HVAC conundrum

[Mesozoic]

We're seeing ambient temps in the 110F range these days and if I set the thermostat to anything below 77F, the system is unable to cool any further. Would this be considered normal performance given the high ambients or should the system be able to cool right down to 70F or so?

I've got a 3306 sqft residence with high ceilings in several areas - and 2 central HVAC systems located on each side of the house. Each outdoor condenser unit is a 3-ton single stage model. One side of the house has been updated with a 14 SEER system, but the other side is still running the original system installed in 1996. Rheem Classic with a Criterion II furnace. The coil on the side with the original equipment is a 4-ton coil, so not sure what's going on there, but I'm basically trying to find excuses for my home warranty to replace my HVAC on that side.

 

[Jim greengo]

When was the last time it was serviced?
Is that sq footage all above ground,or are you counting the basement also?

 

[Mesozoic]

When was the last time it was serviced?
Is that sq footage all above ground,or are you counting the basement also?

It was actually just serviced yesterday, when the outdoor unit was relocated to a new location to clear the way for the garage. The sq footage is entirely above ground, there is no basement.

I recently had to replace the outdoor fan motor and capacitor - took care of that myself using a universal motor, but definitely got it working again. The compressor is a Copeland scroll unit, can't tell the age, but it looks good.

 

[samss]

The only way to know if the condenser coil is clean....is when you clean it. You'd be amazed at the dirt I've washed out of what LOOKS like a clean condenser. Is the small copper line (high side) hotter than the ambient temp?
Can you check your ductwork for obvious leaks? Is it in the attic?
The list goes on.

 

[Mesozoic]

I have thoroughly cleansed and flushed the condenser coil when I replaced the fan motor. It wasn't really bad, but I figured it was any easy thing to do once I had the fan and motor out, so I did it anyway. I've had the HVAC specialist go through the entire thing, so there's no leaks, etc. The air handler is located in its own mechanical room within the garage interior. I did touch the copper line coming out of the evap coil and again closer to the outdoor unit and it's certainly significantly hotter to touch than the ambient air.

 

[rharman]

We have a two story house and separate A/C for up & down. Upstairs will get to a point where it won't get any cooler - typically around 75 degrees if it's a really hot day.

I think a lot of it, in our case, is the house design. In the center where the stairs are, it essentially makes a big chimney for all the hot air to get trapped. We have a ceiling fan pushing it down and I usually have a small fan blowing up to help with circulation.

A well designed system can make a big difference. We lived with it a lot worse for years with the A/C installed when we remodeled (adding the 2nd story). Last year, we replaced everything including ducts and grills - same size system. Wow, what a difference!

Original ducting was a big end-to-end trunk with drops to each outlet. New ducting was sized to get progressively smaller as drops occurred - which is what I would expect.

 

[meathooker]

The ACCA guidelines show 75 degree indoor design temp. In Boise the ASHRAE outdoor design temp is 95 degrees. When it gets to 105 (which it regularly does) the system is doing it job if it the house is 85!!!! Contractors aren’t allowed to put more capacity in new construction homes.

It’s crazy that is what’s required and acceptable.

 

[LS6 Tommy]

It was actually just serviced yesterday, when the outdoor unit was relocated to a new location to clear the way for the garage.

Hey? Where did my post go?

I posted last week about this.

Was the unit cooling properly BEFORE it was relocated?

Tommy

 

[engineer2]

AC system cooling ability decreases as outdoor temperature goes up. The condenser just can't get rid of enough heat. Use your garden hose to spray a fine mist of water on the condenser coils while the system is running and see if it helps.

I've always heard if you buy a house in the hot parts of AZ make sure it's single story since you'll never be able to keep the upstairs cool in the summer.

 

[Mesozoic]

Hey? Where did my post go?

I posted last week about this.

Was the unit cooling properly BEFORE it was relocated?

Tommy

No, not really. The home inspection indicated that when we bought the house.

 

[Mesozoic]

AC system cooling ability decreases as outdoor temperature goes up. The condenser just can't get rid of enough heat. Use your garden hose to spray a fine mist of water on the condenser coils while the system is running and see if it helps.

I've always heard if you buy a house in the hat parts of AZ make sure it's single story since you'll never be able to keep the upstairs cool in the summer.

Yes, it is definitely not desirable to have a multi-storey home in southern Arizona, but modern HVAC with high SEER ratings seem to make it work, even when it's 115F outside. My current home is fortunately one level only.

 

[LS6 Tommy]

No, not really. The home inspection indicated that when we bought the house.

OK, at least that idea is out of the way.

Tommy

 

[Mesozoic]

OK, at least that idea is out of the way.

Tommy

I think a moderator has removed a bunch of posts because I posted quotes from my home inspection report - they are straight up missing from this thread now.

 

[Dagny]

The key to air conditioning a two story house is to **** the hot air out of the highest points in each room on the top floor.

 

[JoeMcGov]

It's all about: delta T. The difference in outside ambient temp and indoor temp that the system is designed to provide. If the systems design delta T is 25 degrees then when its 100 degrees outside you'll get a best of 75 inside.

Yes. There is a bunch of factors including the insulation R value of the various home elements.

So remember. If its 110 outside setting the thermostat to 65 isn't gonna make it any cooler inside.

 

[mrpizza]

Need to get a heat load performed on your house, then you will know if sized right. Duct sizing and air distribution is also vitally important.

