A/C Pressure Questions

[dpuckett]

I have tried the search function, and have not found a satisfactory answer. What suction side pressure should one shoot for when recharging the AC system with HC12a? The FSM says 22-39psig of R12 on a 90 deg day (has been averaging a hair more here, but closer to 90 than 100). Should I just shoot for the middle, and call it good? Or is there some magic number you pros strive for?



ALso, what kind of oil needs to go into the Sanden SD709 compressor? I plan to get it completely evacuated by my g/f's shop (one time that the tools would cost more than having them do it), and do the recharge myself, since like most automotive shops, they dont recognize the HC12a replacement.



Daniel

 

[sdstriper]

Here's a pressure/temperature chart



http://www.autoacforum.com/aacf/ptchart.cfm



What oil is HC12a compatable with? The oil capacity if the SD709 is 7. 25 ounces IIRC.



The FAQ for AC;



Automotive AC Information Forum - ACKITS. COM

 

[KOG]

HC12 is compatible with oil. Any oil. You normally go for 35-37lbs low side pressure with engine running at 1500-1200rpm. You can put 25% of the normal charge into the system and then add additional charge SLOWLY at it takes time for the system to stabilize and you do NOT want to overcharge.

 

[dpuckett]

Thanks, guys. I'll get on it as soon as I get the truck back. Now driving Mom's truck so I can troubelshoot and fix her speedometer.



DP

 

[RWWinslow]

Use the same oil as originally supplied. Oil compatibility issues can get prety sticky (sorry about the pun - couldn't resist) Keep us posted on how the HC12a works - our A/C tech at work really likes the stuff. . . it can also be added as a topping charge - but it will cross contaminate the R12 in the system.

 

[dpuckett]

The FSM calls for a "500 SUS viscocity wax free refrigerant oil. " Can someone please translate this to normal oil? The amount is 4. 6oz, FWIW.



I'll keep y'all updated- Mom's truck was converted to 134A several years ago, and it is mediocre at best, we both have club cabs (though I have tinted rear windows) so I have a close comparison.



DP

 

[RWWinslow]

Ester or a PAG refrigerant oil - I believe that PAG was the original fill oil for this compressor and R12. Ester and PAG may or may not be compatible. . . . you will have to do some digging -- my memory is not that good and my notes on this subject are currently packed away. PM or Call if you need additional help.

 

[sdstriper]

The FSM calls for a "500 SUS viscocity wax free refrigerant oil. " Can someone please translate this to normal oil? The amount is 4. 6oz, FWIW.



I'll keep y'all updated- Mom's truck was converted to 134A several years ago, and it is mediocre at best, we both have club cabs (though I have tinted rear windows) so I have a close comparison.



DP

SUS = Saybolt Uniform Seconds. As stated in the Compressor Service section further along in the manual...



Not very helpful I'm sure! Although I believe it is a mineral oil, and the other is synthetic. Non-compatable with r12 from what I understand.

 

[RWWinslow]

Ester's and PAG's are both synthetics and are wax free. Wax free generally means no mineral oil / synthetic.

 

[sdstriper]

I am certainly no expert but I have read that r12 and PAG oils are not good for your a/c system. The chlorine contained in r12 or other chlorinated compounds can react with the PAG and cause lubrication degradation.



From this site,



Arizona Mobile Air Inc. (ACKits.com): PAG - BVA Auto 100 - Mineral Compressor Oil



"525 SUS Viscosity) Mineral oil developed for use in General Motors automotive air-conditioning systems. Soon became the industry standard for all automotive manufacturers. Mineral is for use in automotive systems using R-12 refrigerants. Not for use with MP-52 or R-134A. "

 

[Greenleaf]

R12a is compatable with any oil. Shoot for low pressure. You don't need much. About 12 oz will do you. I have about 20 psi on the suction side (with the compressor operating about 1200 rpm)



The system holds about 41 oz of CFC 12 so that is 14oz of HC 12a. Low is good. Too much coolant and it will not operate proper. (flood the evap)The manual you recieve with the HC12a will ask you to shoot for 28-38 psi



GL

 

[dpuckett]

I should have PMed Greenleaf from the get-go, but I figured someone somewhere may benefit from my ignorance. 20-22psi it is (FSM says 22-39); along with whatever oil the compressor came with, lest there be traces of it after I get it evacuated. How does one go about adding it? Or do I just go buy a can of oil and add it through the low pressure port?



