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Oil Choice for a R12 / R-134a mix match system???

JetMechanic2242 on Wed May 01, 2013 8:00 PM User is offlineView users profile

Year: 1984
Make: Chevy
Model: Suburban
Engine Size: 6.5 TD
Refrigerant Type: R12
Ambient Temp: AZ Hot
Country of Origin: United States

I have been pulling my hair out ... researching which oil to use in a system that is mixed. The system is mainly a R-12 dual evap core system with one orifice tube and one expansion valve as came on the 1984 Chevy Suburban. The R-134a compressor (HT6 model) and hose assembly as came on the 1997 Chevy 6.5 Turbo Diesel P/U engine that was transplanted into the Suburban body. My reading indicates that the 1997 Chevy P/U engine requires 8 oz of PAG 150 oil with the R-134a charge for a single evap core system. A 84 Suburban with only front A/C get 8 oz of mineral oil with R-12 and the dual (front / rear) a/c gets 11 oz mineral oil with R-12. Good so far.

Before you point out that R-134a will work here... let me say it isn't the same. The engine has been in for 3 years and I have never been happy at 110 F in Phoenix with the R-134a in the system. Yes, it has been properly evacuated and charged. (Every summer since install, trying to tweak it a little more). The R-12 system worked great in the Arizona summer for many years without any trouble until the engine swap when it was recovered to go to the R-134a. Have heard many identical stories on stock Suburban's that have been converted to R-134a.

Before it gets really hot I will tear down the system install a new condenser core (parallel flow) with two new evap cores (front / rear), a severe duty variable orifice tube (4 Seasons # 38904), new expansion valve, new accumulator, drain and flush new oil in the compressor, flush the lines with A/C flush, and install all new seals with the intent to have the system charged with R-12.

Question: Should I choose the 150 viscosity mineral oil for the R-12 in the system and how will it react in my 1997 Chevy HT6 compressor? As good a lubricant as the original PAG 150 oil? GM used I think single end capped PAG in 1997. Or should I go to the DOUBLE END CAPPED PAG 150 oil and hope that 5 years from now the R-12 doesn't begin to break down that type of PAG and eat my system. I have read that the double end capped PAG is compatible but not necessarily recommended for R-12.

Question: On a side note: what do people think of the a severe duty variable orifice tube that 4 Seasons makes? Part Number: 38904. Or should I opt for the orange color stock orifice tube? I already bought the variable one...

I am looking for guidance ... So what are your thoughts and Why?

What goes bump when you're driving down I-10 is different than what goes bump at 35,000 feet! No place to pull over ...

mk378 on Wed May 01, 2013 11:06 PM User is offline

Single end capped PAG mixed with R-12 will turn to sludge almost immediately. You have to get ALL of it out of any parts that you're going to use with R-12. Mineral oil is OK in new parts. With engine swaps you need to be sure the condenser airflow is the most it can be-- proper fan shroud, block the sides of the stack, good fan rpm, etc. Forget the variable OT, it doesn't work.

TRB on Wed May 01, 2013 11:38 PM User is offlineView users profile

BVA Auto Glo (POE)


When considering your next auto A/C purchase, please consider the site that supports you:

Edited: Wed May 01, 2013 at 11:39 PM by TRB

JetMechanic2242 on Thu May 02, 2013 4:06 AM User is offlineView users profile

Mk378, thanks for the info.

Yes, I agree system must be clean and I will put extra effort in to making it super clean. Really only the hoses to clean and the compressor to flush with fresh oil since the rest of the system will be new. Three years ago the compressor and hoses were replaced with new to prevent failure of the 26 year old hoses and an unknown wreaking yard compressor.

The radiator is new and the core support opened up for better air flow to the radiator with side rails and fan shroud to the factory t-stat fan clutch and fan for the 1997 6.5 TD (well sealed). There are two aux electric fans and may add two more this time for traffic idling air flow? Will depend on how much time I have when I get into this project this time.

I was already leaning towards nixing the variable OT. Thanks for confirming.

Any thoughts about how the 150 viscosity mineral oil will work in the HT6 compressor? Still not sure how the lubricative properties compare to the original PAG???

