Interest in A/C writeup?

[Minuit]

A recent thread on here got me thinking about this, and at least where I live A/C season (tm) has officially begun. What interest would there be on a DIY writeup on proper car A/C system work? It's surprisingly hard to find resources on the internet for doing this stuff right. I spent a while watching some Youtube tutorials on the subject and so far I haven't found one that I liked.

 

I'm not talking recharge kits here, I'm talking the real deal. I have what I'd consider to be a golden opportunity for a real instructional writeup on MJ A/C coming up - my own lovely '89. I know nothing about the history of that truck's A/C, but there are a few common PO hacks to correct. There'd be plenty of material to cover - R-134a conversion, most likely a few parts replacements, performance testing, etc.

 

Would the club at large get enough benefit out of this to make it worth the effort of putting together?

 

I know there are a few other MVAC guys here, and I'd like to know what they think too.

[Strokermjcomanche]

If you end up doing a writeup , I have a bunch of information from my NOS A/C kit including troubleshooting, part numbers , etc etc . 

[Blaine.D]

2 hours ago, Minuit said:

'm not talking recharge kits here, I'm talking the real deal. I have what I'd consider to be a golden opportunity for a real instructional writeup on MJ A/C coming up - my own lovely '89. I know nothing about the history of that truck's A/C, but there are a few common PO hacks to correct. There'd be plenty of material to cover - R-134a conversion, most likely a few parts replacements, performance testing, etc.

 

Would the club at large get enough benefit out of this to make it worth the effort of putting together?

I say it would be a benefit and would be worth the effort to put together because of the lack of info and writeups. Personally, I know I would benefit because I'm close to doing the conversion on my truck and I would add what parts are needed to be changed and/ or modify to work with r134a.

[Keyav8r]

There are a couple of members with A/C knowledge who helped me when I was working on my ‘91’s A/C.  One is Marine1Texas and the other is Noritake (can’t remember the other part of his handle).  Haven’t seen posts from either lately, but then I don’t read everything that’s posted.

[knever3]

I would love that! After my Renix/96 stroker swap I would love to add A/C. Not looking forward to all the figuring what I need now.

Sent from my SM-G920P using Tapatalk

[Fernando87mj]

I'm in. I’m also curious on learning more about the evaporators used in these trucks. From what I’ve seem here is that the factory a/c used a different evaporator than the dealer installed. My 88 comanche has dealer installed a/c and my 87 has factory. But someone broke the pipe going into the evaporator on my 88 so i need to replace the evaporator but what holds me back is knowing if i can even still find the evaporator for my 88. 

[DIRT_NASTYY_]

I'm interested, I have A/C but its doesnt blow cold and I know nothing about them. 

[davidh190]

I’d read it for sure. My system needs a complete overhaul


1989 Base
4.0 L
Auto
Long bed
2WD

Sent from my iPhone using Tapatalk

[floridaftwman]

I’m definitely interested. I’m having some issues with the vacuum lines that control the vents on my 88 Pioneer. I’ve got it jimmy rigged, but I’m afraid the repair isn’t gonna last....


Sent from my iPhone using Tapatalk

[DesertRat1991]

Interested. I've been compiling parts to do a ground-up install on my '91. Still got lots to learn.

[Nashmanche]

I think it would be very beneficial. Sooner or later many of us are going to need or want the information. 

And neighbor, let me know if you ever need an extra set of hands on a project. I am always willing to learn.

[kryptronic]

Yes, please!

[watchamakalit]

Put me down as a subscriber. It would be a wonderful addition.

My build: https://r.tapatalk.com/shareLink?url=https://comancheclub.com/topic/8033-finally-found-onenow-it-has-a-new-floor/&share_tid=8033&share_fid=53169&share_type=t

[Swampy]

I am definitely interested, mostly because I have I have all the components but no cool air, just heat and that's no Bueno in Florida

[Keyav8r]

Fernando87mj - The two parts I couldn’t find new when I was doing the A/C on my ‘91 were the evaporator and one of the hoses.  Those I picked at a Pull-A-Part from XJs that still had pressure on the system (showed that the evaporator and hose were good).  Can’t remember which hose I couldn’t find.  I believe the factory evaporators were the same ‘88 - ‘91, possibly ‘87 also.  

Actually, I’ve got a couple of used evaporators left that I think are good.  I tested them by putting 125 PSI air pressure in them and submerging them to look for bubbles.  The problem is that there are few ‘87 - ‘91 XJs showing up in the junkyards, at least around here.

There is a thermistor (?) that inserts into the evaporator.  I don’t have that part as they tend to break or pull apart when you try to remove them.  Couldn’t find that new either.  I can send you a photo of the ones I have so you can see if yours is the same.

Getting the right size O-ring for each joint is very important as the joint will leak if the O-ring is not correct.  I think I bought 3 packs of O-rings to get enough of the right ones.  Hopefully, Minuit will cover that in his write-up.

