Carrier A/C, Again!

[hrdwrkingacguy]

Re: Carrier A/C, Again!

The valve will try to maintain whatever superheat you set it to...I wouldn't think you even need to adjust it...What you are trying to accomplish is around 12 degrees superheat(68-70# suction pressure with a 50 - 52 degee suction line temperature) and then have 8 to 10 degrees subcooling...If the valve is set to 12 degrees(which should be what it starts at) and you have 4 degrees of subcooling you are undercharged...If you have 12 degrees of superheat and 25 degrees of subcooling you are overcharged...

The main question in any refrigerant diagnosis is "Where is the liquid"

Since you superheat vapor and subcool liquid, high superheat means high vapor...And vapor doesn't move heat, liquid does...Less superheat means you are flooding back liquid to the compressor...So target superheat is 10-12 degrees at the indoor coil...

Since you subcool liquid target subcooling is around 9 degrees...High subcooling means high liquid level in the condenser, and since liquid in the condenser already gave up its heat, excessive liquid is useless and limits space in the coil for it to do work...

Essentially you are looking for just enough subcooling to keep a solid column of liquid in the liquid line, and enough superheat to ensure that the compressor is seeing only vapor in the suction line...

Gawd where is a dry erase board when I need one...

PS by way of setting superheat and subcooling you are controling where the state change occurs at...to much superheat and the state change happens to early and since vapor doesn't move heat you lose capacity...To much subcooling and the state change occurs to early and you stack up liquid in the condenser and lose capacity...

 

[Nandy]

Re: Carrier A/C, Again!

That valve is not going to work. I see no way to move the 5/8 female compression from the old valve to the new valve. I had not taken the system apart so all I did was put the evap cover back and flip the on button for the ac. Maybe I told them something wrong when they started asking me about line size, I did offer the old valve number but it was declined. Wonder if that would have help.

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

Sure it will...Cut off the flared part off the indoor coil and slip the valve on...It doesn't have to be a flared connection...As far as the old valve # they aren't a danfoss dealer so they can't look it up...

Post a pic of the old txv in the unit so I can see all the lines and I can give you options...

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

Sorry to double post...I looked that coil m# up and I believe it has a 3/8" on one side and a 5/8" on the other...They type of connection and honestly even the size doesn't really matter(as long as you don't go smaller then the valve you can go larger)...if you have to cut off the flare and there is a few inches of copper pipe left, you can get reducing fittings or even a piece of copper that fits the valve and make it work(Think insert slot A into tab B) however you have to...

 

[Nandy]

Re: Carrier A/C, Again!

I chicken out and decided to wait to see if the local store has the connector I need. I rather do that than take the chance to mess us and then not being able to use the old valve. If you look at the ebay link that is the exact same valve. I did move the valve outside of the evap case and im getting 14 superheat but it's been cold today. We shall see what happens between now and next weekend when I will try this again.
Thanks!

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

That is the nature of restrictions...They cool to a certain temperature, but above that they can't deliver enough refrigerant...14 is borderline...See what happens when the temp goes up 15 degrees...I bet its 25...

 

[Nandy]

Re: Carrier A/C, Again!

Readings from today:
Liquid line 250 psi
Liquid line 98 deg (next to service port)
Suc line 72 psi
Suc line 57 deg (next to service port)
Outside temp 84 (at 5:30, about 90 min past the hotter time of the day)
Inside temp 77 per thermostat (digital thermometer shows 73, thermostat set for 74)
Return upstairs is 70.
Registers is 55.

Superheat is 15.
Subcooling is 18.

I will rather wait until a hotter day. I did expect some changes, that valve bulb was not only sitting inside of the evaporator case but directly in the flow of cold air, the insulation around it was laughable...

Here is the picture of the valve, I had taken the bulb off already but it was where the grey tape pieces are. The insulation was a 1/6 inch foam piece wrapped around it but not tight. The edges to the sides were wide open to cold air to come in and out....

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

15 degree air split and 18 degrees subcooling = that units going to struggle as it gets hotter...

That picture is like worst case for installing an aftermarket valve...I think there is an adapter to turn the flared distributor into a 1/2" pipe...

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!



Is there a solder joint where the arrow is? like the flare connection is soldered onto the distributor??? If so you can loosen this up with heat and braze the valve there...

 

[Nandy]

Re: Carrier A/C, Again!

I will have to go up there and check again. I ran by the local dealer but they did not had any the connectors I needed. There is another place i will try tomorrow.
I know the number is not good but the change at least reinforces the theory that the valve is not opening enough and this replacement valve might do the trick. Today we were in the lower 90's and the ac is keeping the temperature a lot better that it had before. Still, the valve needs to be changed....

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

I am doubtful you will find that fitting...The only way I(I think) to do it is from a ICP dealer...There may be a something I can do from here...I will check tomorrow...If I can get the piston holder fitting from Sigler, I will take it to ARS and have them send it, and I will take care of it...They should still have the info where they sent the txv...

PS. Are you running it with the txv sensing bulb removed? or attached outside of the coil to the suction line???

 

[Nandy]

Re: Carrier A/C, Again!

The sensing bulb it is about 2 to 3 inches outside of the airhandler attached to the suction line. I used the black insulation from the pipe and then added some more to cover it completely. Added some duct tape around it to seal it as much as I could. I appreciate anythig that you can do. I hate to give you more work than what you already have tho...

