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Evap to Compressor Matching - and my Project

vtwinwilly on Tue April 15, 2008 11:07 AM User is offline

Year: 1993
Make: Holiday Rambler
Model: Nvigator
Engine Size: 8.3
Refrigerant Type: going to 134a
Ambient Temp: 90
Pressure Low: ?
Pressure High: ?
Country of Origin: United States

I'm a newbie so you guys go easy on me.

Question: How can I verify that my AC compressor is properly matched to my Evap Coil?

My Project: I recently purchased a 1993 Holiday Rambler diesel pusher. The dash air does not blow cold, and does not blow very hard, even on high. The previous owner had the unit since 1995, and said the dash air never did blow very cold. He said at its best, it would blow air at about 60 degrees... cool, but never cold.

I got to looking at it, and the high side hose was loose at the compressor, and the system was/is completely devoid of any freon. I want to resurrect this A/C system, and get the dash air working the way it should have all along. I'm hoping AMA can help me with this project.

Here's what I'm thinking I want to do (looking for guidance here):

1) Make sure I have a properly matched Evap to compressor combination. (again... how do I do this. My thought is it was never properly matched)

2) Purchase DIY starter kit and DIY Flush kit

3) Flush anything that is not to be replaced.

4) Switch from R-12 to R-134a

5) Go to a larger compressor/evap if necessary. This includes a blower that can move more air.

6) Replace the condenser coil to parallel flow high efficiency model.

7) Replace both condenser Coil fans. 2 - 16" fans. (both are frozen and will not spin)

7) Replace Drier and expansion valve.

SOME FYI DETAILS:

1) Current compressor: Seltec DKS-15CH (I'm pretty sure the seals are bad and am willing to, and expect to replace this)
2) Power - Cummins 8.3 diesel 300hp
3) Current condenser Coil is 18"h x 34"w, copper coil and fin. (I can't find a parallel flow condenser this big... any ideas?)
4) Condenser coil is side mounted, in the rear of the coach and dependent on the 2 fans for cooling.
5) There is at least 40' of A/C line from the compressor (in the back) to the dash evap/blower unit (in the front).

So AMA... what do we need to do to get this project started?

Sorry for the long post. just trying to provide as much info as possible.

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

CorvairGeek on Tue April 15, 2008 11:17 AM User is offline

Is there any mfg information on the evaporator case, most likely names are Evans or Acme (no, that's not a joke)?

-------------------------
Jerry

vtwinwilly on Tue April 15, 2008 11:24 AM User is offline

Jerry,

Thanks for your quick response.

I haven't torn into the evap/blower unit yet, but will take a look and see if I can get you a mfg and part number.

Bill B.


-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

bohica2xo on Tue April 15, 2008 12:06 PM User is offline

Oh boy, "afterthought air". I see all kinds of marginal installs from coachbuilders. Rarely the same from unit to unit...


That little 9 cubic inch compressor can only do so much. A recurring disaster on diesel installs is badly underdriven compressors. That compressor needs to spin 3500 rpm to get near full capacity, and has a maximum continous speed of 6000 rpm. Have a close look at your drive pulley ratios. Calculate the compressor speed at idle & govenor maximum - and post your results.

How much of your 40 feet of plumbing is hose?

B.


-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

vtwinwilly on Tue April 15, 2008 3:27 PM User is offline

B.

I will check the circumference of the pullies and get an answer back to you today (probably this evening).

Like you, I've experienced many RV A/C units that don't perform well. It's hard for me to understand... after all, the A/C on my toad (2003 Saturn VUE) will blow you out of the car and freeze your nose off at the same time. Anyway...

To the best of my knowledge, the 40 ft of plumbing is all hose. I don't know this for sure as the lines run into the deep abyss between the frame rails. This area is enclosed to provide better aesthetics from the basement area, but it makes servicing anything inside the frame rails a nightmare. Everything I can see outside the frame rails is all hose. I am willing and ready to run new lines if that's what it takes.

Stand by for the additional info.

Thanks,

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

Edited: Tue April 15, 2008 at 3:27 PM by vtwinwilly

vtwinwilly on Tue April 15, 2008 9:10 PM User is offline

B.

The circumference of the drive pulley is 22.375". the circumference of the compressor pulley is 17.125 ". If I do my math right I get...

22.375 / 17.125 = 1.306 or the compressor pulley turns 1.306 times for every revolution of the drive pulley.

Being a diesel, it idles at 500 rpm, I've never seen the tach go over 2600 rpm, and at 70mph it's turning about 1800 rpm.

Based on this, I'd say that even at 70mph the compressor is only turning 2350 rpms ( 1800 * 1.306 ). No wonder the thing has never cooled so well.

I checked as best I could. It appears that all the plumbing is rubber hose. I'm sure I'm suffering some additional preasure loss here.


Jerry,

I could not find a mfg or Part number on the evap assembly. I looked everywhere I could get to. even disassembled part of the dash. There may be something on the inside of the case, but I haven't had a chance to take it appart yet. I will call Holiday Rambler tomorrow. Often if I give them a VIN they can tell me what parts went into it.

