Any AC compressor conversions for R134A?

[Thunderace1997]

I have a 91 Suburban with the 350 in it. The compressor for the AC has stopped working. The AC was converted to R134A a year or two ago by the previous owner. The truck only has 52k original miles on it. I was told by a shop that the R134A will lower the life on compressors that were designed for R12. Is that true?

If that is true will the remans be set up for R134A or R12? If the remans are set up for R12 is there one set up for R134A that I can swap from another vehicle?

Thanks.

[hatzie]

Compressors can blow out on R134 conversions when the system isn't flushed, vacuumed down, completely charged with refrigerant and filled with Ester oil.

This is how I refit an empty R12 system no matter what refrigerant I use.

Make sure the hoses get swapped to barrier hose. You don't have to change out the hard lines. Remove the crimp collars and crimp on new barrier hose with new collars. An AC shop can do this or splurge $$$ on a Mastercool AC Crimp tool.

Cut off the AC muffler (if there is one) and braze on a muffler bypass tube.

Make sure the o-rings and gaskets get swapped to R134 compatible.

Install R134 fittings and a retrofit label.

Flush the lines, Condenser (If I'm not installing a new high efficiency parallel flow unit), and Evaporator to get rid of any oil and contamination in the system and blow out with compressed air.

Replace the Fixed Orifice Valve with a Variable Orifice Valve (VOV).

Get fresh sealed oil matched to your refrigerant choice. PAG and Ester oils used with R134 (Ester on conversions). Mineral oils are used with R12 and hydrocarbon refrigerants like R290 (propane), R600 (isobutane), and hydrocarbon blends like Envirosafe.

Completely drain the unknown pedigree oil from the new compressor and fill it with a charge of sealed oil in the amount the service manual calls for. That way you know exactly what you've got in the system. No guessing. PAG, Ester, and Mineral AC oils absorb moisture fairly fast. I'd fill with oil just before you install the drier and close the system to minimize water absorption. You can buy oil with UV Dye premixed to avoid overfilling.

Unpack and install a new sealed accumulator/drier dead last. Doing this as the last step in closing the system minimizes the moisture the desiccant pak absorbs.

I hook up my gauges and vac the system all the way down immediately to check for leaks and cut down on the amount of moisture the desiccant pack in the accumulator/drier and the compressor oil absorb from any air left in the system. Alternatively you could sweep the system with several Nitrogen, CO2, or Argon/CO2 charges. Some folks use propane to sweep but it's technically a refrigerant so the EPA could fine you some ungodly sum of money for sweeping with it.

I pressure test, after the first successful vac, with just enough Argon/CO2 from my MIG welding tank to close the Low Pressure Cutoff switch and shoot some UV dye into the system. Run the compressor for a few minutes and check for leaks with a blacklight.

When I'm sure I've got a leak free system I Vac down again for at least 6-8 hours, close the vac/charge valve or disconnect the gauges completely, and leave overnight or longer. If it's still at full vac, after 12+ hours or so, I fill with a refrigerant charge till it gives me good cooling without frost and high head pressure.

A swap done like this usually lasts for years.

[Thunderace1997]

I rarely use the AC but my wife likes the air instead of all five windows open.

So I need to figure out if the previous owner did it correctly.

When I bought it I charged it. It worked great for a week or two and than stopped getting cold. I bought a couple of cans to see if I needed to charge it again and noticed the compressor belt was turning but it wasn't engaging so it couldn't be charged. I'm wondering if the clutch burned out.

If the conversion was done correctly by the previous owner and I have a bad compressor now what would I need to do to the new remanufactured compressor?

[Keith Seymore]

Originally Posted by hatzie

Completely drain the unknown pedigree oil from the new compressor and fill it with a charge of sealed oil in the amount the service manual calls for.

Sub-scribing....

I followed everything you said, except for this new compressor of which you speak: is that a direct replacement for the compressor (same style and model) as what's currently on the truck, or do you recommend a new style/type (like a more modern Sanden or something)?

Thanks in advance -

K

[hatzie]

Originally Posted by Keith Seymore

Sub-scribing....

I followed everything you said, except for this new compressor of which you speak: is that a direct replacement for the compressor (same style and model) as what's currently on the truck, or do you recommend a new style/type (like a more modern Sanden or something)?

Thanks in advance -

K

If the compressor is OK and just low on freon you should still drain and re-fill with Ester oil.
Using a new original style compressor is less time consuming and it'll work OK.
The newer HT6 is supposed to be more efficient so should cool better. But you'll need to get mounting brackets.
Fill any of the above with the right amount of Ester oil because that will put up with any R12 oil that doesn't get flushed out.

If you can find it... there used to be a writeup by Jungle Eddy on the Aircon boards called "How to charge an AC". It outlines how to charge an R12 system, with a refrigerant it wasn't originally designed for, using gauges and thermometers. I saved it somewhere... If I can find it I'll post it here.

