Common A/C problems and fixes

[bonneyman]

When I went up to a house with an A/C issue my first step (after meeting the home owner and getting the lowdown on their issue) was to head to the indoor thermostat.

Most stats have a fan switch that's either "Auto" or "On". Switch it to "On". If the fan starts, you know several things right off. The system has power, so the power fuses and transformer are OK. The wiring between the stat and unit is probably OK, and the fan motor and wiring is fine. The problem is most likely the compressor unit (or section). Star there.

If the fan doesn't come on, it's something with the indoor (or fan) section.

[bonneyman]

Ask the customer did the cooling seem to slowly decrease over time, or did it just quit all of a sudden? A slow loss of cooling indicates a refrigerant problem (such as a leak or restricted metering device filter). A quick failure is most likely electrical (fuse, circuit breaker, switch, or wiring issue). This simple question will save you alot of legwork.

[bonneyman]

Noise complaints are a tough one. Usually the air noise is too loud so it affects hearing the TV, or hits that frequency that makes the person crazy. A noisey unit that was fine for years and suddenly gets a "whistling" sound is typically a dirty filter, or other an obstruction (like moved furniture) that is affecting airflow.

A noisey unit could be a vibration between the unit and the roof or wall of the house. Isolate the two with rubber pads or move the unit and secure it from moving. Weeds or branches could have been sucked into a fan, making noise.
Or it could be a heat pump going into defrost. While melting the accumulated ice on the outdoor coil pressure starts to rise. At some point that pressure will get to a point where it vibrates the unit. The defrost control may be defective, and not terminating the defrost when it should. Check the unit when it's making the noise - if the coil is free of frost then the defrost board or sensor could be to blame. Rarely it could out of adjustment, or a intermittent wind condition is preventing ice from melting.
Some things to check.

[bonneyman]

Intermittent problems can be extremely frustrating. It drives the homeowner crazy, but when you get there the unit is perfectly fine.
Start asking questions. Is it continuous, or just sometimes? Does it happen at a certain time of the day? Does it happen every day, or only on the weekends? Does it do it when it's really hot, or after the unit's been off while, or when it's been running hard? All of these questions (and others) can help you nail down what the offending issue is.

[bonneyman]

Studies suggest that 50% of A/C problems are a result of poor filter maintenance. Either the filter doesn't get changed regularly, or doesn't get cleaned often enough (or thoroughly enough). Plus, restricted filters cause freeze-ups and liquid refrigerant getting back to the compressor (as well as poor performance). Once this goes on for awhile other major things start failing.

Alot of people think that changing the filter once a year is sufficient. Not so. I recommended people change their filters monthly. When the power bill comes in - they won't forget to tell you the month has gone by!
"Oh, you're just trying to sell us more filters!" No. It's a "pay me now or pay me later" kind of things. Pay for a monthly filter (or cleaning), or put in a new compressor (or unit) alot sooner than you should. it's up to you!

[goodfellow]

Thanks for all the good advice George! During this last winter freeze our temps went down to the single digits. The outside unit handling my upstairs zone was cutting out regularly and throwing a thermostat code. After about 30 minutes it would start working again. Long story short, it tuned out to be a pressure switch.

Unfortunately you can't just buy one from a supplier around here -- you have to be a licensed HVAC tech to buy it. I found the switch on Amazon and ordered two of them because our downstairs unit may need one someday.

I now keep a stash on start capacitors, pressure switches, and a bulk tank of R-410A in stock. The 410A is getting ridiculously expensive and I was able to buy a 10lb tank at a great price, I jumped on it.

Word is the new systems will now use some kind of propane based refrigerant. -- ridiculous!!

[bonneyman]

Yes, as of 1 January the whole industry has been mandated to use the new refrigerant. It's called R-32, and the main issue I have with it is it's "slightly" flammable. Well, I've heard from my A/C supplier that some fire department jurisdictions won't go and fight fires at buildings with R-32 units. Explosive hazard. So, we'll have to see what unfolds.

[goodfellow]

Yes, as of 1 January the whole industry has been mandated to use the new refrigerant. It's called R-32, and the main issue I have with it is it's "slightly" flammable. Well, I've heard from my A/C supplier that some fire department jurisdictions won't go and fight fires at buildings with R-32 units. Explosive hazard. So, we'll have to see what unfolds.

I heard that the new R-32 stuff is just a propane based gas mix. It's bound to be flammable. Back in the day old-timers used to run propane in their R12 systems and they claimed that it gave the best performance; even better than R-12.

[bonneyman]

I wouldn't be surprised. The main problem with most of the "ozone safe" refrigerants is they lack chlorine, which helps with oil solubility. It also is what they claim causes ozone depletion. So - without chlorine - there's been oil return issues, clogging, compressor failing prematurely, etc.  Going to a hydrocarbon-based gas (like propane) would solve much of the oil solubility problems.

[bonneyman]

I used to find alot of units had marginal condenser fan airflow. I think manufacturers were trying to meet ever more stringent SEER standards, and were skimping wherever they could. One place was with outdoor fan motors.
They'd install barely minimum motor/blade combos in, and - when the temps got too high - the fans simply could not pull enough airflow through the outdoor coils. The units would have performance fall-offs, run all the time, and cooling became marginal.

One thing I did was put in a higher speed motor. Spin the blade faster - you get more airflow. This was easy on many units that had 825 RPM motors - you could just swap in a 1075 RPM ad wahlah! However, you can't get something for nothing. A 200 RPM increase translates to DOUBLE the needed horsepower! Thus, a 1/3HP 825RPM motor needs a 3/4HP 1075 to not overload the motor. (1/3 times 2 equals 2/3Hp, but they don't make 2/3 HP motors. Thus the need to go to 3/4 HP). You might have space constraints and the larger dimension motor might not fit, nor the fan blade be positioned in the venturi where it needs to be. Also, faster fans make more air "noise". A unit outside the master bedroom might make this objectionable. Thus this mod has to be on a case by case basis.

Alternatively, one could install fan with more blades (and/or sweep) so it could move more air. I had charts that would tell me what HP motor was required for such and such a fan blade for the CFM I needed, and I could play around with the specs on the charts to get a blade combo with the the highest CFM from the motor I had. Many A/C units have two-blade fans, so, going to 3, 4, or 5 blade fan could boost airflow somewhat without overpowering the motor.

Of course, this project is a bit time consuming, and most customers don't want to pay for the time and the cost of labor, new fan, and motor. I had a dentist that had a new 5 ton unit on his office, but it never cooled to his satisfaction. I told him this mod, and he went for it. Bigger more with a fan with more blades. Pressures were slightly improved on the unit, and - though it still wasn't as "icy" as he would have liked - the staff told me it was more comfortable in the late afternoon hours.

[bonneyman]

In the old days we'd get systems where the outside unit is clicking, or starting and stopping, or runs fine for awhile and then stops. Come to find out there was a voltage drop in the stat wires, and if it went below minimums for the contactor, it would drop out. Too long a wire bundle (over 60 feet), or cheapie bundles with 22 gauge wires (instead if the older 18 gauge), or old bundles that were corroding/deteriorating. Just R&R ing the OEM contactor might not solve the issue. And running new wires could be tough (or impossible due to routing), and expensive.

This is one place where electronic controls could be a solution. Most electromechanical 24v contactors won't operate reliably below around 18 volts. But electronic contactors will. Might be the only affordable way to get an older system running right. But not cheap.
I never got to actually do this because the electronic contactors were relatively new when I left the industry. But man I sure could have used this thing during my career.