Why is my house so difficult to cool? HVAC suggestions needed!

[Tully_Mars]

@the raindog

That is an expansion valve and it located at the evaporator inlet. It can be replaced without replacing any of the coils, or system. It’s about $300 to replace.

Thanks for the info. I going to replace the whole system anyway with a 19 SEER unit. This one is 10 years old and it has been one nagging problem after another for the last 5-6 years. I figure the electricity savings may not pay for the new one for many years, but reducing the monthly cash flow is something I want to do anyway. I just need to fit the replacement into the schedule and budget. I also want to reinsulate the flex duct into the master bedroom with something that will stay on.

[raindog]

@Tully Mars

Thanks for the info. I going to replace the whole system anyway with a 19 SEER unit. This one is 10 years old and it has been one nagging problem after another for the last 5-6 years. I figure the electricity savings may not pay for the new one for many years, but reducing the monthly cash flow is something I want to do anyway. I just need to fit the replacement into the schedule and budget. I also want to reinsulate the flex duct into the master bedroom with something that will stay on.

Most of the flex duct made in the past has been R-4. In Ohio, code now requires R-8. The new R-8 flex we’ve bought and installled has been very good stuff. Bigger and a little harder to use (especially in tight spaces) but good stuff. Certainly doable as a DIY project. (and affordable!)

[raindog]

@the raindog

There has been some good suggestions, (and I think many would help) but the problem is in the A/C system.

First things first:
You mentioned a “basis for comparison.” Here’s some:

1. Houses of your age will require one ton of cooling per 500-1000’ ft². The most common would be 700 sf² per ton. At 700 ft² per ton, your house should be around 2800 ft². (given that you told that you us have a 4 ton unit; 4x700= 2800) The better the windows, insulation, attic ventilation etc the more you can get. A well constructed house may get up to 1000 ft² per ton. A poorly constructed house as low as 500ft² per ton. Note Ca3799 has a 3 ton system serving 2100 ft²

What is your square footage [of living space served by this unit] ?

2. I agree with Dag Otto that 65° is high. However we don’t know if that is a problem without knowing what the humidity and temperature of the house was when the tech read 65°. A correctly sized, and correctly installed and serviced unit will produce a 20° drop accross the coil. If the return air temperature was 85° then 65° was OK; particularly if the house was humid. So we [you] don’t know if the 65° is/was a problem unless we know/knew what the return ait temperature is/was, and the humidity. When the house is comfortable, the A/C system will produce a 20° drop from your “cold air return” to your supply registers. A typical reading would be 75° return air, 55° supply air, at 50% relative humidity. If you go out of town and turn the A/C system off, you will come home to high humidity and high temperatures. You may have 95° return air and 75° supply air; a 20° drop! But…as the house “recirculates” the air, the return air and supply air will both move down in lockstep. Make sense? So, take a thermometer and tell us:

What is the return air temperature, supply air temperature and relative humidity?

Other questions that will help us tell you what to look for:

1. Brand of A/C? Model number?
2. Programmable thermostat? Do you use it?
3. Does this house sit on a slab? Is there ductwork in the attic?
4. Do you run the fan continuously?
5. Where is the thermostat located?
6. What size furnace? (Btus)(and blower if you know it)
7. Does this unit have a history of refrigerant leaks? Does it use R-22? (or 410A?)
8. Is there ductwork in an attic? Is it insulated? Has it been inspected?

If you really want to get anal and find the problem call the service tech back and ask him to check out the system. Set the thermostat for 75° several hours before he arrives.

Ask him to record the following information, before and after. (Before being defined as before he makes any adjustments whatsoever)

1. Static pressure test of condenser. This is a little uncommon but it will tell if there is air in the system. This will require: A) PSIg reading of condenser/system with system turned off. B) Accurate reading of outside air temperature at the time pressure was taken. (We’re looking for something called the “P/T relationship” of that refrigerant)
2. Outside air temperature and humidity.
3. Inside air temperature and humidity.
4. Return air temperature at return air register.
5. Return air temperature at the point of entering furnace.
   (The reading between item 4 and 5 should be no more than 1-2°. If #5 is higher it indicates that you are picking up heat through the return air ductwork; a sure sign of leaking or broken ductwork in an attic sucking in hot air.)
6. Supply air temperature.
7. Fan speed setting
8. Suction pressure and head pressure
9. Both superheat and subcooling
10. Identify the type of metering device

Note that this information is not extraordinary. A professional tech harvests this information every single day. (with the exception of item one, that takes 90 seconds to perform) The point is, this is a garden variety service call and is part of a routine preventive maintenance call. It shouldn’t cost you any more than a basic PM call—$89 or so in my parts.

