A/C Issues

[BarkyardBQ]

We live in the desert with 100+ temperatures. Wife has been worried about the A/C dying since I met her, but it's survived 2 years so far. At the beginning of this summer it has started periodically (I assume) freezing up, and we have to turn it off for a few hours to and then start it up again. Does anyone have any experience with this, is there something we can try to fix or replace without fronting the cost of a new A/C?

[velocistar237]

Is this central A/C? By freezing up, do you mean literal ice, or just that it stops working?

[BarkyardBQ]

Central A/C, forced air.

It just stops blowing cold. It will continue to blow, but it's just air.

Also realizing after reading a few articles that we also installed a Nest last year. We didn't do anything with the Pro Setup and are using it's defaults. It has worked for September/October last year and only periodic issues this summer. Not sure if that could be a factor or or it's an issue with the unit.

[velocistar237]

You'd have to trace the electrical starting at the thermostat to make sure the correct signal gets to the compressor, then focus on possible compressor issues if the signal is okay. Start by double-checking or reinstalling the wire connections at the thermostat to make sure there are no shorts between wires or shorts to some grounding point behind the thermostat. It's tough to diagnose this sort of intermittent problem.

You'll probably get better answers in this forum:
http://www.doityourself.com/forum/air-conditioning-cooling-systems-126/

[BarkyardBQ]

Thank you. I'm researching what I can do.

[zolotiyeruki]

The most common issue with A/C units is being low on refrigerant.  That causes the evaporator coil (the radiator thing inside your air handler) to ice up, with literal ice.  Allowing it to sit for a few hours will allow the ice to thaw and the system will work again for a while.

Call your local HVAC tech.  They'll be able to give you a better diagnosis.

[adamj]

When was the last time you changed the filter? That can cause freezing issues as well and is a quick easy fix. While you're at the indoor unit take a peek inside (you should be able to see in with a flashlight where the filter came out) at the blower cage. If that's all caked up with dust and filth, chances are so is the heat exchanger and the indoor coils (evaporator).

While it's possible to clean yourself it's easy to screw something up, and a good HVAC tech can clean it a lot better than you can and you ought to get one out there anyway to give everything a check. He should hook up gauges to your outside unit to check the pressures, superheat/subcool, and figure out what is going on.

Other possible problems, low refrigerant (which is a symptom, not a problem; have the tech find and fix the leak) was already mentioned. Could also be a bad/clogged metering device, dirty evaporator... An HVAC tech has the specialized tools and knowledge to figure out what is going on and fix it.

[BarkyardBQ]

Turns out our A/C unit is 20 years old and while it still works amazingly we went through a few weeks of intermittent use and trouble shooting in 100 degree weather. The unit being so old was designed for a Mercury thermostat and includes a timer to deal with reseting the system. The Nest Thermostat has this feature built in and includes a 5 minute reset/delay. So the two timers were conflicting and the unit would only work when they were in sync.
After several service visits with three separate techs from two companies, the last tech noticed the extra timer and bypassed it as soon as he connected it the unit started blowing cold.