HVAC (residential) questions

[andrew whicker]

Hi,

I've been troubleshooting my house HVAC system (R22):

In June my line started freezing. I had a tech come out and we cleaned the condenser coil, changed the filter (even though it wasn't super dirty - I changed it once a quarter), he checked the pressures and everything seemed okay. I was at the low side of pressure, but I was pretty close.

Then the line froze again. So then we added a pound of R22 ($ 300 / lb). Everything ran for a month.

Line freezes again. I did a big clean up then.. so I cleaned the evaporator coil, really cleaned the condenser coil, removed the blower fan and cleaned that off. I measured the motor amperage draw (4.4 amps vs 4.9 amps on motor nameplate). I ordered a Nest thermostat.. will be here today.

It is freezing very slowly compared to how quickly it used to freeze so I feel like I'm right on the cusp. I'm debating ordering a new motor ($ 160). The old one is pretty disgusting looking, but the amp draw seems to be fine? The bearings feel good too.

I was also going to check for leaks using soap bubbles.

Questions:

- Has anyone had their system swapped out for R407c? How did that go? Seems like a very sensible route to take. I'm irritated the tech didn't tell me about 407c as a replacement.

- When the tech captures R22 when they evacuate the lines, how much if are they are able to capture and re-use? I.e. the tech tells me replacing any component in the system is going to end up costing more or the same as a new unit after the cost of R22. However, they are capturing the R22... so unless they are really bad at capturing the gas, couldn't they just re-inject the R22 back into the system plus a few pounds of inevitable losses during the process? And this isn't even taking into account that R407c is $350 / 25 lbs! Which is MUCH cheaper than R22!

- If changing from R22 to R407c, it sounds like oil is an issue. However, it sounds like there are two different replacements: R407c and MO99 which use different oils depending (POE vs mineral from what I can tell). But even if oil is an issue, it looks like I can replace the compressor ONLY (not have to get a new coil and housing), correct?

- Would a new control board have any impact what so ever? I found a replacement (NOS) for $ 60.

- My motor (Emerson k55hxkps 9737) is labeled as a 4 speed motor. However, the only thing I've been able to grasp from online manuals, etc is that there are two speeds from the control board: heating and cooling. I'm assuming my motor speed wiring isn't an issue since the AC has been working fine for a number of years. But just something else I wanted to check. The motor nameplate says 1075 RPM @ 110v & 5 amps. So this is the highest speed?

I have a RPM measuring tool (using the reflectors on shafts) and will try to check final speed under load (ie. while it is installed) today.

[Doug Garson]

Have you ever heard of a device called a Coolbot? Not directly applicable to your situation but one of it's features is it monitors the coils on a window AC unit and shuts it down when the temperature gets too low to prevent freezing. Perhaps you could add something to do the same ie monitor the coil temperature to prevent freezing.https://www.storeitcold.com/

[Rick Potter]

A price comparison for what it's worth.

Last week I had a new condenser unit replacement installed in a rental. It cost me $2800 installed, and was pre-charged. I got a couple hundred off because I know the installer, but that seemed pretty reasonable anyway.

He told me they are phasing out the older units that already phased out the real old stuff, and repairing them was not really advantageous anymore. Sorry, I don't remember the size, but it is serving 1500 sq. ft..

[andrew whicker]

That sounds very reasonable for a new condenser w refrigerant.

However I've been getting the "r22 is too expensive" line and now I find out there is a cheap and well understood replacement

[Tom M King]

They are not allowed to use recovered refrigerant in another owners equipment. With a new, clean recovery tank I don't worry about reusing it in my own stuff, but it's not likely they have one they're willing to use for this for any particular customer. Maybe if you offered to buy your own recovery tank they would, but it wouldn't surprise me if their company had a policy not to do that.

All our units use the same refrigerant so I don't mind reusing it if it tests okay at pressure for a given temperature. I don't work on other peoples HVAC equipment, and make no claims to be a pro at it.

An R22 unit must be pretty old by now. The last system I had any friends who owned one had it replaced a few years ago. It was getting not only really expensive to get anything done to it, but kept having to be worked on every season.

I expect a lot of them won't have separate equipment for each refrigerant, but I only run one kind any any of my gear and won't hook any of my stuff up to anything else.

[Tom M King]

I just read a little about making the refrigerant swap. I wonder how effective flushing the system would be. You can't mix refrigerants and different refrigerants don't like the different kinds of oils used. I think to do this a tech would need a whole set of equipment dedicated to just doing the swap and I can't imagine many being willing to make the investment. I certainly would not do it with mine.

[andrew whicker]

I get it. However, it looks like it is a fairly common swap for HVAC companies. I see it being done quite a bit whenever I find myself on an HVAC professional forum.

[Tom M King]

Probably call around and find someone that does it. I wouldn't expect them all to do it. I also looked at the pressures and 407c runs 11% higher and lower than R22, so that's expecting a little more out of old equipment. What year is the system?

[andrew whicker]

I'll get all the mfg details..

[Bruce Wrenn]

If you have pleated filters in your air handler, get rid of them! Freezing is usually caused by too little air flow over evaporator coil, or low charge. Friend's house at beach, downstairs unit froze solid, including condensate pump. Condensate tray was 4" deep in almost frozen water water. Had to bail it out. Shut unit down, opened unit up and placed fan blowing room air across "A" coils for couple hours, then shifted unit to heat mode to completely melt ice. A couple weeks earlier, daughter had replaced standard filter with a pleated filter. Put in a standard filter. That was three summers ago, and unit hasn't frozen since.

[Bill George]

So is it an air flow or what are you setting your Tstat at overnight. Set to low and the outside temp drops, the pressure on the low side gets low enough to freeze the coil.

Air Flow how did you clean your evaporator coil? They are very difficult to get clean while in the unit. Must be inspected on the air entering side and cleaned.

Blower wheel fins have they been cleaned of dirt in the C curve? Most blowers need to be removed from the unit and the motor made waterproof or removed and pressure cleaned or scraped clean one fin at a time! Has someone in the house closed dampers on the registers or ductwork?

Putting in a larger direct drive motor does nothing unless it turns faster, most have fixed speeds, 900, 1100, 1275 and so on to select from.

Here is a direct replacement refrigerant that needs nothing, my son who still works in the field has used it at times, and he is doing like I did for 25 years commercial and high$$ residential. Read >https://www.freon.com/en/products/refrigerants/mo99


I just read Bruces response above but the Tech should have caught that pleated filters are to restrictive for the older units. My 96% unit can use pleated as it has a variable speed ECM motor that ramps up to over come the resistance.

[Bill George]

I just read a little about making the refrigerant swap. I wonder how effective flushing the system would be. You can't mix refrigerants and different refrigerants don't like the different kinds of oils used. I think to do this a tech would need a whole set of equipment dedicated to just doing the swap and I can't imagine many being willing to make the investment. I certainly would not do it with mine.

https://www.freon.com/en/products/refrigerants/mo99

Screenshot_1-8-2024_16842_www.freon.com.jpg

[Tom M King]

I hadn't seen that one. All our units are 410a and I'm sticking with that as long as I can.

[Bill George]

I hadn't seen that one. All our units are 410a and I'm sticking with that as long as I can.

Its a replacement for R22, 410a is going away also.

[Tom M King]

I stocked up back when I knew prices on everything would go crazy when it was $138 a can. I should be good as long as the equipment here lasts, and by then something else will be out. I don't work on anyone else's stuff.