[hatzie]

Unfortunately I don't have the posts Eddy has referenced on Vacuum, Flushing, Oil Supply, Leaks etc

--------------
Posted by JungleEddy on September 05, 2001 at 08:17:44: via: or 66.25.151.188

More important stuff.

How to charge an A/C system.

Note: This method will work for any automobile A/C system regardless of refrigerant type. The pressures I list here will only be correct for HC’s.

I have been trying for the past couple of weeks to come up with a “system” that would allow just about anyone to properly charge their A/C system. While this method I have developed is not fool-proof, it yields the closest thing to a perfect charge I have found. I have tested it on three “non A/C” mechanics in the past few days with great success.
First: If you have not read my previous post on vacuum, flushing, oil supply, leaks and fans etc etc, please do so now. You still need a properly assembled system to get proper cooling!

This ENTIRE process makes a few IMPORTANT assumptions!!
1. The ambient air is OVER about 84 degs.
2. You have a set of A/C gauges
3. You do not take shortcuts.
4. You are able to read and comprehend enginsh.

This process will work down to about 80 degs ambient air, but will be MUCH MUCH easier to over charge below 85 degs ambient air!! Relative high side pressures will be lower at 80 degs ambient and pressure drop after wetting the condenser will be less dramatic.

Pull a hard vacuum for a minimum of 15 minutes, 60 minutes is perfect. Static charge the system to about 65 psi while the engine is NOT running.

If you have a low pressure cut out switch on your system you will need to adjust it down to 18-19 psi sometime during this process. Personally, I find it easiest to do this about midway (now) through the charging process. Remove the connector from the switch and turn the adjustor screw about 1 full turn counterclockwise from its factory position. (counterclockwise is less psi, clockwise is more psi, 99% of the time) Start the engine and turn on the A/C, recirc, max fan, and engine at idle. Max fan is important, since it will help keep the evaporator from freezing as you charge. Charge the system slowly (if you have to!) until the compressor stays on fairly continuously at IDLE. The adjustment I illustrated above should give you a cut out psi of 12-18 psi. Watch your low side gauge and SLOWLY increase engine rpm. The low side pressure will drop slowly but substantially because you are still undercharged. Watch it drop from 20+ psi down through the teens and carefully note where the compressor cuts out. Return the engine to idle and pull the connector to the cut out switch and adjust it accordingly. Try this several times until, as the engine is slowly revved the compressor cuts out at about 18-19 psi on the low side.

The Charge:
Bring the engine rpms up to a continuous 1200-1800 rpm. Begin to add refrigerant (if you have to) SLOWLY until you notice that the air at the vents is noticeably cooler than the ambient air, say at about 65-75 degs or so.
At this point grab your garden hose and hose down the condenser; soak it once only. Your pressures will drop dramatically. The high side should drop below 150 and the low side should drop low enough to cycle the compressor, or if the switch is temporarily “jumped” the low side should be well below 20 psi. I prefer at this stage to jump the connector to the pressure switch to keep the compressor running continuously. It makes the process go much faster, but you risk freezing the evaporator. Now, watch the system pressures rise as the water evaporates and the heat in the system and stabilizes and equalizes. This can take a long time if you have a mechanical radiator fan. The point where the pressures remain relatively constant is called equalization.

Here is the key:
(After wetting the condenser) As you are watching the high side pressure rise from 160psi through (potentially) about 205psi the LOW side should REMAIN from 21-24 psi. If the high side never sees 145+psi you are still low on charge as long as the ambient is 85 degs or above. If as the high side needle swings through 160psi the low side is still below 20psi, you will add more refrigerant AFTER wetting the condenser again and dropping the pressures. Keep doing this until the low side remains at 21-24 psi while the high side swings through 160psi and finally settles at equalization (no more rise) Keep the engine rpms constant and wait for equalization (or close) each time before wetting and charging. If you are going carefully and slowly you could see a high side over 225 at equalization BEFORE you reach a full charge. The high side will DROP as you come closer to a full charge. Be aware that if you over-charge, the high side will climb again and never come down.

Note: If the ambient air is above 95 degs, stop watching the low side after the high side climbs past 205 or so. Especially if you have weak fans.

Note: Take your time and wait for equalization and water evaporation off the condenser before adding refrigerant. An overcharge can occur with no more than an extra 1.5 ounces of refrigerant!!

You can double-check your work at any time (and I suggest doing so) by waiting for full equalization and stabilization of pressures. Then, carefully MIST water into the condenser SLOWLY SLOWLY dropping the system pressures and watching for the same readings on the gauges as listed above.

When finished you should have a sweaty return line all the way back to the compressor. When the return line begins to feel chilled over the first portion of its length, you are approaching full charge. Do not forget to reconnect the low pressure cut out switch!

Do not consider your vent temps accurate until the vehicle has been driven for about 10 minutes at moderate highway speeds!!!! Idle low side pressure should not exceed 40 psi (34-38 actual) if everything is working well; good fans etc….

