Use your words Arby’s. Be helpful, tell him why you want a picture of the can.

 

Are you speaking for him or do you think he is capable of asking for himself if he chooses to? How exactly can I "be helpful" before I see the label?

 

This code is monitored by the HVAC Programmer. Low refrigerant charge (or obstructed orifice tube such as the one shown earlier in this thread) can cause high cycles with short on, long off times. The programmer monitors the number of clutch on/off cycles over a period of time. IIRC, more than 8 in a minute, sets the code. The programmer does not monitor system pressure nor know what the actual charge level is. It deduces that the charge is "low" by monitoring the number of clutch cycles. My point is that there are conditions other than "low charge" that can set 09.

Regarding "overcharge". My experience has been that R134 is more susceptible to 'lack of cooling performance' from overcharge than R12 ever was. Particularly as ambient temperature rises. Industry practice, or at least what I've seen published in various places is to use 90% of the R-12 charge amount when 'converting' to R134. The C4 system specifies 2-1/2 pounds of R12 which is 40 Ounces. 90% of 40 is 36. R134 comes in 12 ounce cans. So exactly 3 cans is the desired charge for R134 in a C4 system.

I return the control of this thread back to arbee.

 

During my training at trade school, it was noted that the requirement for less quantity of R134A vs R12 in a conversion is that R134A is more efficient. Latent heat of vaporization for R134A is 215 kj/kg. For R12, it is 165 kj/kg. Efficiency is defined as output over input. As I have mentioned before, eggheads designed these systems to work as a unit. Since R134A requires more heat per weight measurement to vaporize than R12 does, this means R134A is removing more heat from the cabin than R12 per weight measurement, resulting in less quantity required while operating in the same environment as the one designed for R12.

Dogs - You are 100% correct in that the "low freon" code has no way of knowing what the charge in the system is. Cycling switch controls the compressor,
the high safety switch guards against overpressure and the fan switch controls cooling fans. As you stated, other variables other than low refrigerant can trigger this code.

 

Thank you for the above. I will never remember those actual numbers, but I will always remember that it "is a lot", and helps me understand some things re why the R12 systems react the way they do with R134 in them. I learned something that helps, and I gave a thumbs for it. Thanks.

I have done a zillion r12 to R134. My observations have been that cooling performance in our South Western desert climates where ambients regularly exceed 100F, in 'converted' systems' can be lackluster. Just the way I do it, but I continue to use the white orifice tubes that were used in the R12 system.

My question is simple: Would changing to a smaller orifice than was used with R12 result in lower evaporator temperatures (lower pressure after the orifice) because the increase in efficiency requires less refrigerant through the orifice? I realize that the 'lowest temp' possible is just above icing which must be avoided.

I drive to my place in AZ in July in 115+ F temps. The clutch isn't cycling, and vent outlet temps are in the high 40 - low 50s F. I don't sweat, but it isn't very cold in these ambients. Under these conditions, would a smaller orifice result in cooler vent temps? EDIT/ADD: Although I religiously adhere to, and achieve, the 36oz charge, could the high outlet temps be a result of an 'overcharge' in these elevated ambients? Perhaps just a bit less refrigerant charge would result in an improvement in the 115F desert?

Thanks again.

EDIT/ADD II: I found this chart of orifice tubes. I only see the white .072 for GM. There are other sizes that look like they may work, but the index nu bs are different than the white one. There may not be an alternative. Cheers

 

The absolute biggest detriment to conversions is the condenser and its ability to get rid of heat. As I mentioned, these components are designed as a unit. R134A operates at higher discharge pressure than R12 (as I mentioned in my other thread, think supercharging - higher boost, higher intake air temperatures.) When you are now pushing R134A through a condenser designed for R12, the efficiency goes down. Another reason that some DIYer's complain about lower cooling with their conversion is that they more than likely have introduced what is known as noncondensables into the system (air). These take up room in the condenser and further handicap its ability to waste the heat to the outside. Proper purging of lines and proper evacuation is paramount. As far as the orifice tube goes, I don't (IMO) think this is a major player. Remember, it is not the lower temperature liquid after the orifice tube that cools the air(the lower temperature is simply a result of the lower pressure - Bernoulli's Principal), it is the boiling inside the evaporator that removes the heat. I don't believe .070 or .067 makes that big a difference. The larger the orifice, the better so long as the evaporator can process all the refrigerant. To small an orifice and there is not enough "product" to allow the evaporator to cool to its potential. Even if the orifice is too big, freezing will not occur because the cycling switch will detect the lowering pressure and turn off the compressor. However, that is not desirable because now we are cycling excessively and parts failure (clutch) has a higher degree of probability. My old neighbor was a mechanical engineer and once spoke that the best efficiency of any mechanical component is operating at its designed max output. Most of today's cars run the compressor 100% of the time and adjust the swashplate to control output as needed.

 

That is kind of what I was thinking, I'll just admit I didnt know how best to convey the information though. (Unlike your response, which is more coherent than this gibberish I had written)

My reasoning was bigger orifice = more flow and thus more heat transfer everywhere in the system with supporting air flow on the condenser. I've heard of people resizing orifices for conditions like taxi service where they are stop and go to improve performance... but I agree in that I can't really see it making a huge difference as the transfer across the condenser is going to be the limiting factor due to low air flow...

I used the stock sized white orifice when I converted my 84 to R-134a, but I did install a parallel flow condenser. I do feel that helped compared to the stock tube and fin condenser it would've had otherwise...

 

Parallel flow undoubtedly better for cooling capacity. I have no experience with the following but some who have had compressor failures say you have a chance of flushing a tube condenser. With a parallel flow I have heard you're pretty much fkd - buy a new one. I'm can't attest.

 

Yes. The first condenser I ordered was actually damaged in shipping and the company requested I just cut it up and dispose of it and they replaced it. But in cutting it up, you could see the ports are more like capillaries. I don't know that I'd trust ever being able to get everything out even with a good solvent flush. I do believe it was also tagged to replace in event of compressor failure and to not flush it out.

Edit: I was curious so I pulled my invoice from 5 years ago. At the time the condenser was $78. Cheaper enough I would just replace it. I looked up the same model, $250. Insane what prices have gone to.