HVAC troubleshooting

In My Humble Opinion
1

Howdy gang, hope everyone is well.

I’m going to hire an HVAC guy to come check our system, but I was hoping I could get ahead on troubleshooting and get ahead of any issues.

We recently moved into a late 80s home and area going through a record setting summer. We have an upstairs and downstairs unit.

When it first got real hot I noticed the system struggling so I checked all the filters for each return–both were filthy and hadn’t been changed in ages. I also pressurewashed the fins on the units and cleaned tons of gunk out. Both of these had to make a big difference, tho I can’t tell.

The units act like they are caught up and will cycle off for periods of time–aka not running all the time.

The thermostats do not match measured temps with other devices. The thermo upstairs is set to 66 (all temps referred to are in F), the temp reading on the thermostat is 73 (actual temp at the thermostat is 76, as registered by an Accurite Unit). Temp in master bedroom is 79, the bathroom in the low 80s.

The AIR TEMP coming out of all the upstairs ducts is 55, which is where it should be. Stepping from the hall into the master bedroom is a good 5 degree difference. The further away from the upstairs return, the hotter each room gets, and the less air the duct puts out.

Our bonus room (Behind the master closet, above the garage) has but a trickle of air coming out. The closet, a bit more but barely, the bathroom, a bit more but barely, the bedroom, low air flow.

I think the upstairs could be re-insulated with modern foam, which could help.

DOWNSTAIRS: Air coming out of the vents is about 67, which is way too warm.

So I’m thinking: Downstairs unit needs Freon recharge.

Upstairs unit–I think we have a weak blower, blocked ducts, or detached ducts?

I have yet to get into the attic, as the trusses aren’t floored over so you walk directly on joists.

Any advice before I hire a pro? I say this because we’ve paid TWO for other service calls to be told the crawlspace was too small and they collected our money and left without helping.

Also a point of note: Our current electric bill is $586. Which is BANANAS.

2

Measure the temperature across the evaporator, or as close as you can get to it. You should be getting around 20 degrees. The upstairs unit sounds OK (55° outlet air is good). The downstairs unit might be OK (if the delta-t is 20 degrees), and have really bad ducts.
The thermostats need calibrating, but usually you can just live with their offsets.

How big is the house, and how big are the A/C units?

3

It doesn’t sound as if the airflow throughout your home is balanced and this could possibly be corrected with duct dampers but not knowing the configuration and accessibility of your duct system this is simply a guess. I’m confused over the ‘pros’ comment about your crawlspace being too small. Too small for what?

4

So I got up in the attic and I did some digging around.

First of all, there are huge air and light gaps on the exterior without any insulation.

The return unit (I don’t know the terms, the blower thing in the closet where I change the filter) has ducts spiderwebbing out.

At the one duct, the one near our bathroom, is losing cold air to the attic. See pic with my had.

I’ll add some photos from mobile.

5

This is the info on our upstairs unit. House is approximately 3000sqft
LINK

This is how the duct-work webs out from the return. Nothing is elevated or tied to joists, just piled on top of each other, defo some pressure on the bottom one. Is this bad or normal?

BTW the inspectors wouldn’t come up here NOT DUE TO NARROW entry, but due to the lack of floor boards. It really is a tightrope walk up here! The narrow entry is another space.

LINK

Cold air seeping from a bad joint job at the master bathroom vent. This is where the real serious decay in conditioned air begins.

LINK

Lots of broad daylight gaps all over like this. Tons of airflow. I hope this is something I can DIY spray foam. LINK

another air gap reading in an otherwise impossibly hot attic!
LINK

6

My elderly mother who we take care of cannot deal with the AC, even when it’s 105 outside, so I’ve closed the vents in her bed room and craft room.

Does that negatively impact the rest of the upstairs cooling abilities?

7

If the airflow is restricted too much the evaporator can ice over, which will cut your efficiency way down.

8

A couple of rooms supply ducts should be ok. Cutting off returns may cause icing.

OP, I would be cautious about pressurewashing condenser units–you don’t want to bend the fins over. A hose with a spray nozzle should be fine.

Change filters once a month, or at least every three months.

I agree with Beowulff-- 20 degrees across the evaporator is what you are looking for. If you’ve had duct cleaning in the past, the black plastic plugs they leave are good for inserting a thermometer.

9

Yes, don’t use a pressure washer! Regular hose only. You can pick up a can of spray cleaner for like $7 and it should cover a regular unit at least 2 seasons. If you want to do a real thorough cleaning, take the top and sides off (careful with the fan), get all the leaves out, you might need a grabbing tool or shop vac. Then spray the foam from the inside, let sit 10 minutes or so, wash, let dry, put it back together, and try again.

Because it’s a new home for you, I wonder if the unit is either underpowered or you need to mess with your registers.

If your bill is almost $600, I would call a pro at this point rather than DIY. The previous ones should not have taken your money.

10

It does seem like leaking ducts, closed hidden dampers, or just general balancing could all be factors. You can test general airflow/balancing by closing off the vents nearest the unit with good flow and seeing if it improves flow farther away. It’s also possible that the evaporator coil is clogged with dust and grime, reducing airflow and temperature.