The idea here is that the compressor should NOT cycle when ambient air temps are above 81-84 degs.

Interesting note for tech heads: If you are charging SLOWLY. You will find at first that the high side will be at a higher pressure, after equalization, on a low charge than at a correct charge! Remember, raised heat = expansion and/or pressure.
Why: (basically)
Within a certain range, the pressure in the condenser (high side) is MUCH more affected/determined by the temperature of the refrigerant than its volume.
ALL THINGS BEING EQUAL, the condenser has the ability to lower the temperature of the refrigerant passing through it “X” amount and no more. The compressor, in compressing the refrigerant, heats or raises the temperature of the refrigerant “Y” amount. Lets say the temperature of the refrigerant entering the compressor via the return line is “Z”. So the final temperature “T” of the refrigerant that gets to the orifice/exp valve is: Z+Y-X=T
If we could lower the value of “T” the entire system would work more thermally efficiently and at lower pressures on the high side. So, ALL THINGS BEING EQUAL, you could 1. get a larger condenser and raise your “X” value or 2. lower the value “Z”.
A full charge on an A/C system will not only have enough refrigerant in it to keep the evaporator “chilled”, but JUST ENOUGH that the line leaving the evaporator and returning to the compressor will also have substantially cooled refrigerant in it THUS LOWERING YOUR “Z” value!! Hello!!
Note: Over charging will allow actual condensed refrigerant (liquid) to make it all the way back to the compressor. As we all know, you cannot compress a liquid…boom/screech.
----------------

[Keith Seymore]

Thanks for the reply and for reposting those instructions.

Is there a way to check one's existing compressor to see if it is ok? (ie, spin it by hand, or put some current to it)?

Also - I have a stash of R12 so I intend to recharge with that once I get this all sorted out.

K

[Keith Seymore]

Originally Posted by hatzie

This ENTIRE process makes a few IMPORTANT assumptions!!
1. The ambient air is OVER about 84 degs.
2. You have a set of A/C gauges
3. You do not take shortcuts.
4. You are able to read and comprehend enginsh.

I'm good on most of these, but not sure I am able to reach and comprehend "enginsh"...



K

[hatzie]

It's his procedure he can call it anything he likes.

[hatzie]

Originally Posted by Keith Seymore

Thanks for the reply and for reposting those instructions.

Is there a way to check one's existing compressor to see if it is ok? (ie, spin it by hand, or put some current to it)?

Also - I have a stash of R12 so I intend to recharge with that once I get this all sorted out.

K

I used quality rebuilt compressors on my project rigs... but that tends to be expensive especially if you're on a tight budget.

Here's a post on checking out a compressor from the AC Forums FAQ.
http://www.autoacforum.com/messagevi...threadid=12050

I flush the evaporator, condenser, and hardlines if the system has been open for any length of time to get rid of the old moisture and critter ridden oil. I dry them thoroughly with compressed air and leave em out in the sun. This guarantees you have the right oil charge and no more.

If you're going to run dye in the system permanently, like I do, you can get oil with UV dye premixed so you don't overfill.

[hatzie]

Originally Posted by Thunderace1997

I rarely use the AC but my wife likes the air instead of all five windows open.

So I need to figure out if the previous owner did it correctly.

When I bought it I charged it. It worked great for a week or two and than stopped getting cold. I bought a couple of cans to see if I needed to charge it again and noticed the compressor belt was turning but it wasn't engaging so it couldn't be charged. I'm wondering if the clutch burned out.

If the conversion was done correctly by the previous owner and I have a bad compressor now what would I need to do to the new remanufactured compressor?

You can change the clutch and pulley without opening the system if that's the only issue.

[Keith Seymore]

Originally Posted by hatzie

I used quality rebuilt compressors on my project rigs... but that tends to be expensive especially if you're on a tight budget.

Here's a post on checking out a compressor from the AC Forums FAQ.
http://www.autoacforum.com/messagevi...threadid=12050

I flush the evaporator, condenser, and hardlines if the system has been open for any length of time to get rid of the old moisture and critter ridden oil. I dry them thoroughly with compressed air and leave em out in the sun. This guarantees you have the right oil charge and no more.

If you're going to run dye in the system permanently, like I do, you can get oil with UV dye premixed so you don't overfill.

Thank you; still gathering parts and learning as much as I can.

I was able to fix my Suburban (R134a) but it was a slam/dunk compared to what I'm getting in to know.

K

[8lugnutz]

Originally Posted by Thunderace1997

I needed to charge it again and noticed the compressor belt was turning but it wasn't engaging so it couldn't be charged. I'm wondering if the clutch burned out.

I am dealing with this same issue. Mine appeared to be converted to R134A already, but my clutch is definitely out too. It can be replaced without pulling the compressor. I will be replacing it tonight and updating the results on my build page.

[hatzie]

There is a low pressure cutout switch in the clutch circuit.
If you're low on refrigerant it'll keep the compressor clutch from engaging.