[Fernando87mj]

14 hours ago, Keyav8r said:

Fernando87mj - The two parts I couldn’t find new when I was doing the A/C on my ‘91 were the evaporator and one of the hoses.  Those I picked at a Pull-A-Part from XJs that still had pressure on the system (showed that the evaporator and hose were good).  Can’t remember which hose I couldn’t find.  I believe the factory evaporators were the same ‘88 - ‘91, possibly ‘87 also.  

Actually, I’ve got a couple of used evaporators left that I think are good.  I tested them by putting 125 PSI air pressure in them and submerging them to look for bubbles.  The problem is that there are few ‘87 - ‘91 XJs showing up in the junkyards, at least around here.

There is a thermistor (?) that inserts into the evaporator.  I don’t have that part as they tend to break or pull apart when you try to remove them.  Couldn’t find that new either.  I can send you a photo of the ones I have so you can see if yours is the same.

Getting the right size O-ring for each joint is very important as the joint will leak if the O-ring is not correct.  I think I bought 3 packs of O-rings to get enough of the right ones.  Hopefully, Minuit will cover that in his write-up.

Thanks! Thing is I haven’t pulled my dash or anything. I’m just curious about the evaporators. I have a suspicion that my 88 comanche has a different evaporator since it has dealer installed ac than my 87 that has factory a/c. The lines coming out of the evaporator onis completely different than the one on my 87. Here’s a pic of the lines 

[Keyav8r]

That’s definitely different than either the ‘88 or the ‘91 I had, both of which had factory air.

[Minuit]

Looks like an A/C writeup is going to happen after all, there definitely seems to be demand for it. Can't guarantee a time table, but I'll start on it in earnest after I finish documenting my ZJ rear disc swap. I'll be starting a new job relatively soonish so my playing around with Jeeps time might get cut off abruptly. I might throw a proposed table of contents in here if I get time.

 

On 5/13/2019 at 11:23 AM, Nashmanche said:

And neighbor, let me know if you ever need an extra set of hands on a project. I am always willing to learn.

 

On 5/12/2019 at 7:21 PM, Strokermjcomanche said:

If you end up doing a writeup , I have a bunch of information from my NOS A/C kit including troubleshooting, part numbers , etc etc . 

That would be extremely helpful.

 

The biggest thing I think I'm going to need help with is factory vs. add-on A/C and the various parts differences. My '91 definitely has factory A/C and I think my 89 does as well (see? I don't even know if my own truck has it!). Also, I have no info about the various A/C systems as fitted to the 2.5L.

 

As to the thermistor in the evaporator, I'm fairly sure they're different between Renix and HO. I remember seeing a replacement for the HO years from a different model that was still available. It's quite expensive but I consider it worth it.

 

NOS 91+ evaporators were available on Team Cherokee last I checked. What they won't tell you is that they're RHD evaporators and are not an exact match, but they do fit. I have one in my 91 and IMO it's almost worth it to keep the evaporator probe alone. After running my system WITH the thermistor, I recommend that it be kept if at all possible. In certain situations, my '91 cycles on the evaporator probe rather than the low pressure cut-off switch.

[youngfred]

...

 

 

I am very interested.

 

I was about to start gathering parts

to get some cold air going, again.

 

 

 

 

 

 

youngfred

 

 

 

 

 

 

 

 

 

 

 

 

[Keyav8r]

I was able to re-use the thermistor probe when I did the ‘91s A/C.  I have one on the shelf with the used evaps.

I couldn’t find new evaps or thermistors when I was looking around 2 years back.  However, I don’t remember if I checked Team Cherokee.  If I had been able to find them I would have paid the price because I did NOT want to have to pull the dash again. 

[buxmj]

Thanks Jeremy for doing this, great idea!  

 

Buck

[schardein]

I think doing this will really benefit the community.

 

A few years ago, I did a bunch of research, bought a set of gauges, a vacuum pump, flush gun & fluid, and a 30lb can of R-134.  Then I fixed my XJ, MJ, and Silverado.  Replaced everything but the evaporator, which I flushed, on all 3.  All were a success, but the Silverado cools much better than the XJ or MJ.  And the MJ needed a recharge this year, which wasn't a problem with a mostly full 30lb can.

 

Jeremy, I think we've talked about this before, but I used parts meant for a 96 XJ.  I like the way the hoses are ran more than the original 91.  Not sure I can recall the details, but the new dryer also required some mods to make work.  And orientation of the oil filter can be problematic.

 

Not sure if I have pics, but happy to help any way I can.

[Minuit]

28 minutes ago, schardein said:

Jeremy, I think we've talked about this before, but I used parts meant for a 96 XJ. 

I... may have taken some slight inspiration from the system you built. By that, I mean I did the exact same thing.