Thank both you guys for your help so far.

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

bohica2xo on Tue April 15, 2008 11:38 PM User is offline

Bill:

Not a big surprise, but it does explain the lackluster performance. The output from that compressor with the cummins on the govenor @ 2800 is not yet at full capacity. I bet idle cooling is uh, minimal. A 2.2:1 overdrive would have been a better choice.

Changing the drive could be a huge pain in the backside. So would going to a much larger compressor, as some makes do. It depends on how much fabricating you are up for. Otherwise, just clean the system up & get all you can - with the knowledge that you are limited by compressor volume.

Don't worry about the 40 feet of rubber hose, unless it is in bad shape visiually. It is an indicator of how much thought went into the system design however. The only down side to hose is that the system will get wet faster than an automotive system with 4 feet of rubber. All hose passes moisture, regardless of pressure. The manufacturers rate the permeability by the foot, so 10x as much hose passes more water. Plan on a new dryer every 3 to 5 years as a PM item.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

CorvairGeek on Wed April 16, 2008 2:39 AM User is offline

I was curious on the mfg for the heater core/evap case because I thought the air flow on the Evans and Acme systems was pretty good by that era. I wondered if the fan had full voltage, air flow blockage inside the case, leaky duct work, bad installation, or some other brand or a HR home grown design. I'm stunned (but not really knowing RVs) to find out they used a 9 cubic inch compressor when I've got a Sanden SD7H15 (15 cubic inch) on a gas class A.

-------------------------
Jerry

bohica2xo on Wed April 16, 2008 2:48 AM User is offline

Jerry:

You have a 9.5 cubic inch Sanden. 154.9 cc's per revolution. I would be thrilled if Sanden made a 15 cid unit in that case size!

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Wed April 16, 2008 at 2:49 AM by bohica2xo

CorvairGeek on Wed April 16, 2008 3:10 AM User is offline

I appreciate that. I thought that number was awfully high, but I think that is what Ford claims in the F53 shop manual, or I ran across it some where else (old age The way it loads a 460, I've always been suspect of the efficiency claims compared to an old A6, especially now finding out it is smaller than an A6. It does cool very well (tvx).

-------------------------
Jerry

vtwinwilly on Wed April 16, 2008 11:01 AM User is offline

Thanks guys,

I'll have to start researching my solution.

Again, if I do my math right, to get the compressor to spin at the desired rpm, I would need a drive pulley with a circumference of about 37 inches (17.125 * 2.2). This would be a 12 inch diameter pulley... hmmm, that might be doable. Only other choice would be to do as you say and insert another set of pulleys and belts that creates an overdrive.

At this point it looks like the current installed system has some fundamental design problems (I think we all knew this), so my question to the collective is... if you were to design a high quality well functioning system to install in my RV, what would you do?

I plan to keep this RV for several years. I don't want to patch the A/C and make it work "OK" . I want to fix it right, and have a system that works, and works well. I don't necessarily want to replace all the components of the system, but I'm willing to if that's what it takes.

Thanks again,

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

bohica2xo on Wed April 16, 2008 12:35 PM User is offline

Jerry:

Your 460 Ford probably has the same 1.3:1 drive - but your gas engine spins up a lot higher, so you get good performance.

Bill:

You have a few options, but it depends on your fabrication capacity, and parts availability.

There may be a large crank pulley for that Cummins, I know there are for the CAT. Obviously your biggest hurdle is the output vs speed issue, and this would help the most.

I believe there is a 210 cc/rev Seltec (21HX) that might be retrofitted, depends on your mount now. A picture of your current install might help here. Vee belts? Swing mount with a dedicated belt? Running with other accesories? You get the idea.

The final (and somewhat over the top) solution would be to start from scratch. I just finished a pusher coach that was fitted with a TM31 compressor (310 cc/rev) that cooled very well. The compressor drive was pure Rube Goldberg, but the drive ratio was 1.8:1. They were running two evaporator assemblies with TXV's. The bad news is that compressor is about 800 bucks wholesale, and it would be a big job to start over.

I think you solution probably lies someplace between the extremes of "as is" & "new system". A trip to the Cummins dealer might be a good place to start.

As for the poor airflow through the current evaporator, you need to pull it apart. There may be 5 pounds of dog hair in it, or a missing seal that allows the air to circulate inside. Or the fan motor may be crap. I once found a 24v fan motor installed on a 12v vehicle, had poor airflow... You just don't know until you look.

B.



-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

vtwinwilly on Wed April 16, 2008 2:58 PM User is offline

B.

Sounds like I need to tear into the evap assembly and see what's there.

Also, I looked at the Worldaire site and they list the TM21HX for r134a only... which brings up another point. I was planning to switch to r134a, but elsewhere on this site "Tim" instructed someone to get Section 609 certified, and stick with r12. This would prevent me from having to replace my condenser. Your thoughts?

