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Temperatures in my house have been climbing despite the A/C running.

My condenser unit is running, appears clean, and no brush is growing against it. The pipe into the ductwork above the heater is cold to the point it appears a bit of ice has formed. I cannot find a way to visually inspect the evaporator coil, but the ductwork where the coil should be mounted is cool. The fan is running, but air circulation seems to decline the longer it runs. I have replaced the heater's air filter.

The heater is a Trane XV95. The condenser unit is an American Standard manufactured in '95.

Any ideas what I should check? I'm leaning toward a fan control or evaporator coil problem.

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    A 28 year old unit, likely low on refrigerant, is the prime suspect to me.
    – Jon Custer
    Jul 13, 2023 at 17:20
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    "manufactured in '95" screams "leaking refrigerant". It also waves a white flag saying "I'm 30 years old, like it or not, I'm really close to the end of my useful life span" (hey it might be beyond its useful life span, but not by much...), and mumbles something about "newer units are much more energy efficient than I am"...
    – FreeMan
    Jul 13, 2023 at 17:21
  • Is there a way I can check coolant levels myself? Jul 13, 2023 at 17:41
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    Don't waste your money checking coolant levels. If a 30 year old A/C is spinning but not cooling it's time to say goodbye. Every penny you spend diagnosing it is wasted. Your time here is wasted. The coolant it needs is banned, you have to buy it black market, it costs a fortune and you know it'll leak out. Don't waste money looking for the leak. Also ... the new system won't last 30 years. Yes this sucks. Wailing, crying, tears of agony emoji.
    – jay613
    Jul 13, 2023 at 17:59
  • Repeating what Jay said: this is likely to be expensive to fix as it will need very expensive refrigerant on top of repairs with possibly difficult to find parts. Time to buy a replacement. If you haven't budgeted for it, maybe time to buy a window unit until you have the funding to replace the central. Sorry. If you want to try hacking it, you could adjust the fan speed tap way up and maybe get it to limp along until a bit more refrigerant leaks out.
    – KMJ
    Jul 13, 2023 at 18:07

2 Answers 2

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Definitely an iced-up evaporator coil (the part inside the duct, usually above the furnace).

The quickest way to de-ice it is to go outside and unplug or turn off the disconnect beside the outdoor condenser unit. This stops the flow of refrigerant, which is the source of cold that's making the ice, while leaving the indoor blower motor running. The blower motor, in turn, will help circulate indoor air around and through the frozen evaporator, accelerating its melt.

The disconnect is often a gray box within a few feet of the outdoor unit which looks something like one of these:

A/C disconnects

There's a condensate drain line that comes away from the evaporator. It's probably dry at the moment. Some time after the outdoor electrical disconnect is turned off you'll see a trickle and then a steady stream of water exiting this drain. Eventually it'll slow to a trickle again, and then nothing, and at that point the evaporator coil is fully de-iced.

There are several common causes of evaporator icing. Several commenters have already identified that the refrigerant charge might be low. Another common cause is restricted air flow -- if you haven't checked or changed the air filter in a while, do so.

If the system continues to ice then you have basically three options:

  1. help the system limp along by manually intervening to de-ice at regular intervals,
  2. have the system serviced to bring its refrigerant charge up to spec, or to check for possible blockage at the orifice or TXV where refrigerant enters the evaporator coil, or
  3. round up the spare change from the couch cushions and piggy bank and get a new system installed.

Be warned that icing is not only inconvenient, but it can also lead to a burned-up blower motor in the furnace. That motor is cooled by the air flowing through the system, so when air can't flow, the motor overheats. It should have internal overheat protection, but repeated cycling and operating at high temperature will destroy the motor in short order.

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Can you feel air blowing from the service ducts (registers) ? If yes, is it cold?

If it s not you have no cooling and need service.

If there is no air or little air blowing from the ducts, and your fan is running you probably have the evaporator iced up. You need to turn off the unit and allow the ice to melt.

Call for service because there is another issue, such as low freon that needs to be addressed and the unit checked for leaks.

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  • I can feel cold air when it starts blowing, but hours later there is barely any. I guess if the evaporator ices up it could be blocking airflow. I'd be interested to learn how low coolant results in ice. Do you know a good site I could reference? Jul 13, 2023 at 17:41
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    The physics behind low coolant causing freezing is not something for this forum but in a very simplistic way, the evaporation process that is supposed to occur at a certain speed throughout the evaporator occurs instead much faster and all at one end of the tubing where the liquid coolant enters so that area becomes very cold and the room condensate freezes before it can drip off. This causes reduced air flow creating a vicious cycle.
    – jay613
    Jul 13, 2023 at 18:06
  • Thanks, that make sense. Jul 13, 2023 at 19:08

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