A/C new install

[Ronmar]

Would you agree that a TXV works much better than an AXV? There is a plug on the bottom of the block opposite the control diaphragm. Air out should be at least as low as 40° and maybe as low as 30° in my view. My car is 41° my M35 was 28°, all with 134A

A TXV might have a slight edge in a wildly varying environment, but the AXV is simpler/more robust, not orientation sensitive and should get you acceptable performance. Again, if you are rolling temps below 32F you risk evap freezups. 35-40f outlet air should do a good job for you if all the air is being processed. I would look a little closer at that plug. Do you have a manufacturer/model number for the AXV, a manufacturers spec sheet should show you where the adjustment is. The caution here is you need its flow/pressure set low enough that all the refrigerant is allowed to completely flash to gas as you don't want liquid refrigerant making it back to the compressor suction...

 

[m-35tom]

It uses a 540031 AXV which is common. The high side is normal at 220 psi on a 90 ° day but the suction is 25 psi which is just below the range it should be in. I will explore adjusting it, the bottom is hard to access but seems to have 2 flat sides, 10mm. I assume back it out so the metering ball can drop more easily.

edit: turning it in 3 1/2 turns dropped temp from 60 to 50 Tomorrow or wed I will put new valve in and inspect old one. Low pressure dropped from 25 to 15, even worse!!

 

[m-35tom]

Installed new genuine AXV, problem is worse. Ambient 90, high side 220, low side 15, evap air 60. At high idle.

 

[Ronmar]

ok, I missed your edit above. How did you get to the 3 1/2 turns, all at once or in slow little steps Monitoring pressure and temp?

does your accumulator have a site-glass on it? One thing that could be happening is that you are indeed low on refrigerant and turning up the AXV or putting in another that is flowing better, increases the flow to the point that you are expending all the liquid coolant In the accumulator And do not have enough flow to maintain low-side pressure... A site glass on the accumulator would be handy in determining this...

 

[m-35tom]

Well kinda. The cap IS the adjusting screw with spring under it. When the suction pressure is low the top diaphragm pushes down on a rod to the ball valve that opens to allow more freon in evap. When pressure is higher the spring adds to that pressure to close the valve and this controls the coil pressure. Backing cap out would allow more freon but only to a point since at low evap pressure the push rod has pushed as far as it will go and backing cap out will do nothing. Moving the spring is only for the balance of pressures when the low side is where the calculation wants it to be. This is why I said this is a very poor choice of valves. It can only allow so much freon in and I think mine needs more in order to cool better. Just a bad design or wrong valve choice by red dot.

So the summary is the diaphragm at the suction side is operating solely based on suction pressure. Low pressure the valve is fully open. High pressure closes ball valve aided by the spring. My pressure is low so AXV is fully open and cannot be adjusted to open more.

 

[m-35tom]

ok, I missed your edit above. How did you get to the 3 1/2 turns, all at once or in slow little steps Monitoring pressure and temp?

does your accumulator have a site-glass on it? One thing that could be happening is that you are indeed low on refrigerant and turning up the AXV or putting in another that is flowing better, increases the flow to the point that you are expending all the liquid coolant In the accumulator And do not have enough flow to maintain low-side pressure... A site glass on the accumulator would be handy in determining this...

Turning screw in closes valve so suction pressure goes down and cooling went down 10°. Yes I have a sight glass but with 134 I don't expect to get rid of bubbles , it is mostly liquid. High side pressure is already on the high side of the chart. I agree it needs more liquid in the evap. Even with the new AXV maybe I should back the adjustment out 1 turn and note pressure change, low side should come up, it is way to low now.

I worked on a car once that had high side way to high but MORE freon actually made it come down, I think the freon was moving through the condenser to fast to be cooled.

 

[m-35tom]

# 26 edited to explain how this AXV works and its short comings.

 

[Ronmar]

# 26 edited to explain how this AXV works and its short comings.

They use AXV’s in a LOT of places, so their shortcomings cannot be that great...

there are two types, one with the spring on the diaphragm side, that was what was confusing me as that spring pressure on that type is increased to open the valve. This type balances the force between diaphragm(fixed preload on diaphragm + pressure applied) and the adjustable spring force to control that ball valve.

turning it in 3 1/2 turns should have lowered the pressure drastically as just about any pressure on the evap outlet side would close the ball.

So what are we missing? unscrewing the spring/opening the valve should raise low side pressure, unless:
1. You don't have any more refrigerant to give. But since you are seeing liquid at the accumulator(And have a very large pressure differential) That is probably not the case...
2. You are exceeding that valves Internal passage/orifice’s ability to flow... When I looked up that p/n yesterday some specced it for 1 1/2 ton and others showed it for 2 1/2 ton. What is your system rated at?

 

[m-35tom]

They use AXV’s in a LOT of places, so their shortcomings cannot be that great...

there are two types, one with the spring on the diaphragm side, that was what was confusing me as that spring pressure on that type is increased to open the valve. This type balances the force between diaphragm(fixed preload on diaphragm + pressure applied) and the adjustable spring force to control that ball valve.

turning it in 3 1/2 turns should have lowered the pressure drastically as just about any pressure on the evap outlet side would close the ball.

