AC freezes up, but only on the same day, once a week.

charliechicago

Hello to all,
I replaced an old R22 condenser last year at the end of September. I left the furnace and inside coil. I charged the new unit with MO99. It froze up a week or so later and I came back and the pressures and super heat were fine. It has frozen up two more times this year. Pressures are always fine when I come back. Now here's the deal; the system only freezes on Saturday. The family is Jewish and they observe the sabbath. That means from sun down on Friday until sundown on Saturday, they don't adjust the thermostat. They leave the oven and a flame and a pot on the stove continually for 24 hours. It has never frozen during the week.
They had no problems over the winter with the blower. The blower always seems to be running. The only thing I noticed is that there are only three wires to the tstat. There is no G. The blower comes on through y I guess.
Any suggestions?

nicholas bonham-carter

Maybe the constant boiling pot is over humidifying the air inside?—NBC

HVACNUT

Did you do a triple vac and replace the liquid line drier?
Was the old compressor a burnout? SLD?

Air filter, evap and condenser coils clean?
All supply registers are open?

What's the equipment and metering device?

The pressure's aren't always fine. Otherwise it wouldn't freeze. Are there pressure switches? Are they rated for R22/MO99?

ratio

Check airflow, first of all. My guess is marginal airflow (or even adequate but on the low side), coupled with extended runtimes on the Sabbath due to the addn'l heat load of the oven etc.

A freezestat on the suction line as close to the coil (inside the box even), breaking Y, might be the best solution.

ratio

Check airflow, first of all. My guess is marginal (or even within the numbers, but scant) airflow, coupled with long runtimes due to sensible & latent heat from the oven, etc. is slowly cratering the temperatures. Or even someone throws a towel over an air device on Friday so it doesn't blow across them all Sabbath long!

A freezestat, placed on the suction line as close to the evaporator as possible (inside the box even), breaking Y, might be the best solution. Possibly the only solution.

Ironman

Probably has marginal airflow as ratio said. That, plus operating overnight at low ambient temps is causing the suction pressure to drop too low thus icing the coil.

A low ambient head pressure control like an ICM 326, a suction line freeze stat like ratio said, or just simply setting the thermostat a little higher on Friday before sun down are options.

What type of metering device is on the coil?

HVACNUT

This pot of water does have a cover, right? I don't see it having that much of an effect. Not enough to flood the coil anyway.

GW

Can you check the pressures on a Saturday? Seems like you’re connecting the dots. I sure hope you left yourself a back door / escape route- why not change the coil and line set? Oh- they don’t want to spend the money? Ok then make sure that’s not your fault. I sure hope you offered that as an option. I’ve never done a drop in ref, I’ll let the nest guy handle that job

ChrisJ

Doesn't MO99 have a slightly lower boiling point than 22? What expansion valve is in it?

pecmsg

Need exact #’s
Superheat
Sub cooling
Air Flow TESP

I prefer R-407C over MO99

unclejohn

Are they or someone in the house turning down the tstat Friday evening and then not touching it again until Sunday. I haven't even turned my A/C on yet. Gets kinda chilly up there in the evening I would guess.

Matt_67

I think unclejohn has it with the chilly evenings. My guess is the oven and burner are causing the A/C to run in the middle of night when it’s cold outside. The head pressure drops and the suction pressure follows it causing the icing coil. A freeze stat is probably the easiest solution short of low ambient controls on the condenser.

motoguy128

I agree with others, the AC is likely icing up overnight with the load of the oven and pot.

4 solutions,

1) a low ambient kit, just a pressure switch added to the service valve that cycles the outdoor fan.
2) antifreeze switch that senses suction line temp indoors at the coil and breaks the call for Cooling to condenser but keeps fan running
3) outdoor temp switch that prevents condenser from running below an outdoor temp of maybe 55F.

What have the Overnight outdoor temps been in these situations? In the spring it’s usually in the 70s off 80’s and sunny for a high but 40s and 50s overnight.

mattmia2

So, is the a txv or an orifice on the evaporator? i can see the cool outside temp and the constant cooking loads pushing an orifice system in a bad place.

Erin Holohan Haskell

@charliechicago, we've merged your two posts here.

EBEBRATT-Ed

@charliechicago

What do you consider good pressures? Around 57 psi suction is freezing temp.

Probably needs a condenser fan speed control or fan cycler.

Low pressures cause as many problems as high pressures.

Ironman

The P/T chart for R438a (M099) shows that 62psi is 32*. Thats 5psi higher than R22. If you're assuming that the low 60's is good pressure for M099, then you're in error. Also: if you have a TXV, then its powerhead is charged with R22 and it will be somewhat effected by the different pressures of M099.

However, I still believe the main issue is them running the a/c overnight during low ambient temps.

mattmia2

So you need a txv for the frankenrefigerant. Or low ambient controls on the condenser.

