[jax1]

What; a 6 Ton unit? What are U talking about?

My mistake. I meant 3 ton unit. Good you caught that.

 

[garyed]

What size are those 4 runs?. For a 3 ton I would expect 9" runs.

 

[Shophound]

Lack of good transition aside, system may be slightly undercharged, resulting in evaporator coil being warmer in some spots than others. Either that or the coil is not being fed refrigerant equally.

I've also measured air moving through a duct that was thermally stratified. This was on a hot deck/cold deck air handler, where the two air streams are supposed to mix well before going to the various zones (multi-zone). Before we improved the mixing at the discharge plenum, we had some zones on the same duct run warmer than others. After the improvement, at most one degree difference between zones.

 

[jax1]

What size are those 4 runs?. For a 3 ton I would expect 9" runs.

Correct

 

[jax1]

I did notice that this white 1/2 inch PVC pipe on the side of the coil plenum is blowing air. I assume this is an emergency water drain, but is it normal to blow air unrestricted?

View attachment 275741

 

[garyed]

Correct

That rules out over sized ducts causing the cold air to take the first path out because of not enough resistance. I would put a temperature probe at different points in that short trunk line. Maybe the top half of the trunk is warmer than the bottom half & the air is escaping through the first two take offs before it has a chance to mix evenly. Maybe some air is bypassing the coil or like was suggested the charge is not right & the whole coil is not completely cold.

 

[jax1]

... Maybe the top half of the trunk is warmer than the bottom half & the air is escaping through the first two take offs before it has a chance to mix evenly...

That could be. I did not drill holes into the duct junction box, but this is a mild day, attic is 78, and I measured the box's exterior. The top is 75, the bottom is 68 for a difference of 7 degrees. Today the register temp difference is 7 degrees (61 for the far ducts and 54 for the near ducts). Could be a coincidence, but if not, what would it take to fix it?

Also, 68 seems like a lot of temp loss from the box bottom. Does the junction box need more insulation?

 

[garyed]

It really sounds like you've gone as far as you can go without having a tech to come out & check the refrigerant level & go over the system for the solution to your problem. Either heat is being added to those two ducts or some of the cool air is not getting to them. Hopefully it will be obvious once the system is checked by a technician.

 

[jax1]

It really sounds like you've gone as far as you can go without having a tech to come out & check the refrigerant level & go over the system for the solution to your problem. Either heat is being added to those two ducts or some of the cool air is not getting to them. Hopefully it will be obvious once the system is checked by a technician.

Will do. My goal was to decide whether to call an HVAC tech or duct sealing company. I will start with the HVAC tech. Thanks for helping me be a more knowledgeable customer.