What goes bump when you're driving down I-10 is different than what goes bump at 35,000 feet! No place to pull over ...

HECAT on Thu May 02, 2013 9:04 AM User is offline

Assuming the 84 stock tube and fin style condenser is being used; this is most probably why the 134a cooling is marginal. I went thru this with a 90 model dual evap Suburban I owned. If you are now going to install a parallel flow condenser the 134a performance will be much better. If you are wanting to return to R12; no need to change any components. PAG with R12 is not good. Mineral or POE will work with R12, and the POE is actually capable of working with either. The later model components will work with any of the oils.


HECAT: You support the Forum when you consider for your a/c parts.


iceman2555 on Thu May 02, 2013 9:17 AM User is offlineView users profile

Clean the system and use 525 SUS mineral lube. This is the standard for R12 systems and the "H" will work great with this lubricant. Insure the system is fully recharged to insure correct lubricant migration thru out the system. Stay with the correct orifice tube...the standard GM orifice should work well.

The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
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NickD on Thu May 02, 2013 11:38 AM User is offline

One day, R-12, the next day, R-134a, no fault of the consumers, we were really hit when the next day asbestos was banned, force into a major recall. Bit for some strange reason, the manufacturers were held free of this liability, fell completely to the consumers.

Can still buy R-12, but up to one hundred times the cost. GM announced they would provide proper information as to how to convert, but then said, this is too complicated, figure this out for yourself. Ford, for a brief amount of time, offered a complete firewall forward conversion kit, but all at retail prices.

Leaded gas was a real threat to health, no arguments against that, but was given a twenty year phase out. Well not quite, at the end the lead content was only about 10% and would still burn out exhaust valves. With some pre-72 cars, was able to get an intake manifold with an EGR valve in it to safely used unleaded gas when I could walk into a wrecking yard and remove it myself. In Wisconsin, can't even to that anymore.

R-12 was just a theory based on a sealed container exposed to UV light, fist NASA joined the crowd, then backed off with wind currents affecting the ozone layer over the Antarctic. From more intelligent sources, CFC's are fully biodegradable, but the law still holds in effect.

R-134a put a lot more work into AC servicing, that PAG just can't handle any moisture and any servicing to be done correctly requires a full flush, a new dryer, and drawing an extra long vacuum. Now R-134a is causing global warming, no longer friendly. But since you could buy it freely from X-Mart, many were topping off their R-12 systems with it that drastically increased the operating pressures with far less reduced cooling.

If this isn't enough, been told all my life, alcohol and gas doesn't mix, it literally still doesn't, but guess what the government is doing now? Oh, and for years, the EPA has been vehemently opposed to using any forms of HC's in MVAC systems, guess what? Could still be lead in the gas, don't blame them, makes some people with a poorer blood brain barrier, aggressive, extremely arrogant, and very stupid.

Is it time to quit?

Edited: Thu May 02, 2013 at 11:48 AM by NickD

JetMechanic2242 on Fri May 03, 2013 9:09 AM User is offlineView users profile

What goes bump when you're driving down I-10 is different than what goes bump at 35,000 feet! No place to pull over ...

JetMechanic2242 on Fri May 03, 2013 9:50 AM User is offlineView users profile

Looks like the consensus is with mineral oil (500 SUS on this site) for R-12.

HECAT I will go to a true parallel flow type condenser just having a little difficulty with finding a core that isn't physically smaller than my current condenser. I do understand the efficency improvements but fail to see the reason for down sizing ??? Seems the aftermarket P-flow's are smaller if you're not watching the fine print by 10 to 15%. Will be checking dimensions before ordering, if anything will oversize with the idea that some day I wont be able to find R-12.

That was the second (and unspoken) reason I asked about double end capped PAG with R-12. My reading seemed to indicate that it IS compatible with CFC based R-12. On the other hand several web sites do not recommend it's use. Seems like this might be a better choice if eventually we will all be on R-134a or the next new thing as NickD has pointed out.

Iceman2555 I have seen your Georgia Bull Dog on many posts. Lots of good info. Thanks.

What goes bump when you're driving down I-10 is different than what goes bump at 35,000 feet! No place to pull over ...

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