Correction: R134a Conversion Question (Sorry)

Greetings, Is it possible for air to blow too cold from the center vent after converting from R-12 to R-134A? I just converted my 1993 Honda Accord. A technician pulled as vacuum for 30', added exactly 28 oz of R-134A (the lower limit of R-12 listed on the under hood plate) & told me that oil would not be necessary because the car was so old that there was probably enough mineral oil impregnated in all the parts to maintain adequate lubrication. He said these conversions could fail immediately, in a week or whenever. There were no guarantees. After a few days & research, I added a can of 2 oz Ester oil with 2 oz R-134A to give some circulating lubrication. Anyway, the vent blows at 40 degrees after a few minutes & then after I turn the fan down, it fluctuates between 30 to 40 degrees (confirmed with 2 different thermometers). Pressures are 35 to 40 PSI low & 230 to 280 PSI high. I thought the system was working great until I found this quote from a technician in an old thread (2002) in response to a poster who had stated that his conversion was blowing ice cold:

"Then its too cold....no system puts out air at 32F and is working normally, unless its a refrigeration unit..:) That would mean, the system is UNDERCHARGED....look at any refrigerant temp/pressure chart."

He was attacking the credibility of the original poster, who seemed knowledgeable but abrasive.

My understanding that overcharging with R-134A when converting was the most common error. Based on my pressures & temperature results, is my system undercharged? Is there something wrong with mys system to be blowing cold air. It seems to be working great. Thanks, Rich

Reply to
richrx
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You probably should check your thermometer (mix up a cup of crushed ice and water and dunk the problem in it to make sure it is close to correct). Hondas use an expansion valve with a thermostatic probe. You probably need to replace the R12 valve with one intended for R134. I also think you have too much R134 in the system. Most of the guidelines I see say to use 65% to 75% as much R134 as was specified for R12 when doing the conversion. I've had three systems converted to R134 (two in farm tractors) and all worked fine. In fact, the last one converted works better than when new.

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Ed

Reply to
C. E. White

Thank you for responding. I confirmed the temperatures with a new thermometer. Maybe I will drop both of them in ice water to verify. As far as it being over-charged, I read on some site that a rule of thumb method when converting was to stick a thermometer in the vent, add R-134A slowly while the temperature drops. When the temperature starts going up again, they advise to remove the amount of R-134A added after the temperature hit its lowest. I would expect warmer vent temperatures & higher pressures if I was over-charged. Also, when the tech checked out my system with an electronic leak detector, a "medium" leak was detected around the compressor mounting so any state of over-charging will self-correct itself. I was actually interested in confirmation of the statement that an undercharged R-134A system would produce a "too cold" situation. It seems counter intuitive. Rich

Reply to
richrx

There are so many disturbing things about this conversion that I don't know where to start.

First of all, "the parts are impregnated with enough mineral oil to protect them" is absurd. By that theory, you should be able to drain all the oil out of your engine and never re-fill it after 50,000 miles, because "its got enough oil impregnated into it to protect it."

Second, adding a couple of ounces of ester oil and hoping for the best is asinine. There is now (potentially) too much inert matter (oil) in the system for it to work right, let alone last long. The ONLY way to achieve a successful conversion is to completely drain the system of all oil, FLUSH the evaporator and condensor and hoses with a solvent (but NOT the compressor! just pour the old oil out if it), and then add the correct amount of PAG or POE (aka "ester") oil for the system. The oil charge for R134a is the same as it would be for R-12. You also need a new receiver/drier whenever the system has been opened and flushed. Replacing the drier is even more important with R-134a than with R12 because R-134a oils absorb water so easily, much like brake fluid does.

Third, the "rule of thmb" quoted above about slowly adding R-134 and watching a thermometer is asinine. The ONLY correct way to charge a conversion is to use 75 precent (by weight) of the recommended R-12 charge.

Fourth, whether or not an undercharge causes a "too cold" problem at the vents depends on the design of the system. Is the thermostatic clutch cycling switch located in the evaporator core? If so, then NO it won't blow too cold. Is the switch located on the suction line under the hood? If so, then MAYBE it will blow too cold becuse there's not enough cooling potential left after the evaporator to cool down the suction line.

