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Discussion Starter · #1 ·
So the A/C in this 90 W150 has never been great since my dad converted it to R134a. I am not to sure what all he did to convert the system, but he did have it working, I think. I found a leak to be in the Schrader valves. Well I was able to replace the one no problem, but the other one broke off in the line. For the life of me I was not able to get it out so I needed to get a new line.

I installed the new line last night, as well as a new filter drier, added some oil and closed the system up. I vacuumed out the system to 30 inHg and it stayed above 20 for 15 minutes. I then proceeded to fill it with R134a. This is where I am having some issues.

I looked on here and saw where the pressures should be for the high and low side, I also saw what the pressures should be as indicated on this site:

http://dodgeram.info/tsb/1995/24-01-95.htm

Here is my issue. When I stop filling the system the low side is reading a vacuum and the high side is only reading about 60-70 psi. Which from what I can find here is really low. I have not found anyone that had a similar issue so I am kind of stumped on what avenue to go. I see people have center vent temps into the 40-50 F, but I am lucky if I get this thing down to 60 on a 60 deg day, let alone a high temp high humid one.

When I pulled out my Snap on refrigerant leak detector I was not able to see any leaks at the connects I made on the system.

Where do I go from here?
 

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If low side is in a vacuum, sound like the txv is bad or either that Schrader has sucked into the txv or compressor. Either way freon is not passing through that txv and or evap coil. My guess is txv.
 

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Discussion Starter · #3 ·
forgive my limited knowledge, but what is the TXV?

I did check for leaks again last night and it did appear that the compressor may have a small leak around the shaft.
 

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Discussion Starter · #5 ·
Gotcha,  Thermal expansion valve.

So in order to do this conversion properly should I get the following parts?
Four season 33555 filter/drier
FOUR SEASONS 38848 expansion valve
four SEASONS 58101 compressor

Would I need to get the high pressure cut out switch and high pressure relief valve as well? If so where do I get them?
 

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I wouldn't bother replacing the compressor unless you just want to and/or it's cheap enough. I mean, the compressor is working, correct?

I would honestly look at replacing the condenser over the compressor in your situation with a retrofit. The condenser is going to be your biggest issue by far with R134.

You ideally want to find a parallel flow condenser to retrofit in. Without that, your R134 conversion is frankly never going to work very well unless you're in a northern or coastal state - despite the random person here and there claiming 40 degree center vent temps. Claimed center vent temps should always be taken with a grain of salt - it's all relative to geographic location, ambient temp and humidity, time of day, was the truck at idle or driving down the highway, etc. Frankly the only center vent temp number that should matter is what it puts out AT IDLE on a 100 degree day. I know that's for darn sure what I care about here in Texas.
 

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Discussion Starter · #7 ·
Is there a known part number for a cross flow condenser?

and I am one of those people up in the northern States.  But yes the compressor is working.  It turns on and cycles.  However, I am reading a small leak behind the pulley.
 

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No known direct-bolt-in parallel flow condenser part number that I know of offhand. There are any number of universal ones that would fit just fine and they're cheap too but would require a little bit of AC hose beadlock/crimp work on your part to hook it up with your system. If you're not familiar or comfortable with hose work/beadlock stuff then probably not worth your trouble to do the parallel flow condenser.

If you're in PA I'm sure you can more than likely get away with a factory serpentine style. HOWEVER, I would suggest still replacing the condenser. No matter how hard you try, you can't properly flush a condenser. Your factory serpentine condenser is now going to be filled with both mineral oil from the old R12 setup and also now PAG or whatever your dad used for the conversion. This reduces heat shedding ability as well as makes your total system oil volume a guessing game.

You can get a new condenser for ~$75 and it's cheap insurance to help you start much closer to an empty system in terms of oil. Assuming you replace the compressor (I prefer to drain whatever oil comes in them), blow out your lines, replace the drier, you'll just have a little bit of oil left in the evaporator (maybe an ounce or so).

