Fan cycling help.......

[Elite-Mech]

Hello All, I am a contractor in southern California and needed some help from you professionals about installing a fan cycling switch. I installed a small custom four drawer 1/2 HP r404 system around summer time. I haven't had any problems with system until now. The customer calls and says product is freezing. The system runs only on LPC and no defrost timer. I sized condenser for 110* ambient conditions, but now that's reaching 40-55* at night and 60-70* day time is it a good idea to install condenser fan cycling switch to keep HP up? I don't want to mess with LPC settings because I don't think that's the solution. I've been in trade for 15 years, but never had to install these only troubleshoot. Any input would help, thanks in advance.

[cuchien]

Elite-Mech, I think intalling a headmaster would be better for the longivity of the system given the temperature swing you have there. Put a fan cycling switch in and set the cut out pressure at around 90F doesn't hurt either. If you don't have any sort of HP control, you'll be replacing that compressor pretty soon. Also, is this a cooler or freezer? It sounds like a freezer (404A) and you don't have a defrost timer? Strange. Good luck.

[Elite-Mech]

Elite-Mech, I think intalling a headmaster would be better for the longivity of the system given the temperature swing you have there. Put a fan cycling switch in and set the cut out pressure at around 90F doesn't hurt either. If you don't have any sort of HP control, you'll be replacing that compressor pretty soon. Also, is this a cooler or freezer? It sounds like a freezer (404A) and you don't have a defrost timer? Strange. Good luck.

Its a cooler

[itsiceman]

If it is only on LPC it would reach cut out sooner with low head.
If you are going to change something I'd go with a tstat
Is it only one evap?

[jimmytee]

Sure you could install a fan cycling switch in there. I try to maintain 90- 100 degrees condensing temperature. A head master would be a better answer. I don't like the temperature /pressure swings with fan cycling, but it will serve the purpose. So I take it that this has a remote condensing unit? Or is this a self contained box outside? Typically, running a condensing unit in low ambient conditions without low ambient controls of some sort ,results in the unit running as though it were low on charge. The result with pressure controlled temperature is that usually the box won't get cold enough, because one the pressure control shuts off early due to the low charge like situation and or the evaporator is not fully effective for the same reason. Are you sure there are not other reasons?
On larger equipment, I've all but abandoned fan cycling in favor of electronic modulation of the condenser motors.

[MicahWes]

If the head is dropping too much at night, I can't see why it would freeze product?

[2sac]

If the head is dropping too much at night, I can't see why it would freeze product?

Agree. If anything, I think it would short cycle.

[jimmytee]

Agree. If anything, it would short cycle

Essentially that's what I said, with a little more info

[2sac]

Essentially that's what I said, with a little more info

I like to keep it simple LOL

[kklobas]

it would work and be easy to install. i have them on walk ins in jackson wy and see 10 to 20 below zero nightly.

[Snapperhead]

the easy fix is adding a fan switch to turn fan off at 200 psi and lower

Sometimes it gets confusing when setting it up , because you want it to come on 200 and higher

[kklobas]

on 200 off 250 works pretty well

[powell]

For a typical 4 drawer under counter refrigerator I think the 1/2 hp system is oversized. Added to that, you're gaining about 35% btuh capacity at a 50 degree ambient versus a 110 ambient. The LPC is probably set at a cut out just above freezing the product during higher ambient temperatures.

With that said, I would think that there is too much sub-cooling at the lower ambient temperatures. If it's a TXV system then the TXV will be oversized even though the pressure drop across the valve is less. The extra subcooled liquid refrigerant and the LPC settings are probably what's causing the freezing of product.

I'd install a FCC and temperature control.