Weird HVAC problem - Need advice
 

Ok guys need help with a strange problem in a rental property I own.

Property is a 2 bedroom townhouse build slab on grade (no basement or crawl space). Place was built in 2006.

About 2-3 weeks ago tenants came home from being gone for the weekend to find the main level wood floors popped up between the kitchen and closet that contains the HVAC unit and water heater (about 4 feet apart). Wood floors are on concrete slab.

Tenant (who is handy) noticed the HVAC unit was not draining at all (A/C running all the time, it's 95+ degrees typical Colorado front range summer).

HVAC guy (who I have used for a few years and seems sharp) checked everything out, cannot find a leak. Determines that for some strange reason the A/C is cooling normally but is not pulling humidity from the house. Ambient humidity in the main level is 55-60% which is crazy high for Colorado. He comes back again the next day, investigates further, cannot find a leak in the condensate drain, but notices it's also not generating anything to drain. He recommends we call a plumber.

Plumber comes (same deal, good guy I have used for a few years) and looks high and low, cannot find a leak. Points out that the inside HVAC unit is a Trane (replaced by previous owner) and the outside unit is a Rheem (which appears to be original/2006). His conclusion is the water (or high humidity) is due to the HVAC unit, but that there could also be a hidden pinhole water leak, such as underground drain pipe or sprinkler percolating up through the concrete slab, especially if it was not properly barriered when built.

I tell the plumber that my HVAC guy has gone through the unit and it's working fine, but he can't figure out why it's not condensating humidity in the house. Plumber recommends we call a Leak Detection specialist.

Leak detection specialist comes and does a 4 hour examination with cameras, pressure testing, and infrared. Charges $500 for the evaluation (which is fine with me) and determines there is no water leaking anywhere. His conclusion is the problem is that the HVAC unit is not pulling humidity out of the air.

Back to the HVAC guy who says he cannot find anything wrong with the HVAC unit. He has called his other HVAC guy buddies, as well as Trane, and says no one has ever heard of such a problem.

At this point I am thinking just replace the HVAC unit, inside and out, with new matching units and see what happens. Problem is that this is an expensive "trial".

For now I have a dehumidifier running in the space which is helping the wood floor start to lay down and has reduced the ambient humidity to around 35-40% which is what it is in my personal home w/ A/C running right now.

Sorry for the long saga, but can anyone in the braintrust help explain why an HVAC unit would not pull humidity out? My HVAC guy says it's working normally, shows a normal Delta-T (whatever that is) and is appropriately sized for the unit.

Thanks in advance for any suggestions before I spend $8000 on a new HVAC unit here that may or may not actually fix the problem.

Is there an access port? I would love to see a thermal temp reading of the coils. I would also look at electricity consumption.

What model Rheem? Unless it is a multistage unit, most models don't care if the evap is a different model. I would also look at the TXP.

If the evaporator coil is cold and has air flowing through, pretty hard to imagine the coil would not be condensing water from the air. Is the blower speed way too high?

Have you tested that the HVaC coil is draining and not plugged? It would probably ice over if it was, but I’d verify that.

Icing over is something I'm wondering about, but that usually means the freon is low.

Is it "short cycling"? Starting a lot, but only running for a short period? That could be a thermostat/control issue.

Just a thought. Get a piece of plexiglass cut the same size as the cover for the air handler. Run the system and watch what is happening. The condensate might be getting sucked back into the airstream and added to your house instead of flowing down the coil and into the pan.

Check your return temp and then check your supply temp a the register closest to the air handler/furnace. My guess is you have hot air infiltrating the return. Another guess on the no condensation from drain is that the condensation is lifting off the coil due to static pressure.

Was going to suggest the plexi cover too. You'll be able to see moisture forming on the coil as the unit runs. If it's not making it to the drain, it's probably lifting. If it's lifting the only way I can think of to verify would be to remove one of the metal covers for the coil and put plexi in place. Do you know if it is an A coil or N coil?

Good call. I can see that happening if the coils are dirty/ tenant has not kept up on filter changes.

Thanks guys I will run these great ideas past my my HVAC guy. I like the plexiglass idea. Also hot air into the return would make sense, but not sure where that would come from would have to trace the returns. I don't think they go through an attic at all they way the place is laid out.

The filters are clean and my HVAC guy says the coil looks clean. He does not think freezing is an issue.

If the evaporator coils and fins are clean, not icing over the delta temp between the chiller and ambient is in range, no way is humidity not being removed. Is basic science fact.