To answer your question. I can fabricate steel fairly well so long as it doesn't require anything more than a torch, welder, drill press and grinder. I'm sure if my existing bracket won't work for a TM21HX, I could fabricate something that would. Might not be real pretty, but it'd work!

I couldn't find any specs on the TM21HX. Would this also have to spin at 3500 rpm to be effective or could it spin slower and still deliver enough refrigerant to make it effective?

thx

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

bohica2xo on Thu April 17, 2008 4:14 PM User is offline

Bill:

Your best solution would be a better drive, with any compressor. You say this is an 8.3 rated at 300hp? That would make it an ISC. Vee belt drive was behind the damper on that one, is that what you have? I am aways from my library, but if you can narrow down the engine I will see what is available.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

vtwinwilly on Thu April 17, 2008 7:44 PM User is offline

B.

My Cummins is a C8.3, the predecessor to the ISC motor. While they're the same displacement, I'm not sure they share much else.

The serial number of mine is 4482-2641. With this you should be able to identify any parts for it... at least everytime I call Southern Plains for parts they always ask for the serial number.

Below is an a picture of my current installation. Shows the compressor mount and both the pulleys.



Hope this tells you something.

Bill B.

-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

Edited: Thu April 17, 2008 at 7:58 PM by vtwinwilly

oznznut on Thu April 17, 2008 8:56 PM User is offline

How about an A6 with a 5" Pulley? That would give much more compressor capacity, about 12 cubic inches IIRC, and a compressor rpm of 2550 at 1800 engine rpm. More compressor capacity, better speed. Might work.
Dave

bohica2xo on Fri April 18, 2008 3:18 AM User is offline

Oh boy, a secondary drive. You need to have a look at the crankshaft to waterpump ratio before we call that one all bad.

I recall some FL70's with a York mounted in that location with a similar drive arrangement, but all they cooled was a truck cab.

An A6 could be fitted into that bracket, as oznznut just suggested. A V7 Like This could also be mounted with a little creative use of angle iron in that mount. 179 cc/rev, variable displacment. The vee belt pully from the earlier V5 fits on the V7, and it is 5 inches as well.

The TM21 is a "pad mount" like the V7 picture. 13 cubic inches or 210 cc/rev For a good visiual reference of compressor types Look Here

Tim can get you most any of the pictured units at a fair price. There are a few SD7 Sandens that would also drop easily into that bracket...

If you measure the space inside that mounting bracket, you might even be able to drop a TM31 in that space. 313 cc/rev & ignore the drive specs. Not cheap though.

Otherwise a special waterpump accesory drive pulley may be an option - depending on the actual crankshaft drive ratio.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

Edited: Fri April 18, 2008 at 3:34 AM by bohica2xo

vtwinwilly on Fri April 18, 2008 10:49 AM User is offline

When I first looked at the pullies, it appeared that the crank pulley was the same size as the "power take-off" pulley... so let's take another stab at this.

My new calculation has the compressor spinning at 2700 rpm when I'm turning 1800 at the crank or a 1:1.5 ratio.

See the pic below for details.

BTW... the pulley as marked is the water pump (one with the surface rust) I had to replace it a few months ago.




-------------------------
93 - Holiday Rambler Navigator
Project - Fix the Dash Air

Edited: Fri April 18, 2008 at 10:51 AM by vtwinwilly

bohica2xo on Fri April 18, 2008 11:52 AM User is offline

Nice job on the picture Bill!

So, 2700 @ cruise. Better, but idle performance will still be weak. I guess the good news is you don't have an auxiallary crank pulley & a 133 inch belt...

The PTO bearing assembly is used to hang the fan on in medium duty trucks, so it is fairly stout. Since you know the guys at Southern Plains, give them a call @ see what your options are for a larger pulley in that location. Remember to have them look at both Vee belt & Serpentine type pulleys, because A/C compressors are available both ways. You can use any pulley combination that hits 6000 rpm at the govenor speed. Some compressors will even 7000+ rpm in short bursts.

The big reason to look for higher pump speed & output is idle cooling. It sounds like you have a large condensor, so depending on the size of your evaporator you may have a use for a lot more pump capacity. You asked earlier about the 134a switch. I would not have a problem converting this system to 134a, but flushing would be a big job. R12 & the online certificate is easy enough to do. The refrigerant cost vs labor to convert is a decision you will have to make. If you wound up replacing the lines, then conversion wins.

Cost wise on the compressor, the TM21 or a GM part like the A6 or V7 is probably the middle of the road. Retrofit brackets in your case will be a handmade item, but the cross bolt compressor like the TM21 would be an easy job with some heavy angle. The A6 would need more support than just the two bottom holes, so you would need to fabricate a rear mount or top brackets.

The TM31 appears to be the same width as a York, which drops in a mount like that on some trucks - probably the mount you have. That compressor is big enough to run two evaporators, and cool an entire 38 foot coach well. It would probably be overkill unless you plan to add an evaporator and do major work on your coach. Even that big boy will run to 6000 rpm...

BTW, my wife has an '07 Vue and it does cool very well. In my book the A/C is right when the wife brings a sweater to get in my pickup - in july.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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