Anways…You haven’t given us enough information to diagnose this. However…my guess is that there is a problem with the A/C system. All of the other ideas are good—including your own. However they are not addressing the “root cause” of the problem. If you do this-----and I strongly suggest you spring for the $89***-----remember, before and after.

(*** look at your utility bill if you’re struggling with that)

Edit item #6
6a) Temperature of supply air just above evaporator coil
6b) Temperature of supply air at supply register

Your supply duct is under positive pressure so it will not suck in hot air like the return duct will. Still, there shouldn’t be more of a 1-2 degree rise between 6a and 6b. If there is, it is not a sign of broken/leaking ductwork but poor insulation; the Btus from a hot attic are infiltrating the duct and you’re picking up heat in the duct. (As Dag Otto noted. This could be the way to determine if you’re picking up heat in the supply duct)

[psiekier]

@the raindog

There has been some good suggestions, (and I think many would help) but the problem is in the A/C system.

I’m sure there are a lot of factors; this is probably the biggest.

However, I discovered the other day that I don’t actually have an attic vent.

I went upstairs to perform a cursory examination of the ductwork to see if there were any obvious, gaping holes. There were none visible. I saw from the front of the house the position of the large vent on the brick veneer, just below the peak of the roof. I went back up to the attic to see if any of our attic stuff was blocking a the vent, and realized that there is a sheetrock panel in front of where the vent should be!

There’s obviously space behind the vent in the veneer – that much I can see from the ground level – but how this thing is supposed to work with a slab of sheetrock right behind it has me scratching my head!

@the raindog

First things first:
You mentioned a “basis for comparison.” Here’s some:

1. Houses of your age will require one ton of cooling per 500-1000’ ft². The most common would be 700 sf² per ton. At 700 ft² per ton, your house should be around 2800 ft². (given that you told that you us have a 4 ton unit; 4x700= 2800) The better the windows, insulation, attic ventilation etc the more you can get. A well constructed house may get up to 1000 ft² per ton. A poorly constructed house as low as 500ft² per ton. Note Ca3799 has a 3 ton system serving 2100 ft²

What is your square footage [of living space served by this unit] ?

1,969 square feet.

@the raindog

2. I agree with Dag Otto that 65° is high. However we don’t know if that is a problem without knowing what the humidity and temperature of the house was when the tech read 65°. A correctly sized, and correctly installed and serviced unit will produce a 20° drop accross the coil. If the return air temperature was 85° then 65° was OK; particularly if the house was humid. So we [you] don’t know if the 65° is/was a problem unless we know/knew what the return ait temperature is/was, and the humidity. When the house is comfortable, the A/C system will produce a 20° drop from your “cold air return” to your supply registers. A typical reading would be 75° return air, 55° supply air, at 50% relative humidity. If you go out of town and turn the A/C system off, you will come home to high humidity and high temperatures. You may have 95° return air and 75° supply air; a 20° drop! But…as the house “recirculates” the air, the return air and supply air will both move down in lockstep. Make sense? So, take a thermometer and tell us:

What is the return air temperature, supply air temperature and relative humidity?

I need to get my hands on a thermometer accurate enough to test this. Maybe it’s time for a trip to Fry’s or Home Depot.

@the raindog

Other questions that will help us tell you what to look for:

1. Brand of A/C? Model number?

I’m not sure. I’d have to go back out there and look at it.

@the raindog

2. Programmable thermostat? Do you use it?

Yes, and yes. We keep it warmer in the day (warmer still when we’re not home), and cool off around bed time when the outside air is already cooler.

@the raindog

3. Does this house sit on a slab? Is there ductwork in the attic?

Yes, and yes. The ducts in the attic are flexible and wrapped in some kind of silver padding that doubtlessly contains insulation inside. It looks to me like the padding may actually be part of the ducts.

@the raindog

4. Do you run the fan continuously?

No. The fan only runs when the cooling (or heating - they are both connected together) unit is on.

@the raindog

5. Where is the thermostat located?

Both the thermostat and air return are located in the center of the house just beyond the laundry room that functions as an airlock to the garage. There are four air conditioning vents (laundry room, front bathroom, two kids’ rooms) within about a 12 foot radius.

@the raindog

6. What size furnace? (Btus)(and blower if you know it)

I was up there the other day, but didn’t take notice.

@the raindog

7. Does this unit have a history of refrigerant leaks? Does it use R-22? (or 410A?)

We’ve never had a refrigerant leak. I’m not sure what kind it uses.

@the raindog

8. Is there ductwork in an attic? Is it insulated? Has it been inspected?

Yes, Yes, and only once - just before we moved in.

@the raindog

If you really want to get anal and find the problem call the service tech back and ask him to check out the system. Set the thermostat for 75° several hours before he arrives.

If I do, I think I will pick a different company other than the one that the home warranty company sent.