All in all, I'd say this conversion is marginal at best, disastrous at worst. It is very possible and practical to convert older systems and have them perform very well and last a very long time. I've converted two 1960s systems of my own, and they've both performed extremely well. But you can't scrimp- its not a simple thing to do, and saving $$ by skipping steps like flushing out the old mineral oil is a false economy. You run the risk of having the oil block the expansion valve causing a cooling loss (at best) or having the compressor suck in a big slug of un-dissolved mineral oil and break a piston or a valve (at worst). And no matter what, the presence of the mineral oil that is not soluble in R-134a will decrease the effectiveness of the soluble PAG or POE oil because some of the PAG or POE will try to mix with the mineral oil and fall out of circulation, rather than staying dissolved in the refrigerant and circulating through the system..

Reply to
Steve

Thank you for responding. All your points are well taken & previously encountered during my research of this subject. My compressor(14 years old) had a slight shaft oil leak & the aforementioned medium (so far the charge has lasted 10 days) Freon leak at the mounting base/bolts. The initial diagnosis by the independent tech was that all I needed was a recharge with R-12 which is readily available at a reasonable price not far from where I live (Arizona) Inasmuch as the local Honda dealer had recommended a new compressor ($1800) & I did not want to damage the ozone layer by just throwing R-12 into a leaky system, I opted to do a simple retrofit to last the possible short, existing life of the compressor. However, I have a couple of asinine follow-up questions. Approximately what percentage of the lubricant resides in the compressor? Does all the oil in the compressor immediately migrate from the compressor & circulate when the compressor is on? Or does some of the oil always remain in the compressor? If so, does any of that resident oil passively offer lubrication to the compressor through simple mechanical action of the compressor? By the way, I became asinine when I read the following on the Interdynamics site:

"Do I need to remove the oil that's in the system? Is the old oil compatible with the new oil?

No. The residual mineral oil left behind after you evacuate a R-12 system will not mix with the new R-134a refrigerant. That is why we add Ester Oil, because it will mix with R-134a, lubricate the system components and is compatible with the residual Mineral oil..."

Their kit would have added approximately 7 to 8.5 oz of Esther oil depending on whether I used pre-mixed R-134A or added the recommended amount separately. So, I chose the safe first step of being 23 to 28% as asinine as Interdynamics by adding only 2 oz of Esther oil. Furthermore, also from the Interdynamics site, this is what I was planning to do:

"...The mineral oil just collects in a low place in the system (such as the accumulator), where it stays, UNTIL IT IS REMOVED AT SOME LATER DATE DURING FUTURE MAINTENANCE OR REPAIR (my emphasis). The mineral oil does no good, but it does no harm either. It's just there."

Thank you, Rich

Reply to
Rich

Rich wrote in news:Pa8wi.111375$ snipped-for-privacy@newsfe12.phx:

that is not necessarly true as oil has been know to pool in a poor spot and restrict flow where it shouldn`t. KB

Reply to
Kevin Bottorff

However, I have a couple of asinine follow-up questions.

Actually that's NOT a simple question. It depends not only on the type of compressor (some have large oil sumps that tend to retain a fair amount of oil, some don't, some have oil cirulating pumps, some don't), but also on how the system is operating. When the system first kicks on, the oil in the suction side plumbing (everything between the expansion valve and the suction inlet of the compressor, including the evaporator) foams up like whipped cream as it is subjected to vacuum and all the refrigerant that is dissolved in it flahes to gas. When that happens, it passes through the compressor and some will accumulate in the sump (if so equipped), but some will also go right through and get into the discharge side, where it slowly works its way back around. In general, the oil goes nuts for the first few seconds after the system cycles on, and then tends to stabilize with a certain fraction in the compressor sump and oil circulation system, and the rest distributed and circulating with refrigerant. When measuring the oil in a system, you are supposed to operate it for 5-10 minutes at high idle and high fan speed (max load on the A/C) to stabilize the distribution of the oil. Of course, you generally only DO that if the system is broken, in which case you can't run it... but I digress. Lots and lots of really short-cyling can be very hard on the compressor because that tends to put ALL of its oil out in the refrigerant stream, but that's not usually a problem with car A/C systems as much as home systems where there's a long run of plumbing between the compressor unit and the air handler.

Interdynamics .... oh joy. :-p

But it takes up space that the engineers who DESIGNED the system intended to be occupied by refrigerant.... not oil. It does have negative effects, and if a good bump in the road causes a slug of it to fly into the suction side of the compressor, the effects can be sudden, loud, and destructive :-p

Reply to
Steve

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