1990 Buick Riviera changing from R12 to R134A

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harryjames001
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1990 Buick Riviera changing from R12 to R134A

Post by harryjames001 »

Hello Everyone
I am new to this site and looking for some advice. I recently purchased the above car and I would like to get the A/C to work. I dismantled the system with the intentions of fitting a new compressor, (old H6 was covered in compressor oil), accumulator and orifice. The system had been evacuated and then I tried to drain the oil from the compressor, it was empty. I looked at the orifice to see if there were any metal filings and very few were found. The compressor turned over but was not entirely free, which is what I would expect to find, if the bearings were in good condition. It would bind up in one position. The questions which I would like to ask include;
1. Do I need to flush out the evaporator with a solvent?
2. Do I need to replace or could I get away with flushing the condenser, (cost of new condenser vs cost of several quarts of solvent)?
3. The new compressor comes with instructions to use PAG 46 oil and not PAG150 as GM frequently used. There was no mention of using Ester Oil? What else would you recommend I do?
Your comments would be greatly appreciated.
Thank you
Harry
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JohnHere
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Re: 1990 Buick Riviera changing from R12 to R134A

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harryjames001 wrote: Tue Jul 06, 2021 7:21 pm The questions which I would like to ask include;
1. Do I need to flush out the evaporator with a solvent?
2. Do I need to replace or could I get away with flushing the condenser, (cost of new condenser vs cost of several quarts of solvent)?
3. The new compressor comes with instructions to use PAG 46 oil and not PAG150 as GM frequently used. There was no mention of using Ester Oil? What else would you recommend I do?
Your comments would be greatly appreciated.
Thank you
Harry
1. Yes. All the old mineral oil must be removed.
2. You can flush the older tube-and-fin condenser rather than replacing it, providing it's in good condition. I don't know about a cost comparison.
3. The compressor manufacturer calls for PAG-46, so I would use that. No need for POE (ester) oil unless you suspect that traces of mineral oil will remain in the system.
harryjames001
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Re: 1990 Buick Riviera changing from R12 to R134A

Post by harryjames001 »

Hello John
Thank you for taking the time to reply to me. After I posted my message yesterday, I went online and found a new condenser for $67 plus shipping and taxes, (at Rock Auto). I figured that even though the original condenser was in good condition, it would still take about 3 quarts of solvent to clean it out properly and that would cost more than $60. Now what I have to contend with is flushing out the evaporator and the lines to ensure that they are "oil" and "R12 gas" free. This I am confident of doing with the flushing equipment which I have. From what I have read I am supposed to fill the compressor up with 3 to 4 ounces of PAG46 and put the same amount in the accumulator and this will ensure that the new oil is circulated through the system? I would appreciate you commenting in this? Thank you once again. Regards Harry
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JohnHere
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Re: 1990 Buick Riviera changing from R12 to R134A

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harryjames001 wrote: Wed Jul 07, 2021 7:08 pm Now what I have to contend with is flushing out the evaporator and the lines to ensure that they are "oil" and "R12 gas" free. This I am confident of doing with the flushing equipment which I have.
I wouldn't worry about the R-12, which will be long gone. You definitely want to remove all traces of the mineral oil, though, as well as all the flushing solvent afterward. Both are crucial. A good, deep evacuation will remove any moisture and air from the system later. I recommend using Double End Capped PAG-46 (DEC PAG) if you can get it.
harryjames001 wrote: Wed Jul 07, 2021 7:08 pm From what I have read I am supposed to fill the compressor up with 3 to 4 ounces of PAG46 and put the same amount in the accumulator and this will ensure that the new oil is circulated through the system?
Your vehicle originally called for 38 ounces of R-12 and 8 ounces of mineral oil. Therefore, I would distribute the PAG-46 as follows: 4 ounces in the compressor, 1-1/2 ounces each in the evaporator and condenser, and 1 ounce in the accumulator. Up to four ounces in just the accumulator alone would be too much, IMHO, and might risk damage to the system.

As for the refrigerant, an original R-12 system generally needs less R-134a when converted. Your vehicle will probably cool best with a charge weight of between 27 and 30 ounces. I would start at the lower amount while monitoring the pressures and center vent temperature. Add refrigerant a little at a time as necessary to lower the vent temp while keeping the pressures in the normal range.

The tutorial titled "Minimum requirements for converting a system to R-134a" in this same forum, "Automotive Air Conditioning Procedures, Tips and FAQ," provides additional information.