What is the air temperature drop across the evaporator coil?
What is the R/H of the air returning to the air handler?
What refrigerant and what were the pressures?
What is the temperature of the refrigerant leaving the evaporator? (suction line temperature)
What is the temperature of the refrigerant entering the air handler? (liquid line temperature)

Horizontal or vertical air handle or indoor unit?

It is possible that the air velocity is too high and the air isn't in contact with the evaporator long enough to wring any moisture from it.
As mentioned above, too high of velocity could also pull the condensate off the evaporator but you should be able to detect that by seeing some moisture in the supply ducting.
Did your HVAC guy leave behind a work order with his findings?

Is the thermostat fan switch set to ON? If so, when the compressor cuts out and the fan still runs, you'll put all of the moisture you just pulled out of the air (or at least some of it) back into the air. The fan should only run when the compressor is running.

Not really. With a properly functioning AC system, there's no problem with running the fan continuously. In fact on some 2 story homes it can actually increase comfort by decreasing the temp difference between the first and second floor.

I think it might depend on how much moisture is in the air and how well the evaporator drains.

Check the attic, see if a return duct is compromised.
A WAG (Wild Ass Guess) air is not being pulled from the cooled space.
Or they will find water is condensing on the coil, but a hole / open seam in the drain pan is letting all the water out before it makes it to the drain.

Absolutely. On our old home, we did that during the spring and fall because otherwise the upstairs would be hot and the downstairs (where the thermostat was) would be cool, and the AC would rarely run. For a few year, I'd just run the fan in the on position during those times of year when the outside temp created that condition. I eventually found a thermostat where I could schedule the fan to run periodically outside of the AC running.

I'm with the others. If the house is being cooled, then the AC has to be condensing the moisture out of the air. Then that is somehow getting back into the air. I'd want to check out the HVAC myself. I'm no expert, but as a home owner, I determined that lots of HVAC guys (not saying your guy is one of them) are hacks.

We had all sorts of minor issues with the system in our old home over the years, most of them were due to incorrectly setup draining.

Not quite. An oversized unit would cool the space faster than it can remove humidity. You'd end up with a cold humid space. Would go back to what Redbeard was talking about with short cycling.
https://energyair.com/signs-ac-system-large/

BTW, In my old house my (by old I mean age. I still live here) 2nd floor will be a bit colder than the first floor. I sized the ductwork to the second floor to handle cooling load. I have to shut the registers off almost completely in the winter.

Point taken. I do remember reading about how for them to be most efficient, they have to run at least X long (5 mins or 10 mins, I think, can't remember which).

The short cycling is an interesting thought. I know it's a modern Honeywell thermostat that has a recovery mode between cycling so that many not be possible?

Today we lowered the max blower speed to see what happens. That was Trane tech support's only idea to try. Will see if it starts draining at all.



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If you're dropping the fan speed I'd probably watch your suction temp for a little while to make sure you don't frost the coil due to inadequate air flow. I'd think as long as you went from High speed to either medium high or medium (assuming 4 speed blower) You should be fine.

Just out of curiosity, what is the A/C size? 1.5-2 ton?

To add - as your OP - this situation is a recent development, there is something new that's going on.

Update - Basically everything you guys have suggested above has now been checked out by my HVAC guy (thanks for the recommendations, I passed them along) and it is all showing normal.

He did get in touch with the next level of tech support at Trane (engineers) who recommended he look at the TXV valve. They asked for some data off the unit and he took readings today and forwarded it to them, waiting to hear back. Replacing the TXV may require us to upgrade the unit to R-410 from current R-22, if that turns out to be recommended.

Normally a faulty TXV will show up in operating pressures. I'll be surprised if it's a bad txv.

Agree^^^^^^ that's the whole point of throttling back the high pressure gas to low pressure liquid. So if that delta between high side coming in and low side remains in range, the evap has to be almost ice. The tech needs to let the system run with gauges/ probe connected for 15- 20 mins to make sure the TXV remains constant in pressure differential.

My recent situation proved this out as initial cycle would be fine, then the low pressure side would start falling off after 20mins or so

BTW, a new txv shouldn't necessitate switching to R410. I recently did a txv swap on a 25 year old Carrier R22 system. You can still find the R22 txv's it's just a matter of pulling the part number off the existing txv and doing an online search or talking to a parts supplier who can cross reference the old number. It might require some new piping depending on how the old txv is connected in the system but it can be done.