My home is spray foamed well and the system is designed right and sized right. I can keep it 65 degrees even over 100 degrees outdoors if I want.

Edit: I put in a trane variable speed heat pump, makes a huge difference.

 

[Mesozoic]

I'm dealing with a 25 year old system that has been patched up and repaired over the years. it's definitely cooling, but it's not cooling very efficiently (electricity bills) and the lowest temperature it can achieve is currently 77F. That's with an outdoor ambient of around 100F, but it gets significantly hotter here in Tucson, Arizona than that. I'm considering upgrading the indoor coil and the outdoor unit with a matched combo replacement that will take it from R22 to R410 and add a few SEER at the same time. It's the most important unit in the house as it cools the kids' bedrooms, the kitchen, family room, dining room, and most of the areas that are occupied during day to day activity.

I used to have a 19 SEER dual stage Trane system in my old house and I really loved that system... very efficient.

 

[Terry D]

It's all about: delta T. The difference in outside ambient temp and indoor temp that the system is designed to provide. If the systems design delta T is 25 degrees then when its 100 degrees outside you'll get a best of 75 inside.

Yes. There is a bunch of factors including the insulation R value of the various home elements.

So remember. If its 110 outside setting the thermostat to 65 isn't gonna make it any cooler inside.

Delta T is the difference between supply and return air temp. Not outside and inside. These readings need to be taken right at the air handler or furnance. The rule of thumb is 18 to 22 degrees difference. Humidity inside, air flow and the correct charge will all have a factor in this. Some units these days could have a delta T as low as 15 degrees

 

[Mesozoic]

Our home inspection report stated that the delta T was 16F and called for a repair.

 

[engineer2]

There was a system crash last week and a bunch of posts disappeared.

 

[danski0224]

Our home inspection report stated that the delta T was 16F and called for a repair.

One would actually need to do a bunch of honest to goodness work and drag out some rather expensive test/measuring equipment to determine the actual operating capacity of the equipment, rather than condemn it based upon a rule of thumb measurement....

I's become much easier to do this today compared to even 5 years ago, but it is still well outside the scope of work of a "home inspector".

 

[rattle_snake]

35* in/out split seems about right. My home won't go below 75 with 110+ daytime heat load.

You live inside an oven. Suggest cold beer. If you have a pregnant wife, good luck.

 

[Git]

I'm dealing with a 25 year old system that has been patched up and repaired over the years. it's definitely cooling, but it's not cooling very efficiently (electricity bills) and the lowest temperature it can achieve is currently 77F. That's with an outdoor ambient of around 100F, but it gets significantly hotter here in Tucson, Arizona than that. I'm considering upgrading the indoor coil and the outdoor unit with a matched combo replacement that will take it from R22 to R410 and add a few SEER at the same time. It's the most important unit in the house as it cools the kids' bedrooms, the kitchen, family room, dining room, and most of the areas that are occupied during day to day activity.

I used to have a 19 SEER dual stage Trane system in my old house and I really loved that system... very efficient.

My 2nd floor unit had a complete failure back in May. The electrical connection at the condenser failed and all the freon escaped (I was there and heard it)

Opinions vary but is it really worth putting money into a unit that old that is still running R22? Ours was 17 years old and the simple answer was no. You probably can't even get an R22 replacement at this point.

So the next question - what do you do about the furnace side? Keep in mind if your just going to replace the AC side, your kind of limiting your self because both sides need to work together. We are in this house for the long run, so for me the best decision was a completely new, variable speed system. We even moved the outdoor unit, something we always had wanted to do, so it has a brand new line set, also. Best part - Home Warranty kicked in just over $8k, but it did take almost 2 months to get the check

How long do you plan on staying in that house and choose accordingly

 

[Mesozoic]

Excellent point about how long you plan to live in the house. We have also settled in our home and intend to reside there indefinitely. From the research I've gathered, there's 2 possible approaches for HVAC replacement on the side of our house with the old R22 system. The system is a Rheem Classic Criterion II.

1. There is a drop-in replacement evap coil kit with matching condenser that brings the system up to R410 and 14 to 16 SEER, reusing the existing air handler and furnace. Rough cost for this would be around $3000.
2. The other option is full blown system replacement, including the air handler and furnace. Cost varies depending on what system is selected.

I'm planning to wait for our garage construction to finish before doing anything with the HVAC at this point, but my plan is to engage my home warranty when I'm ready. I've already spoken to them and they did say that we're eligible for a full system replacement with no specified limits on cost. That being said, it's very likely that the warranty would only pay for an updated similarly spec'd system, so option #1 might the only one they'll pay for.

 

[Git]

With my warranty they paid $8,750 - $500 deductible for a replacement of equivalent quality.

No one wants to make these kind of decisions when your AC failed and it's getting to be hotter than hell outside, if you know what I mean. We ended up with a contractor through Costco and we were looking at around $10k for a full replacement (AC and Furnace) for a low end, single speed Lenox. We went with their top of the line unit (the variable speed XC25 with their matching furnace) for around $15k - but what really sold us on that one was how quiet the outdoor unit was and the energy efficiency (electricity in California is far from being cheap). I had just changed home insurance companies a couple of months ago and was mildly surprised when they came through on their 'appliance coverage' since the new insurance company was a lot cheaper.