This is a very overlooked aspect of AC work from do-it-yourselfers. If you don't know exactly how much oil you have in the system (or too much) you're always fighting with one hand tied behind your back.
 

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Discussion Starter · #9 ·
James, thank you for that information.

Would the parts I listed for four seasons be good to replace to make sure the system can handle the R134a? By switching to R134a do I need to worry about the pressure relief valves and high pressure switch as outlined in the TSB I attached above?
 

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carfreak6970 said:
James, thank you for that information.

Would the parts I listed for four seasons be good to replace to make sure the system can handle the R134a? By switching to R134a do I need to worry about the pressure relief valves and high pressure switch as outlined in the TSB I attached above?
Typically, people don't change the switches/valves when retrofitting. There's likely no reason to unless the OEM switch ranges are just out of whack for R134 pressures. R134 does run higher operating pressures than R12 but even at that there's usually no reason to bother with your switches.

Most specifically, these trucks run rather simple systems though. A typical modern automotive AC system has both a low/high pressure cut-off switch AND a temp probe in/on the evaporator that actually cycles the compressor but this system does not. These have a low pressure switch (in-line near the blower box) and ALL they have other than that is a high pressure relief valve built into the compressor itself. The factory low side switch has 22 PSI and 49 PSI ranges and is basically the only thing that cycles the system on these trucks. As your compressor cycles, low side pressure should drop, hit the 22 PSI cut-off, and kick the compressor off. Then when the low side pressure rises back up to 49 PSI it'll kick back on.

The high pressure relief valve - and you will have one on a new aftermarket replacement compressor - is actually just an emergency/last resort pressure switch and not meant to be used to cycle the system. If your system is operating properly it should never come into the equation. It merely prevents compressor damage in the event pressure skyrockets.

The factory service manual mentions the pressure relief valve built into the drier but my OEM system had no such thing there, just on the compressor. Doesn't really matter where it's located though, but your system will have a high pressure relief valve and I'd bet it's on the compressor not on the drier.

I believe there were two different compressors available in these trucks. I'm not sure offhand the model number specifics so I can't confirm if that part number will work for you. I will say I have not had good luck with Four Seasons "moving" parts (compressors, power steering pumps, that sort of stuff) over the years for a variety of applications and prefer not to use Four Seasons unless I have to. I have had good luck with the Chinese clone compressors from both UAC and GPD. Rock Auto also probably has an all-in-one kit that includes compressor, gaskets, drier, and expansion valve that you should be able to pick up cheaper than just the Four Seasons compressor - I'd bet a smidge over $200 plus be sure to Google and add the 2% discount code on top of that. Something else you might do is get the individual part numbers and check eBay to see if you can find the random listing for even cheaper than Rock Auto.

*edit* - I just now noticed you posted a TSB. That's very interesting and I have never seen that before. I notice they actually list a part number for pressure switch and a quick Google search looks like you can still get the switch (PN 4773190 and widely available aftermarket). However, the place they want you to use this switch is the "high pressure relief valve" built into the drier, but, again, my factory system didn't even have such a valve. Does yours?

ToxicDoc said:
Not to disparage a forum favorite vendor, but those are just severely marked up universal condensers. If the OP wants to add a parallel flow condenser, just buy the exact same thing direct from Amazon or eBay for 1/3 the price.

A quick Google search -

https://www.amazon.com/CNFP1826-Universal-Condenser-Parallel-ring/dp/B01CKNHNAE
 

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Sorry to hijack this thread. Does anyone have the torque specs for the parts?
I just bought a new compressor and some parts to get mine working, but I've not seen anyone speak of proper torque for the drier, txv, etc attachments. I think this would be important.
 

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I can't speak for "improvement" because my truck started without AC, but I installed their condenser and switches and my system works very good.
 