DP

 

[RGramlow]

evacuating the system won't usually suck much oil out of it. I always thought that only mineral oil was to be used with R12. If you think you need to add oil it will be hard if you plan on having them evac and you recharge. You should have opened a line adn added it before taking it in. I don't have the big fancy machine to inject oil with the refrigerant, so what I do if I have a leak and lost alot of oil I try to keep an empty can on my can tap and punch a hole in the bottom of it and pour a few ounces of oil in after evacuating while still under vac I hold the can upside down and open the valve and the vacuum will suck the oil from the can into the system, but close it right away when you hear it go empty to keep air out, then recharge as normal. If that is suppose to be a direct replacement for R12 then just add the amount that is called for for the pickups a/c system and don't worry about the pressures.

 

[Greenleaf]

The cans of HC12a have oil in them, just like most of the other's.



I too find that when the system is evacuated, the oil remains. I doubt you will need to mess with the oil. It will still have oil and the new cans will contain oil , so... ... ... ... .



When I installed a new compressor, it had oil in it and the new coolant had oil, so I never messed with oil.

 

[KOG]

HC12 is NOT a DIRECT replacement for R12 in the sense of weight. It normally takes about 1/3 the amount by weight, but it must be charged by pressure. It's a superior refrigerant in terms of efficiency and oil retention/lubrication, but cannot be charged the same way.

 

[Greenleaf]

Thank you for mentioning that. I was going to attempt to clearify the fact that HC12a is NOT CFC-R12 but I most generally "step on toes" when I do.



Sorry and thank-you. Some seem to think he is installing the OEM coolant/chemical R12.

 

[dpuckett]

Update:

I finally got the stuff bought (3 cans of Duracool), bought and installed a new drier, got the system evacuated (supposedly, more on that in a moment), and added the Duracool. I filled it to 25psi at idle on the suction side (it's 100 deg today, so added a few psi to the count; it only took one 6oz can to get there, too). The vents are blowing cool air at best, more like luke warm. It was better with the R134A, to be honest. I am not impressed. But, I did notice that when I was unhooking the high pressure fitting, there was some green goo that came out in the 1/2 second "Phsshhhtt". Kinda resembled the tracer dye, but was different- didnt glow. I did it a couple more times, and ended up with a bunch of stuff that was the consistency of mayonaise, and army green. What is going on here? I am thinking this stuff is causing my temp issues.



I was under the impression that when the system was evacuated, the gunk, contaminants, moisture, air, everything (within reason), was pulled out. Am I missing something? G/F's shop didnt do it, she made the appointment with another shop they sometimes sublet through. If it is quality similar to the front end "alignment" I got, I am going to be VERY peeved.



Pressures were 25psi low; 150psi high side at idle.



Thanks for all the help and advice so far.



DP

 

[KOG]

25 is a little low. Probably need more gas. When you get HC12 charged correctly it WILL cool better than 134 or R12. Wednesday we had one of the G. Carvans putting 55 degree air out of the vents when it was 106 with high humidity outside. The CTD runs around 55-60 degrees from the vents when it's 105 with high humidity if driving, about 70 at idle.

 

[B.G. Smith]

Quote

("I was under the impression that when the system was evacuated, the gunk, contaminants, moisture, air, everything (within reason), was pulled out. Am I missing something? G/F's shop didnt do it, she made the appointment with another shop they sometimes sublet through. If it is quality similar to the front end "alignment" I got, I am going to be VERY peeved. ") -------------------

Sounds like you have some oil still in the system that is not compatible with the new refrigerant. When you "evacuate" the system. only the air and any chemicals/or whatevers that will evaporate at low pressures are removed. The only way you will get any oil when evacuating is if the system still has refrigerant in it when you start the evacuation and the oil/refrigerant mixture will foam causing oil to be removed. To remove oil from a system you would either have to remove each component and drain it (Impossible with the receiver drier) or flush it out with a liquid that will mix with the oil and carry it out and the residue can be remove by later evacuation like Freon 11. (I don't know if F-11 will mix with the oil you have in your system. ). Oil charges for different refrigerants are available in ppressurized cans so thay can be added after evacuation. Refrigerant does not contain oil in the can. In most systems, a lot of the oil is entrained in the gas/liquid stream. Too much oil will degrade the cooling capacity, to little and there goes the compressor.

 

[dpuckett]

Thanks for the evac explanation, B. G. Smith. That settles my nerves a little.



It looks like I may need to try adding just a little at a time, noting the pressure, ambient temp, etc, and trying it out for a little while, huh? I have a doo-hickie that screws onto the can, and will seal it off when I turn the valve off. It also sounds like there could be too much oil in the system. I have no idea what the previous owner(s) did to the AC system, only that I needed it in January in Houston.



I'll report back. Thanks, guys.



Daniel