Be sure to use an accurate refrigeration scale to weigh-in and keep track of the charge weight so that you know where you are at any given point.
harryjames001
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Re: 1990 Buick Riviera changing from R12 to R134A

Post by harryjames001 »

Hello John
I have finally got all the necessary parts and materials to change the system to R134A and as you suggested I have brought a set of scales and a temperature "gun". I found the Double Ended Capped PAG46 on EBay. I will get into doing the job today and fit the new condenser, flush out the evaporator and lines and fit the new compressor.
I would like to thank you for taking the time to give me your expert advice and it is very much appreciated. I will let you know how it all goes in the coming days and once it is completed.
Thank you once again. :D
Regards
Harry
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JohnHere
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Re: 1990 Buick Riviera changing from R12 to R134A

Post by JohnHere »

harryjames001 wrote: Thu Jul 15, 2021 12:08 pm I have finally got all the necessary parts and materials to change the system to R134A and as you suggested I have brought a set of scales and a temperature "gun". I found the Double Ended Capped PAG46 on EBay. I will get into doing the job today and fit the new condenser, flush out the evaporator and lines and fit the new compressor.
Excellent.

A couple of notes: The IR temperature gun won't give accurate temperature readings at the center vent, though. A better way to monitor those temps continuously, which you'll need to do, is to place the probe of an analog or digital thermometer (with it's dial facing out, of course) into the center vent. As soon as the vent temperature and pressures begin to rise, you'll know that you have just passed the "sweet spot" for the amount of refrigerant the system needs to cool optimally and to stop charging right then.

Be sure to drain the oil out of the new compressor, measure it, refill it with the same amount, and then distribute the remaining oil as discussed earlier.
harryjames001 wrote: Thu Jul 15, 2021 12:08 pm I would like to thank you for taking the time to give me your expert advice and it is very much appreciated. I will let you know how it all goes in the coming days and once it is completed.
We appreciate that. We're all volunteers on this Forum, and we enjoy helping people out as much as we can. We'll look forward to your report.
harryjames001
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Re: 1990 Buick Riviera changing from R12 to R134A

Post by harryjames001 »

Hello John
I finally managed to get the system charged up and running and the inside vent temperature is close to 50 degrees F. My concern is that the gauges, are giving me wrong and conflicting readings. The high side is close to 75 PSI and the low side has been as high as 300 PSI. The gauges are from a cheaper "Box Store" and if I manipulate the control knobs on the quick release adaptors and on the manifold, I can get the readings to reverse themselves and get the low side down to 35 PSI and the high side between 150 degrees F and 225 degrees F. I put in 28 ounces of R134a into the system and dispersed the PAG 46 oil around each component, as you recommended. Could I have faulty gauges or is the orifice tube clogged and not working? Could there be the wrong amount of R134a in the system?
Your comments and advice would be appreciated.
Thank you
Harry
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JohnHere
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Re: 1990 Buick Riviera changing from R12 to R134A

Post by JohnHere »

harryjames001 wrote: Wed Jul 21, 2021 2:21 pm My concern is that the gauges, are giving me wrong and conflicting readings. The high side is close to 75 PSI and the low side has been as high as 300 PSI. The gauges are from a cheaper "Box Store" and if I manipulate the control knobs on the quick release adaptors and on the manifold, I can get the readings to reverse themselves and get the low side down to 35 PSI and the high side between 150 degrees F and 225 degrees F.
I think you meant 150 PSI and 225 PSI. Regardless, whenever testing the high and low system pressures, ensure that both hand-wheels on the Manifold Gauge Set (MGS) are fully closed and that the thumb-wheels on the adapters connected to the vehicle's service ports are fully open. To open them, rotate the thumb-wheels clockwise until they stop. If you still get readings that don't make sense, then the MGS itself is suspect.
harryjames001 wrote: Wed Jul 21, 2021 2:21 pm I put in 28 ounces of R134a into the system and dispersed the PAG 46 oil around each component, as you recommended. Could I have faulty gauges or is the orifice tube clogged and not working? Could there be the wrong amount of R134a in the system?
harryjames001 wrote: Wed Jul 21, 2021 2:21 pm ...the inside vent temperature is close to 50 degrees F.
With a vent temp around 50, it sounds like it might be slightly undercharged yet. Try adding another ounce of refrigerant at a time while watching the vent temp and pressures. You'll need a second person for this. Then allow the system to run for a few minutes to stabilize. If the vent temp drops a little and the pressures stay within the expected range for the ambient temperature, you'll know that you're on the right track. If the vent temp and pressures begin to rise, you'll know that you have just passed the maximum charge and to stop there.

If you already disconnected the MGS from the system and the refrigerant container, you'll need to re-connect them to add more refrigerant. Purging the yellow hose at the MGS will minimize the entrance of unwanted air and moisture into the system. As before, while charging with the engine and compressor running, the red hand-wheel on the high side of the MGS always remains closed.

Open the low-side hand-wheel on the MGS and introduce more refrigerant gas (not liquid) into the low side while monitoring on the scale how much is drawn in. The thumb-wheels on the adapters connected to the vehicle's service ports are both fully open during this procedure. It's very important to ensure that all of this is done correctly before proceeding to add refrigerant.

I think you said that you replaced the OT with a new one. So I doubt that it's clogged. Verify your MGS first, as discussed above.

Measuring the pressures should be done at an engine speed of about 1,800 RPM, compressor/clutch engaged, windows and doors open, A/C on maximum, blower on high, and the under-hood fan(s) operating.
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