[Maedie1]

Hey everyone, I'll cut right to the chase. Here in Miami, FL, we occasionally get cold fronts this time of year and the temperature will drop down to around 68 during the night. While it's cool, it's not cold enough to justify not running the a/c.

Unfortunately when these temperatures happen, the evaporator has a tendency to freeze up. I've read up on here and other forums about how a fan cycle switch can be used to shut the condenser fan off when the liquid line pressure drops below 170 psi for example.

I ordered one along with a separate contactor to wire the fan through. I wired the switch between both contractors and jumped the y terminal, added a jumper for the line voltage and moved the line going from the fan to the new contactor and left the other line going to the common terminal on the cap. This way when the pressure drops too low, the fan contactor will open.

I turned the system on and it's working fine now but the only part that concerns me is the fact that the compressor comes on first and the fan now waits for the high side pressure to reach 170 psi before the fan comes on. It's been rainy all day today, so the wet coil produced some steam when the fan came on after about 6 or 7 seconds.

My question is.. Is there any problem with this setup or should I scrap it completely? I don't see what kind of damage it can cause but maybe someone here can share insight. It's just getting old waking up to the coil frozen and having to thaw it out. The evap coil is clean and when it's in the 80s outside, the system can run all day and night, getting nice and cold with no freezing. It only happens when the ambient temp drops or when it's about 70 outside and rainy.

If this setup isn't going to be good long term, what is another solution? Also I should mention the unit was manufactured about 20 years ago. We had it serviced about 3 years ago and a small amount of refrigerant was added.


Thanks,
Brandon.

 

[pecmsg]

3 years between service?

At 68* and 70 indoors I don’t see the need for fan cycle. Something else is wrong.

 

[Maedie1]

3 years between service?

At 68* and 70 indoors I don’t see the need for fan cycle. Something else is wrong.

I should've been more clear. The service was basically a hard start relay being installed. We've had the coil cleaned sometime after that. If it was low on refrigerant, what temperature would the ambient have to be to cause the pressure to low enough for water to freeze on the evap?

 

[Snapperhead]

If you are sure theres no leak where you added the sensor .... then your setup sounds fine

Put some dish detergent on the sensor you screwed on the line looking for bubbles

 

[Snapperhead]

is the indoor coil nice and clean where the Air Enters ?

Can you shove your phone in a gap to take a picture ?

 

[Maedie1]

If you are sure theres no leak where you added the sensor .... then your setup sounds fine

Put some dish detergent on the sensor you screwed on the line looking for bubbles

That's a good piece of advice, I didn't think of that. I just went out and poured some soapy water and there's no bubbling.

I will get a picture of the evap later tonight. It's probably not squeaky clean but there's definitely good air flow and it only freezes at lower ambient. We have a couple vents closed in the rooms that aren't used and we have a separate unit for downstairs so this one only has to cool half the house. I believe it's a 2.5 ton.

 

[Restaurant Mech]

A standard household split ac should run fine down to 55 degrees.
I install a crank heater and a cycle switch for the systems I have here that run below freezing.

 

[Snapperhead]

Round here they will ice up when in the 60's ....

But anyhow , having vents closed only adds to the problem

 

[Maedie1]

Okay thanks for all the help. I will see how the switch works on this system and see how it goes. Where are you located by the way?

Edit: nevermind, I peeped your profile.

 

[Bazooka Joe]

t's just getting old waking up to the coil frozen and having to thaw it out.

That where a freezestat ( sensing indoor coil ) may help, but certainly you can see how the fan cycling control works.

 

[Maedie1]

t's just getting old waking up to the coil frozen and having to thaw it out.

That where a freezestat ( sensing indoor coil ) may help, but certainly you can see how the fan cycling control works.

Sounds good I appreciate the reply. I'll do some research on that since I've never heard of it.

 

[Bazooka Joe]

Sounds good I appreciate the reply. I'll do some research on that since I've never heard of it.

Thinking it was more popular in the ole days, I think Carrier among others used them a lot on some of their Residential and certainly Commercial lines. But like anything else, it cost money for the part and labor to install it at the factory which increased the price, even if it was an OEM option accessory installed in the field. As some here say it’s a race to the bottom. It was a sensing capaliary tube or the other type clipped onto a indoor coil outer bending tube, a snap acting disc.

 

[Snapperhead]

I carry Freeze Stats with me

I install those on units where the employees turn the t-stat down to 60 and I keep getting Frozen Evap calls

But , for customers who use AC when its cold out .... I install head pressure control , usually by ICM

ICM controller slows the fan speed down , instead of shutting it off

 

[Maedie1]

I carry Freeze Stats with me

I install those on units where the employees turn the t-stat down to 60 and I keep getting Frozen Evap calls

But , for customers who use AC when its cold out .... I install head pressure control , usually by ICM

ICM controller slows the fan speed down , instead of shutting it off

I've read about those as well but it sounded like a complicated solution. Could this only be achieved with an ECM fan motor or a standard motor as well?

 

[pecmsg]

Get the unit serviced and your issues go away!

 

[BBeerme]

What's the cut in pressure?

Most rookies set it for the minimum, like 35 psig differential. Should be 100 psig differential.

I always set R-22 to cut in at 275, and cut out at 175.

Hey everyone, I'll cut right to the chase. Here in Miami, FL, we occasionally get cold fronts this time of year and the temperature will drop down to around 68 during the night. While it's cool, it's not cold enough to justify not running the a/c.

Unfortunately when these temperatures happen, the evaporator has a tendency to freeze up. I've read up on here and other forums about how a fan cycle switch can be used to shut the condenser fan off when the liquid line pressure drops below 170 psi for example.

I ordered one along with a separate contactor to wire the fan through. I wired the switch between both contractors and jumped the y terminal, added a jumper for the line voltage and moved the line going from the fan to the new contactor and left the other line going to the common terminal on the cap. This way when the pressure drops too low, the fan contactor will open.

I turned the system on and it's working fine now but the only part that concerns me is the fact that the compressor comes on first and the fan now waits for the high side pressure to reach 170 psi before the fan comes on. It's been rainy all day today, so the wet coil produced some steam when the fan came on after about 6 or 7 seconds.

My question is.. Is there any problem with this setup or should I scrap it completely? I don't see what kind of damage it can cause but maybe someone here can share insight. It's just getting old waking up to the coil frozen and having to thaw it out. The evap coil is clean and when it's in the 80s outside, the system can run all day and night, getting nice and cold with no freezing. It only happens when the ambient temp drops or when it's about 70 outside and rainy.

If this setup isn't going to be good long term, what is another solution? Also I should mention the unit was manufactured about 20 years ago. We had it serviced about 3 years ago and a small amount of refrigerant was added.


Thanks,
Brandon.

 

[Maedie1]

What's the cut in pressure?

Most rookies set it for the minimum, like 35 psig differential. Should be 100 psig differential.

I always set R-22 to cut in at 275, and cut out at 175.

It's not adjustable, the switch opens at 170 psi and once the pressure increases past that, it closes.

 

[pecmsg]

It's not adjustable, the switch opens at 170 psi and once the pressure increases past that, it closes.

Who installed that?

 

[Maedie1]

I did myself after some research and reading other posts on this forum.

 

[BBeerme]

That's wrong.

You need to learn more about fan cycle switches.

It's not adjustable, the switch opens at 170 psi and once the pressure increases past that, it closes.