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johnnycashjunkie said:
Sorry to hijack this thread. Does anyone have the torque specs for the parts?
I just bought a new compressor and some parts to get mine working, but I've not seen anyone speak of proper torque for the drier, txv, etc attachments. I think this would be important.
Definitely not two ugga duggas. This is one of those things that is near impossible to describe in text and this isn't really helpful at all, but the answer is "tight enough". It just kind of takes a feel for it. You can sort of feel how tight the OEM stuff is when you loosen it. Sorry for the most unhelpful answer ever lol.
 

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ToxicDoc said:
I can't speak for "improvement" because my truck started without AC, but I installed their condenser and switches and my system works very good.
What is your high and low pressure readings on the upgraded system, and does your compressor cycle on and off?
 

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JohnB said:
What is your high and low pressure readings on the upgraded system, and does your compressor cycle on and off?
Haven't seen my truck in a while, friend is borrowing it, but I recall using a high side of about 2.2 x ambient Fahrenheit to set it up, with a low of 35. Since I wasn't using a factory setup, I had to go by pressure and not weight. I have a small supplemental fan on the condenser to reduce head pressure.

And yes, I have a Sanden compressor that cycles on/off. I used a lot of parts from Bouchillon.
 

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I went down the AC fix road here in Oklahoma 3 years ago in my black daily driver D150. I refitted a new parallel condenser with small pusher fan at the condenser inlet that comes on when the compressor engages. The rest of the work basically came from a small AC shop here in town working with my advise. My compressor too leaked at the shaft, it’s common. For the money I replaced it with a Sanden unit $250.  New drier $25. My original TXV (expansion valve) was replaced with an original R12 replacement.  After running the setup for a year a gasket let go and I headed back to the AC shop. I decided to give another TXV rated for 134A a try along with the gasket fix. My system works good. Has a pesky slow leak but works good. I just added 1/2 can to her three days ago. 89° ambient temp 60% relative humidity. Added freon till I averaged 30 psi low side 270 psi hi side.  At 1500 RPM. I’ve got a digital thermometer in vent of the truck and monitor vent temps driving down the road. Yesterday took it for 30 min drive. I watched my vent temps rise and fall between 40°-44° as I went down the road. My system was cycling on and off as it should.  You may be interested in the three key things I think makes the system work. Not great,  but good for the money invested and without a bunch hacking.
1. Parallel condenser UAC brand. Fits a Dodge 1994 B2500. Forgot the part number and exact price, it was around $150. The vans changed to 134a  in 94 for sure then and they kept the same block style line fitting that your lines will bolt right to. I modified the radiator support a bit and made metal tabs for the brackets. Otherwise the hoses went where they should and fit like they should. Later on I looked at Rock Auto picture of a condenser for my truck. It looked like it was a parallel design ( in the picture). So check that out, you may get lucky and not have to do any fab work. 
2. While I was there making the van condenser  fit I made a bracket and mounted a 10” pusher fan $60, where the hi side pressure line enters the condenser I wired in a relay to work the fan on with the cycling of the compressor.  It may not be necessary for your climate. Be sure your getting enough air flow, maybe get a new fan clutch.
3. Key point here: I used UAC part number 9418C,  TXV (expansion valve) $30. This one as well has the same hose fitting for the R12 system but the valve is rated to work with 134A. It fits a 1995 B2500 as well. A little bending adjustment for the for the low pressure switch terminals was made because their  on the opposite side (no big deal) 

I get a lot of enjoyment seeing newer vehicles  with the windows down and sweat on the drivers brow.
 

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Discussion Starter · #20 ·
Thank you all for the tips and suggestions.  When I took the system apart I noticed a lot of crap in the expansion valve. Which would be the blockage that the help line at 4seasons said is causing a suction on the low pressure side while running the system.

So I got the four seasons compressor, expansion valve, and filter/drier.  I also got a new condenser (Dont believe it is a parallel flow).  I got their A/C flush stuff and cleaned out the lines as well as the evaporator.  I got the system all together and I was able to hold a 30 mmhg vacuum for over 2 hrs.  Which it was not capable before.  I added the R134a and it blows cold.  I am happy with the system.  May not be the coldest system out there but it works well.
 
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