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Old 08-05-2022, 08:41 AM   #1
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Evans-Tempcon Dash Air - Expansion Valve orientation

Our Ď02 coach has the above Evans ďair handler/coil boxĒ section in the dash firewall for providing the limited but somewhat useful climate control functions for the front of the coach.

After a compressor failure last year (electrical short against the drive pulley), and subsequent finding the OEM compressor had an inherent leak flaw that couldnít be seen without removing the compressor - I still havenít been satisfied with how the A/C system performed.

The water control valve for the heater section has been replaced and confirmed to be closed.
But the expansion valve is acting wonky as it tends to hunt more than I would expect. It is well wrapped with cork (Prestite) tape.

Iíve never really liked the set-up that was used by the coach builders when they ordered their chassis. This one is on a Workhorse chassis, and Workhorse shipped the chassis with the compressor, hot gas line to the condenser coil, receiver/drier, and liquid line with a one time valve that would release pre-charged refrigerant when connected.
Evans would then provide a liquid line connected to the expansion valve where the expansion valve was connected to the cooling (DX) coil.
And then Workhorse would provide the suction line back to the compressor which included a ďking valveĒ aka ďservice valveĒ that connected to the suction port of the expansion valve.



In looking to replace the expansion valve, and because the king or service valve really serves no purpose, I plan to remove it.

All the above to get to my dilemma - both connections between the expansion valve to the cooling coil are a #8 o-ring type - which means the expansion valve can be put on either way. Either way in that the refrigerant flow thru the coil can be such that the coldest refrigerant can meet the coldest air, or the coldest refrigerant can meet the warmest air.

In typical A/C systems - you want the coldest air to see the coldest refrigerant. And with the expansion valve hunting, Iím suspect that it may have been installed backwards from the factory.
Itís hard to see inside of the coil box to tell how the cooling coil is circuited. It does appear the coil lays flat, and that one of the expansion valve tubes is higher up on the coil slab than the other - but itís just hard to tell because I canít see in there well enough.
From a refrigerant flow point of view, one would want the expansion valve to feed low, and allow the warm vapor to exit the coil high - but doing that puts the coldest refrigerant against the warmest air.

Just wanting others thoughts as I go to open my system up to replace the expansion valve and remove the king/service valve (note, some new hose fittings have been located and will be implemented to retain both the suction service and clutch cycling switch ports).
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Old 08-05-2022, 09:42 AM   #2
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I don't know.. I have replaced both type of expansion valve.. I can't recall their proper names.. but the traditional one and block type one.. and they only go one way.. and I can tell you they are the cheapest part.. or one of the cheapest parts.. and for some reason I don't understand.. a/c tech always over look.. that is only my experience.. your is right where you can get at it.. mine was inside under dash.. many directions say they can have a screen that gets plugged up.. but when I change them out.. never can fine a screen.. so I always just change it.. one thing I can tell you.. the traditional ones under dash are a bare to get at.. and the block type.. like what you have.. are a pain yo get off.. they look simple.. but they are really on there..
Good luck and keep us posted
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Old 08-05-2022, 10:04 AM   #3
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Maybe a source of parts and information that you might need.

Texas Truck A/C
4701 Cleveland Road, Dallas, Texas 75241

Standard Hours:
8 A.M. - 5 P.M.

Office: 972.289.2010
Toll free: 866.481.9654
Fax: 972.289.7772

Shop manager: Marty
******************************
Fast Hose
2624 Industrial Lane
Garland, TX. 75041

972-271-8591

I have used both companies and they do excellent work.
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Old 08-05-2022, 03:31 PM   #4
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Quote:
Originally Posted by donr103 View Post
I don't know.. I have replaced both type of expansion valve.. I can't recall their proper names.. but the traditional one and block type one.. and they only go one way.. and I can tell you they are the cheapest part.. or one of the cheapest parts.. and for some reason I don't understand.. a/c tech always over look.. that is only my experience.. your is right where you can get at it.. mine was inside under dash.. many directions say they can have a screen that gets plugged up.. but when I change them out.. never can fine a screen.. so I always just change it.. one thing I can tell you.. the traditional ones under dash are a bare to get at.. and the block type.. like what you have.. are a pain yo get off.. they look simple.. but they are really on there..
Good luck and keep us posted
Thanks Donr103!

I donít foresee any issue with getting this TEV off. All 4 port connections are the o-ring type with male swivel nuts - and like you said, are more easily accessible than most (that Iíve seen in automotive).

