I recently replaced the capacitor on my external A/C unit. After replacement it started back up and was working fine for day or two but for the last 4 days it has been freezing up every single night after sundown. It's about 85 deg F. during the day and it runs fine and keeps the house at 70 degrees all day long. Air flow is normal and unrestricted all day. But almost immediately after sundown it starts to slowly freeze to the point where I have to turn it off and run just the fan overnight. I turn it back on every morning and it does the same thing. I have absolutely no clue what's causing it since the unit works perfectly during the day when the temps and humidity are at their highest, but after sundown it freezes.
My HVAC A/C is freezing after sundown every day
air-conditioningcentral-airhvac
Related Solutions
You may be looking at the problem backwards, the freezing lines could be a symptom of the problem not the cause. Start by looking for blockages in the system that would cause lower air flow / heat exchange.
- Dirty filters.
- Clogged ducts.
- Closed dampers.
- Closed/Blocked vent covers.
- Dirty coils.
Basically if the system cannot exchange the heat/cold, it will not function properly and could lead to over heating/cooling.
Frozen lines could also be caused by high or low levels of refrigerant, so you'll want to get a service person out to check the refrigerant levels.
Here is a really good image to visualize how it works.
Your question almost exactly sums up the situation I had at my home last August.
What I found then was that despite a properly sized air conditioning unit and what I believe to be good insulation (the house holds heat well during the winter), the unit still couldn't keep up.
I don't have full proof, but I think a few factors caused my situation and might be worth checking for you:
The condenser (outdoor unit) sits in an "inside corner" with the house on two sides of it and a chimney and small storage shed that partially blocks a third side of it. This prevents good airflow across the unit. [I can't do anything about this without relocating the unit, which is not a DIY job for me.]
We had very little wind at all during the heat wave, which also added to the lack of airflow across the condenser.
The condenser was visibly dirty, which makes heat transfer to the outdoor air less efficient. Lots of dirt, dust, pollen, grass clippings, etc. build up on the fins over time. Normally rain will clean it off somewhat, but we hadn't had rain in ages.
Despite some advice I've seen not to do it, I used a garden hose to wash off the fins of the condenser (it gets wet from rain, right?) very gently, taking care not to make it full of mud or to bend the fins.
I could see water evaporating immediately on contact, and I have an infrared thermometer I used that showed a 30F or so drop in temperature in short order. The AC performed much better after that, but we also started to get a gentle breeze that helped things along.
Related Topic
- What could be causing an A/C blower motor to turn off randomly
- Have to start the furnace manually every morning
- Why does the A/C “bump” and cycle super fast at night
- AC Unit Freezing
- Electrical – Why does the Goodman a/c blower motor randomly not work
- Why would the HVAC blower motor stop working after 10 minutes of runtime
- Does leaving the Central AC on all day and all night cause the motor to burn or compressor line to freeze up
Best Answer
A low charge can cause evaporator freezing. If your cap was bad that usually indicates an older system. Micro leaks have caught up, probably R22 and it is getting expensive. A 5 ton system will take 4-6 lbs normally to be fully charged but may give you another 5 trouble free years. In most cases the icing will get worse. It could also be a throttle valve that is sticking but it seems more likely low Refrigerant.