Gas and Oil Home Heating Furnaces - A/C runs too long

My A/C unit runs from sun up to sun down and will not cool the house lower than 75 degs when the temp outside is 80 deg or higher.This started after I had a new furnace installed.I had the contractor check it twice and he said there is nothing wrong.I had another contractor ckeck the a/c and he said the charge is good and the system seems to be functioning properly. Prior to the install, my a/c worked great and cycled normally.The air coming out of the registers is cool(about 60degs) but not cold.I am certified in auto a/c and know i have a problem. Any suggestions would be greatly appreciated. I have an oil fired updraft furnace and a 2 1/2 ton a/c unit. Filter and returns are clean.

At 1st thought maybe the blower wasn't on high speed but a 74 degree supply air temp with the A/C running! Be sure the furnace is not running with the A/C.Something is not right. Also are these real HVAC contractors? Ask around and get a reputable company to look at it, you've got a problem.

SorryMattison register temp is 60 degs. checked and fan is set in the high position heat definatley not running ...thanks for the reply

Sounds like maybe you're not moving enough air. You said the filter is clean and the return too. If air flow was restricted you pressures would be off. What I would check next is to be sure they installed at least a 3ton blower "1200cfm" at least.

Didn't think to ask but when you had the furnace replaced did you also have the A/C replaced ?

Can you post the; Make, Model, & Serial numbers...

The unit is a Heil model#NUOD084BFA1
OUN084B12A1
Serial# C982656446
and no none of the a/c components were replaced.
Thank you again for your time!

Dear hd88--

Got just a few questions to help us eliminate possible causes of your problem:

Is it the both the indoor fan and the outdoor fan running all day or just the indoor fan running all the time?

What temperature is your thermostat set at?

Are you sure the thermostat fan switch is not set to the 'on' position when running the system in cooling?

How long has it been since the furnace was changed out?

Have you checked for ductwork which could have been damaged when the furnace was changed out?

Do you know what the brand and model of the old furnace was?

Both outside and inside fans run(so is the compressor)
the thermostat is set at 74 degs
the ductwork looks good
the thermostat fan switch is set on "auto"
the new furnace was insalled 2 yrs ago andhad this problem every summer since.It is the same make and model as the old one.I dont know if the blower was swapped out with the old one.

New Heil furnaces of your size are normally capable of handling airflow for up to 3 tons of a/c. Just out of curiousity, how old was the old furnace that was replaced?

13yrs old

Have you checked the indoor a/c tubing for kinks and do you know if you have an expansion valve or capillary tubes at the indoor coil?

indoor tubing looks good
has cap tubes

By the model and serial I saw it looks to be made in 98' and should have a 3 ton blower. I would call pro in and not let them go until problem is found. Have them confirm it's a 3 ton blower in the airhandler.

Did you change the thermostat when install the new furnance? Could it be that you had a two-stage thermostat before and used a single-stage one for the new furnance that does not turn on the high speed of the AC compressor.

One thought just occurred to me. I had a similar problem on an a/c system I serviced. The problem there was that when someone installed the evap coil, they failed to block all other airflow off around the coil. Consequently, a fair amount of air would bypass the coil (path of least resistance). The pressures were good on the a/c but all the air was not forced to pass through the coil. If your evap coil was removed and reinstalled, maybe they did the same thing. If the coil is in a cabinet you can forget that idea but if it is mounted in the plenum, check it out.

Ken

Thanks for the replys i will check those things out

double check pressures,what is you temp. split sup.&ret.,physically check return duct for any disconnection,if t-stat replaced check to see if hole in wall not big enough to influence temp. reading(sensing of inside temp).