Another AC won't cool below 80F Problem

[sskzekeman]

Fire this tech and get a competent one.
Should not have changed existing piston size. And should have taken airflow measurements and temps across the indoor coil.
Could be dirty coils in the indoor unit since a drop of only 10 degrees indicates quite a reduction in cooling .

[Kevin O'Neill]

Superheat of 5

According to my Goodman/Janitrol charging chart, with an outdoor Dry Bulb temperature of 110 degrees and indoor dry bulb of 80 degrees, with a piston metering device, suction superheat should be 0 degrees. But you don't want to add charge to a unit running at 5 degrees superheat or less. Instead wait till it cools off outside and charge to proper superheat at the new conditions.

I would think checking for proper air flow and sealed ducts would be the next step. Doing a load calculation would not hurt either.

[iraqveteran]

According to my Goodman/Janitrol charging chart, with an outdoor Dry Bulb temperature of 110 degrees and indoor dry bulb of 80 degrees, with a piston metering device, suction superheat should be 0 degrees. But you don't want to add charge to a unit running at 5 degrees superheat or less. Instead wait till it cools off outside and charge to proper superheat at the new conditions.

I would think checking for proper air flow and sealed ducts would be the next step. Doing a load calculation would not hurt either.

Checking for proper airflow is the FIRST step. Pressures should not even be taken until airflow is where its supposed to be. Cause without proper airflow, never gonna get good refrigerant charge readings.

The technician is obviously a part changer and not a troubleshooter. Lets try this and see what happens......no thats not it either, now lets try this.....


I can't stand part changers. Take your damn time and troubleshoot a system for once. 6 hours spend in one trip is a hell of a lot better than 6 trips at 2 hours each. What happened to taking your time? Everyone seems to be in a rush nowadays. Why? Your only moving backward when moving too fast. The tech needs to slow down and take the time to find the problem.

[udarrell]

I live in AZ and one of my Goodman 3.5 ton SEER 12 units (only 2-year-old) is having trouble cooling the rooms below '80F in daytime after running for at least 3 hours straight (outside temp 100 to 110F). Using a laser thermometer, the temp coming out of the vents varies from 64F to 69F.' My attic has R30 insulation. I've just changed the filter, and cleaned the condenser coils outside my house.

When the tech came, here are some measurements he took:

Sub cool: 11F / 10F
Superheat: 5F / 5F
Low side PSI: 75 / 77
High Side PSI: 280 / 260
Compressor: 22.1 - 18.3
Condenser: 1.6 -1.1

"NO Recorded CFM, NO Recorded wet bulb temps, ducts not checked for sizing, leakage & proper insulation, - all are extremely important in any diagnosis!" The blower wheel blades will usually tell you if evaporator is lint clogged. - udarrell

He told me those numbers look fine, and all he did is changing the piston from size 74 to 78 (according to him this will increase freon flow), and 'flush' the system.

Anyway, those didn't help at all, and now I have to call them back and do more diagnostics. What else can I ask them to look into (besides duct leaks)?

The other master techs in this forum have provided you with good information.

In that dry AZ climate, unless you live in an irrigated area, with 400-cfm per/ton of cooling (- CFM should always be checked & recorded on plenum!) , 80-Indoor db a 64-Indoor wb, 41% RH, the indoor temp split should be around 20.6-F, an 11-F split would be the target at 74-IWB, or 76% RH.

That information should be documented in writing as it is a huge signal of a problem to any qualified diagnostic HVAC tech.

Always ask the tech to make a record of all the test data & his observations, & keep all the install & service records near or on the equipment!

Another possibility is a hot-air-return intake leak, which would probably drive pressures higher than those recorded.

At 100-F & a 64-IWB the superheat would target at 3-F.
At 110-F & IWB 66-F it would target at 2-F superheat. Higher wet-bulbs, of course, will raise the superheat targets. - Darrell U.

[johndoe74]

The split temp at the air handler is found to be 20F (which the tech measured), but the split temp found in the room is 11F (amb 80F, vent 69F). Attic temperature is around ~120 to 125F.

This room's duct is the closest to the air handler, and yet rooms further away have a higher split temp (not by much though, around 14 to 15F).

I am guessing the attic temperature probably causes 4 to 5F loss in efficiency in the air ducts, but is losing 9F in efficiency means there's 99% chance there's a leak in the duct?

Of course, the tech could be lying with the split temp of 20F, I guess it's time for a second look.

[beenthere]

It could be pulling attic air into the duct. or it could be attic air being pulled intot eh room from the register.