Air Conditioning - Temp Differentials and Run Time

Unit is 4 ton Carrier, package unit in manufactured housing, about 8 yrs old. Ambient temperature when readings were taken was 86 at 8:00 PM. Humidity was 87%. Run time was 17 min and off time was 6 min. Water was steady from condensation pipe. Best duct register temp was 61 at middle of run. return air register temp was 72. I put an IR temp gun on the suction side near the compressor and temp was 84. High side was 197. (these are Farenheit temps, not gauge readings) Condenser temp was 116 with air flow. This morning, temp at registers was 65 and at return air was 74. Electric bill increased by 275 KW hours over same period from last year. No changes in living conditions. Question: Do the temp differentials sound about right or are they not enough. I was thinking they should be about 14 -16 degrees difference. Thanks for any replys.

Filter clean coil clean???? We like a 16o to 20o drop over the coil at the coil.

I put an IR temp gun on the suction side near the compressor and temp was 84. High side was 197.
Is this the copper line temp???? you want the little copper line warm and the big copper line cold and wet comeing from and going to the high side of the unit.

ED;)

Filter is new and coil was cleaned about a month ago. Copper suction side was 84 and high side was 197. No sweat on suction side when running. Suspect a very slow leak at this point. House is still comfortable at this point but a 275 KW increase in my power compared to last year got me started on checking the temps. Still under parts and labor warranty with Carrier. I called today and someone will be out Wednesday to get some gauges on it. Thanks for the reply.

Update: after two days with two different tech working on the unit we are nowhere. Owner of AC company now suspects a hole somewhere in return ductwork to unit (14"). Ductwork was installed new in 1998. This is under a manufactured home. I crawled under this morning and duct look good. I use IR thermometer all along duct and got only a 2 degree change on the outside of the ductwork. Return air at the register is about 74 and about 78 as it comes in to contact with the evaporater coil. It leaves the coil at 58 degrees. Temp at the supply register is about 64 degrees. Air flow seems real strong at registers and at return. (new filter). As I watched the techs work, I noticed that only the back side of the evaporator was sweating (copper lines that loop) and the front side was warm all the way down. There is also still no sweating on the suction line coming from the compressor anywhere. Remember this is a package heat pump A/C 4 ton Carrier unit, seer is 12 and unit was new in 1998. There was a recently (3 weeks ago) replace control board and the changeover valve. The symptoms on that occassion was no thermostat power at all. I am not convinced that there is a ductwork problem, I still think I have a compressor problem even though the techs say the pressures (68 suction and 275 high side ) are about right. They tried releasing and then adding some R22 but things got worse. The unit is under warranty (parts and labor) but the ductwork is not (even though it was installed at the same time by the same dealer that is working on it.) My cost for new duct work supply and return of about 35 feet is going to be 400-500 dollars. I would like to be sure before that work is done. Work is scheduled for tomorrow. Any opinions would be appreciated.

How many sq ft is your house ?

about 1430 under air and heat.

Return air at the register is about 74 and about 78 as it comes in to contact with the evaporater coil. It leaves the coil at 58 degrees. Thats a 20o drop over the coil. Id say the unit is working as good as any unit can.

I noticed that only the back side of the evaporator was sweating (copper lines that loop) and the front side was warm all the way down. There is also still no sweating on the suction line coming from the compressor

You say new in 1998. They tried releasing and then adding some R22 but things got worse. The unit is under warranty
8 years old.Gauges on and off . They could have contaminated the system with noncondensables
Just out of the box here.

ED;)

Thats a 20o drop over the coil. Id say the unit is working as good as any unit can.



You say new in 1998.
8 years old.Gauges on and off . They could have contaminated the system with noncondensables
Just out of the box here.

ED;)
If that's the case would you also suspect a leak in the return duct line?

A 4 ton unit in a 1430 sq ft home seems oversized which would give you short cycling, high humidity, and other problems. Has it always in the 8 years cycled like that ? 17 minutes on and 6 minutes off is bad.

