the coils, etc., but opening up the lines takes specialized equipment. Depending on the refrigerant, some of the older ones are VERY expensive, if you can find them at all. Modern a/c units are required to be (often, anyways) a LOT more efficient than the older ones. Depending on your electrical costs and the age of the existing unit, a replacement may be warranted. This usually means both the evaporator coils in the air handler/furnace and the compressor unit.
 

Stuff

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What the label says is that the coil came with the bigger orifice installed from the factory. When the system is installed the tech is supposed to take the orifice that comes with the condenser and use that one instead. That's not to say some idiots don't just throw it out.

How do you know what your efficiency is now? What is the problem you are experiencing?
 

Nezil

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Thanks for the comments so far...

I did realise that actually filling (and emptying) the system was likely to require some outside help, but was hoping mostly to diagnose the system myself so that I could be confident that what a professional was offering was a) going to address the issues that I was having, and b) wasn't simply skewed to coax me into spending un-necessary money.

It's unfortunate I know, but the contractor who visited me previously has left me with no confidence that I'll be able to find an HVAC contractor that I trust - I'm happy to hear suggestions for contractors here as well if that's not against the forum rules; I'm in northern California by the way - South bay area.

Regarding the problem that I'm facing... it's pretty much that the system struggles to get the house down to the temperatures that I'm setting, and the compressor is cycling on and off all day long. Maybe I'm wrong, but I'd expect the system to bring the house down to the set point in a couple of hours, and then cycle on for maybe 10 minutes per hour after that. As it is today, it does produce cool air, and it does reduce the temperature of the house, but it's just very slow at doing so. I'd have thought this was a sign of an undersized, or underperforming system.

I realise that this is very vague details, but my home is approximately 1,700 sqft, 3 floors in a sort of town house style - It has only one shared wall that is insulated from our neighbour. The compressor is a 2.5t unit I believe, and it was built in 2003.
 

WorthFlorida

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When the system blows cool and not enough cold air, usually it is low on refrigerant and there is no leak, just low; Are the coils freezing up? Installed in 2003 it most likely is a R22 refrigerant and no more than a SEER 13 but maybe a SEER 12. SEER 10 were outlawed by then. Today, the minimum is SEER 14 0r 15 for efficiency. R22 by 2020 will no longer be allowed to be sold in the USA. It is best to replace the entire A/C system. There are quieter and more efficient. A three floor unit you have the heat load might be overwhelming the system therefore it cannot keep up with the cooling.

I just replaced my 3 ton unit after getting an A coil leak. the system was only installed in 2007 but the coil replacement cost was more than half the cost to replace the entire system. I replaced it with a SEER 15 Carrier unit and got a $395 credit rebate on my electric bill. Two months before the break down I had all of the up stair windows tinted. A big difference the way the home stays cool and the A/C runs less.
 

Nezil

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That's interesting, though I don't think PG&E is offering credits on A/C or window tinting...

The unit that I have is SEER 10, and is also R22 refrigerant, the labels on the outdoor unit state as such. It is therefore inefficient, even if it is working correctly.

I have a feeling that I might just be overloading the unit. My home has no shade on two sides, the third faces the other homes in our complex with a driveway between, and the forth is the joining wall. The two sides that have no shade are East and South facing, which is pretty bad, though at least the heat load is slackening off slightly in the afternoon.

I will have to have a look and see if the coils are freezing up. This is the sort of question that I was hoping to be asked. What does that mean if they are?

Do you mind saying the ball-park figure that you paid for your 3ton replacement system? Looking online at coils and outdoor units, it looks like I'd be in for at least ~$500 for the coil, and $1,000 ~ 2,000 for the outdoor unit. I'm guessing perhaps another $1,000 for installation?
 

WorthFlorida

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Icing on the coils mean restricted air flow such as a dirty filter or low on refrigerant. Low refrigerant pressure lowers the boiling point and the coils will have a temperature below 32 degrees therefore condensation freezes.
For my three ton unit with a heat pump model installed was north of 5k. A/C only unit might be 500-800 less but you are in CA. This is not a DIY project. You must use an ac guy that is certified so you'll need to pay the big bucks. With two homes I've had to replace a few units and it takes two tech's about five hours to do with all the right tools ; vacuum pump, gauges, duct work, etc.
 

Nezil

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I realise that this is not a DIY thing, though I was hoping to be able to at least diagnose the issues...

The information that you've given me is very valuable. I should be able to take some temperature readings of the coils and see if they're freezing up. Thanks very much for the advice!
 

Dana

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Ducts that are undersized for the air handler and restricting the total air volume can have similar symptoms. Air-sealing undersized ducts will often aggravate coil-icing issues. Upsizing the coil to match the compressor won't fix air flow problems, and if the ducts are indeed undersized, improving the ducts is more likely get you to the sought after capacity & efficiency problems.

What type of ducts, how tight are they, and are they located in an attic above the attic insulation, or ... ?

Get a box-store pistol-grip infra-red thermometer (about $50 for the cheapest decent versions) and with the system running go measure the exit air temps at all of the supply registers, and the temperature at the supply plenum of the air handler.

