Tuesday, June 13, 2017

No Time -- And The Air-Conditioner Is Fading

     Up early and out of time already.  I spent some of the morning dealing with a frozen-up "A" coil* and now I have to get in the shower.

     Low working fluid, again.  I'll have to call the HVAC tech, and sooner rather than later.
* Why is it an "A" coil, and does that make the one in the compressor unit outside the "B" coil?  It does not.  The shape of most of them, set to allow maximum contact with the air flowing by, is like a capital lambda; larger ones may have a cross-brace, and this, seen end-on, forms an "A."


B said...

Put a timer in the contactor circuit..... adjust the duty cycle so that for, say, 6 minutes out of every half hour the compressor is shut off but the fan still runs, giving the coil time to warm up and melt.

I've done this on marginal systems, and it works.



Roberta X said...

Turning up the thermostat works, too. Your method risks short-cycling, which can kill the compressor. $$$.

B said...

Not really, as it goes off for enough time for equilibrium to take place (Why I specified 6 minutes). And my method works even when you aren't home (or are asleep) to cycle the thermostat. Plus the fan stays on, removing the melted ice by evaporation.

Your system, do as you wish.

Roberta X said...

No, really, B: if your timer kicks out thirty seconds after the 'stat has called for cooling? Not good. I have very long coolant lines in the big systems at work and short-cycling kills them *fast.* You get "slugging." The 20' at home? Not so bad, but it's still not what the thing is designed for.

I managed it by increasing the setpoint gradually once I defrosted the coil, and that, plus fans, kept us okay until the tech got here and recharged the system, 24 hours after I realized we were in trouble.

Fuzzy Curmudgeon said...

You could call the outdoor coil a "C" coil, though...since it is the condensing coil 😁

B said...

As you say.

Unless your timer (I used a couple of 556 chips) STARTS at the call for cooling, and then does the duty cycle thing as long as the thermostat calls for cold. If the stat is satisfied, then the timer is off. No worries about your scenario. You are a good enough engineer to create a similar system that won't slug you cooler.

I realize all engineers have Not Invented Here, but my idea works, has for years on several undersized systems and you shouldn't reject it out of hand before you consider it.

As I said, your system, do as you wish.

What, exactly, do you think freezig the A coil does to the compressor?

Make no mistake, no solution will fix low freon. IIRC, you've had this issue before.