And usually they can only go one way - but there is nothing on this system that determines a ďcorrectĒ way. Both ports on the evaporator are the same size - and there is nothing that would prevent someone who doesnít know better to put the liquid pass thru port on the wrong evaporator port, which then puts the suction pass thru port on the wrong evaporator port.

The way this evaporator appears to be made (for what I can see) and the way the TEV was assembled to it (I assume) from the factory - the suction port (which is the warmest refrigerant) is on the gravity bottom of the evaporator.
That is poor design.
Refrigerant flow thru an evaporator should be bottom to top to take advantage of gravity (the only time this is hard to do is in a down flow air handler) to insure all the liquid refrigerant has boiled away and is superheated before leaving the evaporator.

About the only place Iíve seen screens in a TEV is when it is used in residential or commercial HVAC/refrigeration - and they typically donít use block type TEVís. Iíve never seen a screen in a block type TEV, but then I have less experience with them in MVAC.
But trash in any TEV can be problematic, and block valves tend to be a bit more sensitive to trash due to how they work (functionally they do the same thing, but they are mechanically different). This is why I suspect youíve never seen a screen with a block valve.


Quote:
Originally Posted by rvbiker45 View Post
Maybe a source of parts and information that you might need.

Texas Truck A/C
4701 Cleveland Road, Dallas, Texas 75241

Standard Hours:
8 A.M. - 5 P.M.

Office: 972.289.2010
Toll free: 866.481.9654
Fax: 972.289.7772

Shop manager: Marty
******************************
Fast Hose
2624 Industrial Lane
Garland, TX. 75041

972-271-8591

I have used both companies and they do excellent work.

And Thanks to you as well rvgiker45!

Very familiar with HoseFast in Garland - worked in a building across the street from them Ď78-Ď80 before our company moved.

Iím not trying to build hoses - which is what HoseFast does (recently had them build replacement hydraulic hoses for our coach levelers and need to get some more made).
Iíll call TexasTruckAC and see if they can confirm the correct orientation of the expansion valve on our coach.

I guess in the back of my mind, Evans Tempcon didnít understand the thermodynamic of warmest air sees the warmest refrigerant, or might possibly allowed for it in how the suction line of the evaporator was circuited - it just doesnít look like it for what I can see -

I can change it when installing the new TEV, but then if Iím wrong, it means recovering the refrigerant and flipping the TEV over then recharging.
I would rather only go thru this once, and hopefully get it right.
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Old 08-05-2022, 06:10 PM   #5
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Quote:
Originally Posted by MrMark52 View Post
...I would rather only go thru this once, and hopefully get it right.
"An' here I sit so patiently
Waiting to find out what price
You have to pay to get out of
Going through all these things twice"
- unnamed Nobel laureate

Could have been written about RVing in general.
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Old 08-05-2022, 08:45 PM   #6
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The ones I have changed the center through bolt is off set.. if your is that easy to confuse.. think about the poor general line labor.. that gets about 10 seconds to get on.. and do that for 12 hours.. you are bound.. no perfect you are.. to get reversed.. good luck.. I see only 25% chance you will get it right.. 1st time.. you could.. if you get it correct.. it could take 4 times.. if you Mark it.. and keep perfect records .. well cheer up.. when you get it right.. that will be the last time.. hopefully 1st time..
Good luck and keep us posted
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Old 08-06-2022, 06:31 AM   #7
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Please keep us updated on how this goes, and how it performs, I will probably be redoing pars of my air conditioner system this winter and may want to consider this.
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Old 08-06-2022, 07:57 AM   #8
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Please keep us updated on how this goes, and how it performs, I will probably be redoing pars of my air conditioner system this winter and may want to consider this.
Will do!

FWIW - I would expect most systems that use a block TEV are designed such that TEV installation is straight forward and will only go in one way (whether the system was properly designed or not). The few automobiles that Iíve worked on the A/C system were made this way - but the MoHoís Iíve laid eyes on donít seem to follow the same rules.
The block TEV on our previous coach had the same port sizes on the evaporator side too - but the hard lines inside the air box for the liquid and suction side of the valve dictated TEV orientation (I had to replace the combo evap/heater core due to a leak).

This coach, the liquid and suction lines from the filter/drier or return to the compressor are flexible and can be easily moved to meet up with the TEV, regardless of itís installed orientation - and since both evaporator connections are the same size, the TEV can then be installed ďforwards or backwardsĒ (so to speak).
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Old 08-06-2022, 03:15 PM   #9
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Another FWIW - inlet filter screens for TEV’s will always be on the liquid port - either in the TEV or somehow in the liquid line.