If the system is working-mostly and not leaking refrigerant it's often cheaper (and always better) to reduce the load by upgrading the thermal envelope of the house with improved air-sealing & insulation, or adding exterior shading for the PM solar gain windows to get the peak load down rather than replacing the system. Air sealing the house AND the ducts is important for reducing air-handler driven air infiltration but if the ducts are undersized it may make the icing issues worse. Prioritizing the air sealing of ducts and air handlers that are outside the pressure boundary of the house should have priority over air sealing of ducts that are fully inside. Both supply & returns need to be air-sealed.

Pay attention to any non-ducted return paths. A doored-off room with a supply duct but no dedicated return will need jump duct or a door cut or similar to create an adequate return path, otherwise flow is restricted, and the room becomes pressurized relative to the outdoor air pressure, and any leaks in the walls/windows/ceilings/floors of that room makes the "great outdoors" part of the return path.

IIRC, under CA Title 24 2013 (which went into effect a month ago) when you replace the HVAC equipment it requires that the equipment not be oversized by more than 10 % 0r 15% (don't remember which) from the calculated load via Manual-J methods, and the ducts have to meet air-tightness of no more than 6% of the air-handlers rated flow, and the ducts need to be brought up to Manual-D for size & duct design. It's legal to repair non-compliant equipment without taking those measures, but if your place needs extensive modification to get there it could add up to quite a bit o' cash if it requires retrofitting an all new duct design that might mean breaking open walls, etc.

But even if it's an SEER 10 system that's 3x oversized for the actual load, if it can be made to cool the house by either fixing the house or fixing the unit, it will be much less expensive than outright replacement. Getting some quotes/proposals for replacement systems could put that into perspective.
 

Tom Sawyer

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Any hvac tech with a thermometer and a set of gauges can tell what's going on in about fifteen minutes.
 

Dana

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Any hvac tech with a thermometer and a set of gauges can tell what's going on in about fifteen minutes.

That assumes a level of competence not in evidence, based on the experience with the last HVAC tech, and the potential mis-match of the original system (which was probably a different idiot.)

Nezil seems to be looking to self-educate before talking to the next idiot that comes out to assess the system, to make it easier for him to assess the competence of whoever walks in the door.

It's unlikely that a 2.5-ton coil in the air handler with a 3-ton compressor is undersized for the load of a 1700' townhouse, and it could easily be 2x oversized. But there could easily be comfort issues related to crummy duct design/implementation.

"Maybe I'm wrong, but I'd expect the system to bring the house down to the set point in a couple of hours, and then cycle on for maybe 10 minutes per hour after that."

Actually, that IS wrong! With a right-sized system if you let the house heat up to something north of 80F during the day on an 85F July day (85F is the approximate 1% outside design temp for the south bay area towns, but you can look yours in the Appendix 1B) and you come home from work at 5PM and expect it to get to 75F in two hours those expectations would not likely be met. A right-sized system would have to run 60-minutes out of every hour just to stay up with the load on a hot day during the peak hours, dropping to a lesser duty cycle later. Dropping back to 10 minutes/hr would only happen after the house is in full shade as the sun goes over the hill, and the air temperatures have moderated by quite a bit.

As an experiment, try a "set and forget" approach rather than turning it off while you're away- see what the ACTUAL duty-cycle is when you return home. A typical peak load of a 1700' house would be between 1 & 2 tons with peak occuring in the early to mid-afternoon. If you're arriving home in the later afternoon when there is still at least some sun on the house with air-temps still in the 80s it should still be more than a 50% duty-cycle if sized correctly, but it should be keeping up. If it's cycling only 1o-15 minutes an hour between 4-7PM on a day when it hits the mid-80s it's way oversized- oversized to the point that it's probably not operating quite at it's nameplate efficiency.

The peak grid load in the CA-ISO grid is typically ~8PM, and NOT during the air-conditioning peak load. That is an artifact of people leaving the AC off during the day, then coming home, cranking on the AC while they head for the showers (turning on the hot water heater) , cooking meals, & settling down to eat while spinning up a Bollywood chick-flick on the big-screen TV, etc. A good thing for reducing grid infrastructure costs would be to pre-cool the house during the day then turning off the AC between 6-10PM, since that would reduce the absolute peak grid load.

As more solar power goes onto the CA grid the evening peak load creates a ramping problem for the generators and grid operators, since the solar output is fading just as the evening load is starting to pick up. If/when rates get restructured to promote different use patterns it may become financially advantageous to pre-cool as a matter of course. The ramp problem is more exaggerated in the early spring when mid-day loading from AC is even lower:

Screenshot-2014-03-25-14.36.08.png


If you're billed at flat rate based on just energy usage it doesn't make pure financial sense to pre-cool, but you'd be more comfortable if you did.
 

Tom Sawyer

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Well, one bad experience doesn't mean that a competent tech isn't available. If you know how to interpret pressure and temperature readings and calculate super heat and sub cooling, then ductwork issues, and sizing issues all become instantly apparent from the numbers alone. While educating yourself is a good idea, the equipment and its proper use takes some experience to learn to do correctly.
 
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