ChrisJ

> @mattmia2 said:
> So you need a txv for the frankenrefigerant. Or low ambient controls on the condenser.

If it's a txv and the txv is running 5 degrees too cool low ambient controls aren't really the right fix. That will keep the liquid pressure up, but the txv would still be throttling it wrong.

I guess there's chance the txv is running wide open and being starved when it's cool out but I'm betting not.

HVACNUT

I go back again to the steps taken for the swap out.

Was this an issue with the old condenser? Probably not.

charliechicago

Thank you all for your responses, its been very helpful and much appreciated. It is an orifice, so it makes sense that it could freeze.
Can someone give me the info/specs on a freezestat? Never used one before. What controls the off cycle? I'm thinking Johnstone or United refrigeration would have it in my area, NJ?
Thanks.

ChrisJ

charliechicago said:

Thank you all for your responses, its been very helpful and much appreciated. It is an orifice, so it makes sense that it could freeze.
Can someone give me the info/specs on a freezestat? Never used one before. What controls the off cycle? I'm thinking Johnstone or United refrigeration would have it in my area, NJ?
Thanks.

I would use either an ICM325 or ICM326, you'll have to decide what is best for your application. Also, I'd swap the condenser fan motor out for a better high temp ball bearing motor. The way these controls work is not nice to the motor windings. They work really nice, just the motor hates it.

https://www.icmcontrols.com/documents/ss_LIS118-2.pdf

The freeze stat is just a cheesy bimetal switch that clips to one of the suction tubes on the evap and opens the connection if it gets too cold. So it would typically go inline with the 24Vac to the outdoor unit. It may be a good idea to wire an ICM delay in line with it unless the outdoor unit has such built into it's control board.

mattmia2

If it is orifice and you didn't change it, it is likely the wrong orifice. It would be a better idea to put in a txv for this refrigerant or an adjustable txv.

charliechicago

HVACNUT it was a leaker. Pulled a good vacuum and charged.
MATTMIA2 I was thinking of recovering charge and putting in r22. Think that would help?
Thanks to all.

mattmia2

Real r22 would probably make all your problems go away, but definitely see what others think.

ratio

How confident are you that it was working before you changed out the condenser? Is it possible that it hadn't worked right for some time? How long have they lived there?

JUGHNE

It seems the simplest would be a ODT that keeps the comp off below 60 or so.

You mentioned the blower seems to always running.
With out a G wire, if the call for fan is from the tstat then the Y would also be hot and AC on. If the blower is on because of blower time delay off from the board, that is normal. IMO

Could you run a new tstat cable of 18-6 or 18-8, install a 7 day programmable tstat to reduce overnight cooling.
Also some have random fan on properties for recirc purposes.
There might be some with ODT sensor that would lock out the AC on a cool night.

mattmia2

pecmsg said:

Need exact #’s

Superheat

Sub cooling

Air Flow TESP



I prefer R-407C over MO99

Ironman said:

The P/T chart for R438a (M099) shows that 62psi is 32*. Thats 5psi higher than R22. If you're assuming that the low 60's is good pressure for M099, then you're in error. Also: if you have a TXV, then its powerhead is charged with R22 and it will be somewhat effected by the different pressures of M099.

However, I still believe the main issue is them running the a/c overnight during low ambient temps.

So I didn't see answers about how you were calculating the numbers being fine. when you were measuring the wet bulb return air and the outdoor ambient and figuring out what superheat you needed, did you use a pressure/temp chart or instrument with the chart baked into it for the refrigerant you were using or was it for r-22? If you charged it using the r-22 chart you would have undercharged it because the temp from the r-22 chart would lead you to set too big a superheat which might cause the suction pressure to fall below freezing when the outdoor ambient falls near the lower operating limits.

clammy

Don’t use a pressure switch for head pressure control for low ambient they do not work so great and tend to rack the condenser coil instead use as Chris j suggested a icm 925 head pressure controller ,I de also second the freeze stat on the suction line at evaporate and if ambient outdoor ambient is that low I would suggest a crank case heater for you compressor to help prevent oil slugging . I would also make sure you have a time delay on the condenser giving it some time between cycles .I usually pass on replacement 22 refregerant on ac if one or 2 of the components are shot condenser/ evaporator I just quote a replacement otherwise you get the head ache and a upset HO and a bad reputation for trying to save the customer some money and lose any money you where gonna make . Just my 1.5 cents . Peace and good luck clammy

EBEBRATT-Ed

@charliechicago

A freeze stat in this instance is a band aid covering up the real problem

charliechicago

Thanks again to all who responded. I ended up putting on a Ranco temperature control, strapped it to the suction line. Set for 10 minute delay and have not heard back!

ChrisJ

charliechicago said:

Thanks again to all who responded. I ended up putting on a Ranco temperature control, strapped it to the suction line. Set for 10 minute delay and have not heard back!

EdTheHeaterMan

me too