If you look at one of the old in-line orifice designs (not a TEV) - you’ll see a screen ahead of the orifice to protect it from clogging with trash (that shouldn’t be there). TEV’s have a filter screen of a similar mesh to protect the internal working parts (and the compressor somewhat).
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Old 08-06-2022, 05:47 PM   #10
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I found a 76 page document by Evans-Tempcon that says they furnished 4 different combo evaporators/hot water heat coils for use in MoHoís, with a picture of each.
Only 1 of the four have refrigerant and water connection ports that look anything like what I have.

Assuming their statement is true - then itís a poorly designed evaporator. From the picture provided in the document, as best I can tell, the warmest air meets the coldest refrigerant. And, which also means they donít take advantage of gravity to insure all the liquid refrigerant has been vaporized and superheated before passing out of the TEV on its way to the evaporator. Fortunately, itís a single circuit 2 row evaporator which is fed from the face bottom, makes 3 passes on the face row before turning to the 2nd row and making 10 passes before returning to the face row and making another 8 passes before turning and going into the suction port of the TEV.

At least thatís how it looks in the picture - from what I can see of what would be of the suction port on our coach, that line goes in a different direction - so circuiting could be slightly different. And if Iím guessing right, it would be for the better.

Still looking for anyones thoughts/comments as well
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Old 08-07-2022, 04:41 PM   #11
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Todays update -

I thought due to the fairly easy location of the TEV that it would take me an hour or so to unbolt the TEV, disconnect the liquid and suction lines (I had already recovered the refrigerant), cut the suction line, install the new hose adapters in the suction line, install the new TEV, and hook up the suction and liquid lines.

I was wrong. I went to disconnect the evaporator from the expansion valve first. Couldn’t do it with a 14” crescent on the TEV and 12” crescent on either of the evaporator swivel nuts.
Went and bought line wrenches to minimize the potential I would strip the swivel nut hex’s.
Still no budge.

Squirted a 50/50 mixture of acetone and transmission fluid on all 4 ports, put my tools away, and went to work on other projects.

I did get a slightly better look inside the coil box so as to see the coil circuiting. Apparently the Evans-Tempcon document mention previous wasn’t totally correct. Due to what it is looking like now - it’s looking more like the original TEV was installed backwards.
Sadly, I can’t do anything about the circuiting of the coil, but I can insure that the liquid port feeds the face 1st row of the coil (which is the gravity bottom of the coil in terms of refrigerant flow) and the suction port of the TEV is the 2nd coil row - which better insures refrigerant superheating - meaning no liquid returning back to the compressor.
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Old 08-08-2022, 05:33 PM   #12
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It looks like you are experiencing a couple of levels of stupid. 1: Those 4 port TEVs are mostly junk. I installed in dash air in my younger years and we had to replace about 10% of those 4 port valves, under warranty. 2: They don't need to be tightened near as tight as you are experiencing. They use tube "O" ring fittings. It's a shame that Evans-Tempcon even exists. They don't have the quality or sizing that's needed in a RV. The Denso units do a better job.

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Old 08-08-2022, 07:55 PM   #13
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If you should bugger the coil for the unit and want to recover it, give Forney Radiator a call.

Forney Radiator
103 E. Broad St.
Forney, TX. 75126

972-564-3431

8-1730 M-F

They do good work and are reasonable. I have used them.
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Old 08-08-2022, 08:50 PM   #14
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Quote:
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It looks like you are experiencing a couple of levels of stupid. 1: Those 4 port TEVs are mostly junk. I installed in dash air in my younger years and we had to replace about 10% of those 4 port valves, under warranty. 2: They don't need to be tightened near as tight as you are experiencing. They use tube "O" ring fittings. It's a shame that Evans-Tempcon even exists. They don't have the quality or sizing that's needed in a RV. The Denso units do a better job.

Richard
As for stupid #1: My experience with these block valves is limited mostly to vehicles Iíve owned over the past 50 years. I canít remember having to have replaced a single one, but cleaned out my share of orifice tubes and every day expansion valve screens.

But you likely saw more than I did.

Stupid #2: Your right - o-ring swivel joint connections only need to be snugged. What I donít know is if there might be some aluminum oxidation against the steel threads that might have occurred.
Best I can tell, this coach has only lived in North Texas so road salt isnít at play here, even if it would have an i pact.

And Stupid #3 (which you didnít mention, but Iím adding) - the TEV appears to have been installed backwards because Evans-Tempcon didnít use different size swivel nuts on the evaporator (like #6 liquid in, #8 liquid out, #10 vapor in, #10 vapor out - you canít install that backwards which insures only refrigerant vapor reaches the suction line heading back to the compressor).
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