So what are we missing? unscrewing the spring/opening the valve should raise low side pressure, unless:
1. You don't have any more refrigerant to give. But since you are seeing liquid at the accumulator(And have a very large pressure differential) That is probably not the case...
2. You are exceeding that valves Internal passage/orifice’s ability to flow... When I looked up that p/n yesterday some specced it for 1 1/2 ton and others showed it for 2 1/2 ton. What is your system rated at?

Yes that is the great question, what is it rated at? No one knows. Evap is rated at 33K BTU by red dot so a 1 1/2 ton valve would give my results??
Yes turning it in did reduce the suction pressure but also reduced the temp by 10°.
Unscrewing the cap will do nothing as the ball valve is already open as far as the push rod can move it, if this is really a 1 1/2 ton valve it needs a longer rod to push the valve open further at low pressure. But how much to change it to 2 1/2 ton? And can the body of the valve flow enough? It looks like it could, just an opinion based on looking at it. Maybe they all have the same components with just different length pushrods.
I need to find the maker of this valve and talk to them.

Do you agree I need more freon fed to the evap? That would increase the pressure and at some point the AXV would actually start closing the ball valve.

 

[Ronmar]

Yes that is the great question, what is it rated at? No one knows. Evap is rated at 33K BTU by red dot so a 1 1/2 ton valve would give my results??
Yes turning it in did reduce the suction pressure but also reduced the temp by 10°.
Unscrewing the cap will do nothing as the ball valve is already open as far as the push rod can move it, if this is really a 1 1/2 ton valve it needs a longer rod to push the valve open further at low pressure. But how much to change it to 2 1/2 ton? And can the body of the valve flow enough? It looks like it could, just an opinion based on looking at it. Maybe they all have the same components with just different length pushrods.
I need to find the maker of this valve and talk to them.

Do you agree I need more freon fed to the evap? That would increase the pressure and at some point the AXV would actually start closing the ball valve.

I think a 1 1/2 and a 2 1/2 Ton valve would use the same diaphragm, rod and spring as they both need to cutoff at Around the same pressure... I think where they are different is that the 2 1/2 ton has a significantly larger (60%) internal orifice And perhaps A little different size valve to flow more refrigerant to achieve that rated outlet pressure At increased flow...

Do I agree you need more refrigerant flow tru the evap? Well yes, since my first response have y0u talked to reddot?

 

[m-35tom]

OK so I need to talk to the maker of the valve to be sure what it is. As you saw, looking the numbers up on the net gives no reliable result and red dot says it takes a 2 ton valve even while they rate the unit at 2 1/2. Thanks. Side note it seems like a few others have been disappointed at the cooling capacity and my view of surplus items is that they just as likely have a defect. Maybe these units were made with the wrong parts and then scrapped. Opposition to that is that each of these valves uses different combinations of fitting sizes so this is the only one I could find that has the correct sizes.

 

[m-35tom]

OK, I have an idea. The valve is probably a 2 ton so 24K btu. MEI lists a valve that is 2 1/2 ton, so 30K btu. problem is it has wrong fitting sizes. So I am going to buy the 2 1/2 ton valve and change my block to use the parts from it, then I will have a 2 1/2 ton valve!! Yes there is a possibility of some roadblocks in parts not fitting but even if I need to make a new block it is not that hard to do. If successful I can then supply upgrades for gen2 units. Maybe.

 

[Ronmar]

OK, I have an idea. The valve is probably a 2 ton so 24K btu. MEI lists a valve that is 2 1/2 ton, so 30K btu. problem is it has wrong fitting sizes. So I am going to buy the 2 1/2 ton valve and change my block to use the parts from it, then I will have a 2 1/2 ton valve!! Yes there is a possibility of some roadblocks in parts not fitting but even if I need to make a new block it is not that hard to do. If successful I can then supply upgrades for gen2 units. Maybe.

The stumbling block, pardon the pun, may be the block itself as that most likley has the machined passage/orifice that controls the overall flow rate. So the guts may swap, but If you are using the original valve block, you are stuck with the same machined passages. I would compare the passage immediately above the ball valve, With that passage on the new valve. I bet its bigger...

Since you have an extra valve you may also be able to open up(drill) that passage above the valve ball to increase the flow of one of yours...

 

[m-35tom]

The stumbling block, pardon the pun, may be the block itself as that most likley has the machined passage/orifice that controls the overall flow rate. So the guts may swap, but If you are using the original valve block, you are stuck with the same machined passages. I would compare the passage immediately above the ball valve, With that passage on the new valve. I bet its bigger...

Since you have an extra valve you may also be able to open up(drill) that passage above the valve ball to increase the flow of one of yours...

Yes, I assumed that the block itself would have larger passages, bigger ball and ball holder etc. I cam just machine the original block to match. Or just make a new block with the correct line sizes. I found 2 for $10 each so got both.

 

[Ronmar]

Cool, let us know how it works out.

Also doing a bit of study on this type of AXV it also employs some properties of a TXV which is probably why it is used in so many places. Pressure buildup On the outlet of the evap applied to the diaphragm, relaxes pressure on the rod allowing the ball to close on its valve seat to regulate the pressure on the evap outlet.

The pusher section of the diaphragm Assembly and the pushrod are also subject to thermal expansion and contraction so the colder it gets, the shorter that assembly gets making it easier to close the ball with slightly less pressure(and refrigerant flow).

The opposite is true if the pusher and rod assembly are warmer, they are longer which pushes the valve farther open and it takes just a little bit more pressure(and flow) on the evap outlet to close the ball...