 

When I get down to business on this, I'd be happy to accept any help from anyone willing to lend it that knows their stuff. It'll make for a better end product if multiple qualified people review it.

[Minuit]

Pete asked about it, so here's a little something. This will be part of an appendix of the final AC writeup. I put this together because I had the time to, and because I personally wanted some answers. This is the writing style I plan to use for the entire thing. If there's any questions, comments, concerns, cries of outrage, or calls to action you have after reading this, let me hear them. My free time is about to take a nose dive, because I'm starting a new job and it's been hectic. I hope to have a table of contents fairly soon. I may release the writeup in chunks, or I might put the whole thing out one day all of a sudden. Not sure.

 

The Heater Control Valve

For as long as there have been Jeep forums, one of the most common pieces of wisdom you'll see thrown around is "get rid of the heater control valve and throw it in the trash". It's a 30 year old piece of plastic with coolant flowing through it, so it presents a definite possibility for leaks. I threw mine away several years ago on this advice. However, Jeep wouldn't have installed it for the first 12 years of the XJ's run if they didn't have a reason for it. That reason is very much connected with the subject of this writeup, so let's take a look at it.

 

Why worry about any of this? Let's look at a diagram of the MJ's HVAC system.

(source: 1990 Jeep factory service manual)

 

 The A/C evaporator is the first thing the air passes through after leaving the blower motor. This is to provide dried air (via the A/C evaporator) no matter the blend door position - very useful when defrosting the windows, and if the driver would prefer to have dry heat in the cab. Unfortunately, that means that everything that happens to the air after it leaves the evaporator is out of the A/C's hands. Even if you want the coldest possible air, the cold air still has to pass through the rest of the HVAC box and out to the vents, in relatively close proximity to the heater core. If coolant is flowing through the heater core, the heater core will be very hot, and it will warm up everything around it. As it flows through the hot ducting, the air will warm up a little.

 

The heater control valve was Jeep's solution to this problem. When the driver commands the coldest air possible, the valve closes and prevents hot coolant from flowing into the heater core, which prevents the heater core from warming up the surrounding duct work. Since even cold air has to pass right next to the heater core, this can and does make a difference to A/C performance. Even if you don't have A/C, not having any hot coolant flowing through the interior will help keep cabin temperatures down.

 

The valve is closed in the "OFF" and "VENT" positions. In all other positions, the valve is closed any time the temperature selector is in the "full cold" position.

 

So, let's put some numbers to this. To simulate a working heater control valve, I bypassed my heater core and went for a ride.

 

To summarize my results, all else being equal the air at the vents with the core bypassed is between 3 and 7 degrees cooler when the truck is at operating temperature. These measurements were taken on two back to back days at a temperature of around 83 degrees. In the world of A/C performance, seven degrees is a big difference. It can separate a "decent" system from a "good" system. In my case, this allowed for air in the high 30s at speed on an 83 degree day. I live in the humid South, and I want all of the A/C performance I can possibly have, so a seven degree improvement is worth the effort.

 

After this test, I've changed my stance on keeping the valve. If you are interested in maximizing your A/C performance, I suggest that you keep the heater control valve, and replace it if it is leaking. The valve is still available in the aftermarket and you may be able to find Mopar valves in inventory. The 1991 and later part number for 2.5L and 4.0L engines is 56005900. The 87-90 part number is 52003226 for 4.0L engines, 56002522 for 2.5L engines, and J3222290 for the 2.1L diesel engine. For an open cooling system, use the later part.

[DesertRat1991]

7 hours ago, Minuit said:

Pete asked about it, so here's a little something. This will be part of an appendix of the final AC writeup. I put this together because I had the time to, and because I personally wanted some answers. This is the writing style I plan to use for the entire thing. If there's any questions, comments, concerns, cries of outrage, or calls to action you have after reading this, let me hear them. My free time is about to take a nose dive, because I'm starting a new job and it's been hectic. I hope to have a table of contents fairly soon. I may release the writeup in chunks, or I might put the whole thing out one day all of a sudden. Not sure.

 

-snip-

 

Great info!  I'm really looking forward to your chapters covering "parts selection for dummies."

 

I'm trying to piece together an R134A setup for my 91 and have already sourced the HVAC box and dashboard control panel from a '95 XJ.  I'd like to replace the heater core and evaporator.  Do you have any thoughts on copper vs aluminum for these parts?  My understanding is that copper transfers heat better, but the copper units aren't made entirely of copper.  On the other hand, the aluminum units are all aluminum so they end up working better.  

 

Also, does this UAC 4366A parts kit look like a good kit to continue building around?  I like that it includes a parallel flow condenser: 

https://www.rockauto.com/en/moreinfo.php?pk=9826464&jsn=365

 

If I can nail these items down I think that just leaves 4 hoses and a pressure switch left to find.  The '91 looks to be pre-wired for the compressor and pressure switch.  Am I missing anything?

 

Thanks.