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

I just realized something...Do you still have your old coil? The piston holder has the same size fitting on it in the picture...I think you can use that if you still have it...

 

[Nandy]

Re: Carrier A/C, Again!

Sorry for the late response, you are right, it does fit. It does have a strainer in it and I dont see why to remove it.

You can see how it looks now. My plan for the equalizer line will be to braze it to the current equalizer line but just close to the connector. If you look at it, the old line is about 5/16 close to the connector so I can use that. If I find a problem with that then I will use that straight copper adapter, make a hole in it, clean it, braze it to the new equalizer line then cut the suction line where the old 3/8 connector is and use the coupler with the already attached new equalizer line. That way I have no worries about messing the suction line while trying to burn a hole in it. Im not too confident on doing the hole with the torch. That way not only I keep myself from burning thru the pipe I also keep any debris out since I will do the hole on the unattached connector.
I guess Im ready for Saturday, now, I need to finish the blazer ac, got the parts yesterday...

 

[Nandy]

Re: Carrier A/C, Again!

Interesting observation today at the suction line...
78 psi =46 deg
55 deg
9 subcooling
95 deg day, super sunny all day...
House is 77 deg.
Usualy I would have been in the 80's inside the house. Since I am in the other side of superheat where the valve is opening too much???!!!

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

You aren't listing high side pressure, so its hard to say whats going on...Is 90 degree's on the high end of the scale for your area or is it cooler then normal right now?

A unit with a txv should be able to respond to temperature...Think if it like a curve on a graph...the Right side is lets say 80 degrees, the temperature goes up to 105 then back down to 80 over the course of 18 hours...A working refrigeration system will allow a larger volume of refrigerant through the valve all the way up to 105(or whatever the max temperature is) Then as it cools down the volume will go back down...

Your system has, instead of a round curve a square where there is a temperature that it stops increasing the volume of refrigerant(That's the restriction) so when the outdoor temp is on either side of this max it works, but above that the unit doesn't respond...

Another example of where I need a dry erase board...

 

[Nandy]

Re: Carrier A/C, Again!

I was in a hurry to head to work so I only got one reading. Might try both sides tomorrow depending on how my day works.
I think I understand the concept, dont worry too much about not having a board. Correct me if I am wrong.
1. A system using a piston (like my old evap) can only provide a steady flow of refrigerant to the evap coil. As the temperature rises the piston being static cannot increase the flow of refrigerant on by itself. This affect the efficiency of the system as the superheat of the system can be lets say 7 at 70 deg but 30 at 100 deg (just numbers there).
2. With a txv the flow of refrigerant into the evaporator coil can be changed. The valve drives its orifice larger or smaller depending on the temperature of the suction line (and other factors) attempting to keep the determined ideal superheat number.
3. If the superheat number is high then you have what I been having, a system that is not delivering enough refrigerant to the evap to be balanced. If you get low numbers, like I did today, it probably means the valve has open beyond the ideal superheat and it is delivering to much refrigerant for the system to be balanced. When I say balanced i mean that point when you are delivering the maximum amount of liquid refrigerant to the evaporator coil and it gets evaporated by the evaporator load and (ideally, I think) there is no liquid refrigerant at the other end where it goes into the suction line.
4. So that leads me to believe my valve just opened up too much today, probably influenced by the 115+ deg heat in the attic and maybe being not ideally insulated by me.

Would that sounds about right?

PS - July tends to be the hottest month. The max is 103 but it is generally in the uper 80's lower 90's. so I can say this is probably very close to the hottest days we will have. Im sure there will be hotter but generally not in the 100's.

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

Lengthy rebuttal incoming! but it will have to wait till after harry potter...

 

[Nandy]

Re: Carrier A/C, Again!

ok, dont forget your blackboard!!! Keep in mind that that was a simplistic way of explain how the system works. Looking forward for your reply.

 

[hrdwrkingacguy]

Re: Carrier A/C, Again!

In a fixed orifice system(ie cap tube,flowrator,piston,stuck txv) superheat, and subcooling is related more to load and compressor compression ratio...Head pressure in a 10 seer or less system is around the ambient + 20ish degrees...

So in your system @ 90 degrees + 25 = 225# and you "Should" have a 105 degree liquid line...with a 70# suction pressure you have a compression ratio of ((225+14.7)=239.7/(70+14.7)=84.7 = 2.82 to 1...Since the Indoor temperature "generally" stays the same as the head goes up due to the ambient going up to lets say 100 degrees you would have...

100+25=281# head pressure and a suction of 70# = 281+14.7 / 70 + 14.7 = 3.49 to 1

This increase in compression ratio increases the flow rate of the refrigerant driving more liquid through the metering device...

So the long and short of it is in a fixed system superheat and subcooling go down when the outdoor load increases the compression ratio...So at 70 degrees outside and 75 inside you may have a superheat of 40 degrees...when its 115 out you will have 0 superheat or really close to 0...

My feeling is you have essentially a "fixed" system when the txv reaches the end of its "stroke" and then pumping velocity takes over and that in a nutshell is why you see random "ok'ness" out of your system...

PS for the sake of the lost compression ratio is PSIA(pounds absolute, instead of gauge) head pressure \ PSIA suction pressure...PSIA is gauge pressure + 14.7#