Air Conditioning Gurus Needed

[bigvic]

I was hoping that some of you savvy AC guys could help me out with an issue I am having with my AC. It is not in my shop, but the AC for my house.

It is actually a conventional heat pump and has worked flawlessly since we bought the house last August. However, since we started hitting triple digits last week, it seems as though it has a hard time keeping up with the house, and when it is over 100 outside, it can't get below 80 inside. It will run all day trying to get there. So the first thing I did was call the home warranty company that came with our house and they sent some unheard of company out to diagnose the problem. After about 5 minutes of looking at the outside compressor only, he said that the unit was undersized for the house. It is a 3.5 ton unit and the house is approx 1750 sf. He also said that the suction line was 3/4" when it should be 7/8". In addition, he said that he hooked up the gauges and that the readings were where they were supposed to be. So basically I got to pay a $50 deductible for 5 minutes of inspection. He never did check out the air handler.

Regardless, I have a feeling that there is something else wrong that he isn't seeing. That deductible is good for 30 days so I have a little bit of time to figure it out without having to pay it again. So if any of you have any suggestions or recomendations on stuff to check out or what not, I am open to anything, and does what he said make sense? One thing that I do want to check out is the return air/treated air temp gradient. When the house was inspected the inspector mentioned that the temp difference wasn't quite where it needed to be, but he never said what range it should be.

Anyway, that is enough rambling for now, and I will appreciate any responses I get. One thing I do want to mention is that in an attempt to lessen the ac load, I installed an attic fan which has dramatically cooled the attic down and helped with the cooling problem, but I feel as though that is a band-aid repair and not a permanent solution.

 

[Luckydevil]

I just recently had a really good AC guy come out and he didn't charge me a penny for his inspection. Turned out to be some sort of faulty electronic switch on the air handler that was causing the same problem you are describing.

 

[Dave Carney]

Is your outside unit nice and clean? or are the fins clogged with dirt and debris? If it's dirty, spray it with a garden hose to clean it.

Do you have 4" exterior walls or 6"? How about the windows, Low E or no? 3.5 is small if it's not a well insulated structure.

 

[randydupree]

check the evaporator coils,they get bad nasty.get some coil cleaner,wash it down good,that always helps,i do mine every year.sometimes you need to remove a panel,and a good wet/dry vac helps out too.
randy

 

[bigvic]

Dave,

the ext walls are 4" and the windows are low E (albeit they are of the low end variety). The attic insulation is decent it could probably use a bit more, but we are only staying in this house for less than a year, and then we are moving into my new shop until our new house is built. That being said I don't want to put more money into this house, but I do want to make sure my AC is running as well as it can.

Randy,

Are you talking about the A-coil that is inside the air handler? I cleaned the coils on the compressor outside pretty good, but I haven't messed with the A-coil. It could probably use a cleaning. I will definitely check it out. You said you use coil cleaner. Is that something specifically made for this task that you get at an AC parts place or will a generic degreaser/cleaner do just as good?

One more thing that I want to throw out there. About a week or two before I noticed this problem, the capicitor went out on the compressor. I switched this out myself with an equivalent one that the AC supply house gave me. Is it possible that it is defective and is the underlying root of my problem, or not performing at 100%?

Thanks for your help so far guys.

Victor

 

[randydupree]

yes,the A coil is what needs to be cleaned. i buy the cleaner at johnstone supply,but i'm sure that baker bros,and the big box stores will have it too.
randy

 

[Three Stooges Racing]

I'm new here but am a HVAC guy by trade. If the outdoor temps and pressures are in line check the indoor temp drop. This is the difference in air temp at the return(where your filter is) compared to the temp at the regesters. Your looking for 14-20 degree diff. if its less than 14 your charge is not correct if its more than 20 you have air flow problems. At your "A" coil make sure you look at the side that gets the air from the return,thats where the restrictions will be. 3.5 tons should cool your 1700sq ft easily. Also try turning up your fan speed at the air handler, look at the wireing diagram,usually on the inside of the door and it should be easy to do. Just make sure you turn off the power first.
Good Luck.

 

[Bradley Miller]

Correct me if I'm wrong -- but I think the capacitor you replaced is just the start capacitor . . . it shouldn't affect the running. Right?

 

[bigvic]

Thanks TSR, I will look into those things.

Correct me if I'm wrong -- but I think the capacitor you replaced is just the start capacitor . . . it shouldn't affect the running. Right?

Yes, that is what I was assuming as well, but I just wanted to ask to make sure. Thanks.

 

[mrl05]

This is a great thread as I am experiencing the same problem with my heat pump.

I am in a brand new house (1yr in May) and my upstairs heat pump will not effectively cool the upstairs on any sunny day with outside temps above 85*. I had technicians out last year right after the house was built telling me (mumbo jumbo) that you're only going to see a 15* to 20* difference from the heat pump to outside air (not the return air). I somewhat bought the mumbo jumbo because I didn't know any better and went with it. Since no one is usually home during the day it wouldn't matter much. However, after spending a few days at home, I have really realized that this really is not right. In speaking to many of my neighbors, they indicate how cool their upstairs are so, I know there is something wrong with my system.

After seeing this thread and some of the responses, I decided to check the difference in temperature between the return air and the registers. I am only getting a 10* temp difference between the return air and the air at the registers - at night. The difference is down to about 6* at times during the day in sunny conditions. This is far below the 14* to 20* difference that Three Stooges Racing has mentioned and explains why my home does not drop below 80* until about 9pm in the evening. My system will run all day and when I get home, the temps say 82* - at 7pm. I know to expect some drop in performance on the extreme hot days, but this is everyday performance on my system.

I just called the HVAC company to come out and perform the 1 year system check as part of their agreement with the homebuilder and they are coming this Thursday. Is there anything else I should check or be armed with (knowledge wise)? When I called for service and indicated that there is a problem, the first thing the rep says is that on extremely hot days the upstairs heat pump system won't always cool as well. That's fine - I can deal with that on extreme heat days. Can you then explain why I can't get my house to 75* on a normal 85* day. Is that considered extreme too? She has no answer.

Let's say, the HVAC company tries to deny any problems and I have to get this repaired or replaced myself. What kind of costs would I be looking at? Is any of this diy for a homeowner? How is the "charge" fixed that Three Stooges Racing mentions?

Any help would be appreciated.

Thanks,
Mike

 

[Dave Carney]

Yeah, something aint' right mike. I have a 11 year old 4 ton goodman heat pump cooling 1874 sq ft ranch with full basement. When it's 108 outside, it can hold 75-77 degrees inside, though it runs all afternoon. What size is your upstairs unit and what's the square footage it's trying to cool?

 

[mrl05]

Dave,

Your scenario is similar to some of my neighbors. Many of them say they hardly run the furnace unit since the upstairs cools so well. Not the case for me though.

I don't know the size of the unit, but the square footage is about 1500. It has to be something in the compressor. Today, I came home to a 4* difference at 6:30pm - 85* room temp and 81* at the registers. At 9:30pm, the room temp is 81* while the air temp at the register is 72* - only a 9* difference.