No it has worked very well, I am on the east coast of Fl with high humidity and living in manufactured housing to boot. The unit also has three skylites and one east facing wall is all sliding glass doors with two more sliding glass doors leading to an enclosed screen room. Most all of the units where I live have the 4 ton units.

I just went outside and put the water hose on "mist" and directed it to the fan pulling air across the condensing coils. The supply register has now dropped to 59 degrees with the return air at 73 degrees. The low side of the compressor and the accumulator are now sweating. I turned the hose off and 10 minutes have passed with the same readings. Why the sudden change and how long should it last if the "mist" is not on the unit? This is becoming a brain teaser....thanks for all the replies.

I just went outside and put the water hose on "mist" and directed it to the fan pulling air across the condensing coils. The supply register has now dropped to 59 degrees with the return air at 73 degrees. The low side of the compressor and the accumulator are now sweating. I turned the hose off and 10 minutes have passed with the same readings. Why the sudden change and how long should it last if the "mist" is not on the unit? I have ran in to mist water on the condenser before. It has always been dirty coils inside and out with the unit way over charged.Thats like here the oak pollen alone in the condenser coil will make them go off on high head some times.

ED;)

Update Friday morning7:30 am: Unit ran well all night. Still seeing 14 degree differential from supply to return inside the house. Called dealer early this am and asked him to consider holding off on the new duct install. He got quite "testy" (as I probably would have...being hard headed myself) and insisted it was a duct problem. He basically told me that he was through fooling with it and me I guess. I told him that I was going to probe the return and supply during the heat of the day and see what wall going over the coil before I spent 500 dollars to redo the ductwork. He said it didn't matter because according to his tech I still had 80 degree air coming into the evaporator. I asked him where I could be getting 80 degree air since the air under the crawlspace was only 77 degrees. No response just aggravation with me I guess. Anyway, I guess I have compromised the relationship with my Carrier dealer now and will have to look elsewhere. I still have two years left on the warranty for the unit. The ductwork was also installed new 1998 by this same dealer when the new unit was installed. I may try to post some more accurate numbers this afternoon and see what you all think. Again, appreciate the replys.

Update: 7:00 pm Friday Night

Used temperature probe midday and got the following:

Probe into return air where filter is located: 70 degrees
Probe into ductwork at entrance to outside unit just before crossing coil: 70 degrees
Probe into ductwork at supply from outside unit just after leaving coil: 58
Probe into supply grill inside house: 59 (shortest run)62 (longest run)

I don't see how the ductwork could be leaking on the return side or the supply side. Unit is still sweating on the suction line from compressor and around the accumulator. Air feels ok inside but still not as good as in the past but much better than when I first called contractor for help. I guess I will have to try to find another company that is a Carrier dealer to take another look at it. Not sure what to do next on my own. Is there such a thing as a second opinion from another company without costing an arm and leg?

FWIW, you can buy your own ductwork, and it's fairly cheap. 30' would be less than $100.

I tend to agree that 4ton is way to big for that square footage, even accounting for the skylights and glass doors. At 1000 more square feet than you (and also in florida), I'm on a 4 ton with about 16 windows plus 3 glass doors.

That being said, a leak either in the return or supply sounds likely. Given the low temps in your crawl space, I'm leaning towards a supply side leak.

entrance to outside unit just before crossing coil: 70 degrees
Probe into ductwork at supply from outside unit just after leaving coil: 58

Thats only a 12o drop over the coil you should have about a 16 to 20 o drop over the coil.

ED;)

If I do have a supply leak, how does that explain the 12 degree drop over the coil?

More info: I gave the wrong sq. footage for the house. 1830 is what I should have posted not 1430. Apologize for that...

As I watched the techs work, I noticed that only the back side of the evaporator was sweating (copper lines that loop) and the front side was warm all the way down. There is also still no sweating on the suction line coming from the compressor anywhere.
I think you need to start looking at the coil being restricted.