A/C Needs R-12

[btoscano]

My 1990 3/4 ton is low on Freon. I have everything I need to recharge it, but am wondering if I should replace the A/C O-rings to eliminate slow leaks, etc. Is this advised? (I searched didn't find anything about o-rings). What's the best place to get a set of o-rings?



Thanks,

 

[Philip]

Any good parts store should have them in stock. The bad news is they might have to match them up by size which means that you need the old ones out to get the replacements.



Rather than discharge the system and do all the o-rings. Put a can of die into the system and see if it shows any leaks.

 

[btoscano]

I should have said really low The charge is low enough the compressor won't come on. Can I charge it up with some nitrogen and add colored die to that? Would that work to find leaks?



Thanks,

 

[Philip]

Can I charge it up with some nitrogen

Good question. I have no idea if you could do it. I have never heard of it being done before.



I would try to bypass the low pressure switch myself then put enough R12 in to get it working and then add the die.

 

[Paul Herioux]

Nitrogen for checking for leaks

I use nitrogen at the shop to check for A/C system leaks. To use it the system needs to be recovered first so there is no refrigerent in it. I them pressurize the system to about 250lbs. Any severe leaks will be audible if you are in a relitively quite shop. To find the small leaks I spray all the accessible parts of the system down with soapy water, wait a minute of two and check for bubbles. The warmer the climate, the higher you soap level needs to be to prevent evaporation. Do not run the system with nitrogen in it. The lubrication oil in the A/C system will not dissolve into the nitrogen like it does in refrigerant. Running the system will cause compressor damage due to lack of lubrication. It will also cause extremely high pressures (400+ psi). This will cause the high pressure relief valve to blow and possibly rupture hoses. For the really tough leaks I charge the system and add a flourecent dye. The only brand I have found that works really well is made by Tracerlite and should be available at most parts stores. An oil injector is needed to add it to the system. This dye shows up under a black light and will be a bright yellow. It is a dull green in natural light. The best black light source I have found is the cheap 12" single tube flourecent lights they sell at Walmart for about $18. Only drawback is that they are easy to break in a shop enviroment. Of course I can buy a lot of these lights for the cost of the bulb for the light we have at the shop-$104 :--) each!!



sorry to go so long, hope it helps,

Paul

 

[btoscano]

Thanks for the soap bubble idea. When adding the nitrogen to the system, do I add to the high or low pressure side, or both?

 

[Paul Herioux]

Which side you hook up to depends only on what you have for fittings on your tank. My current setup at the shop hooks to the low side for R-12 systems and the high side for R-134a systems. You are only building a static pressure in the system, it will be equal at all points in the system. If I had my preferance I would fill from the high side as this most closely duplicates normal flow through the system during fill. Once pressure is stabilized all flow has stopped so it doesn't make a difference.

HTH,

Paul

 

[btoscano]

Paul,



I hooked up my R-12 manifold supply line to the nitrogen tank and let in about 55 psi to the low side and 125 psi to the high side. Over the next minutes the low and high pressure sides came within 10-15 psi of one another. No audible hissing and no loss of pressure over about 15-20 minutes according to the guages, nitrogen cylinder removed. I guess this is pretty good? Should I try both sides at 250 psi and see how it goes from there?



On another issue, flushing the A/C system in my 1987 Mercedes to convert from R134a back to R12. I have removed the expansion valve and am running a FJC flush thru an air gun. At first green came out, then just the flush color. I plan to run some nitrogen thru there to dry it out. I will use an R12 manifold hose, condensor from a parts car. I am using a new expansion valve and drier. I would like to use the switches from the parts car. The compressor has R134a oil in it (Nippondenso compressor) and I'm told that adding mineral oil and turning it over to let hte oil drian out repeatedly is the best way to convert the oil in the compressor. Do you see any pitfalls with this technique? i will then pull vacuum for 30-90 minutes (which do you prefer) and add R-12.



your comments appreciated. This is my first A/C work and I appreciate the comments from someone with lots of experience.



Brian Toscano

 

[Paul Herioux]

"I hooked up my R-12 manifold supply line to the nitrogen tank and let in about 55 psi to the low side and 125 psi to the high side. Over the next minutes the low and high pressure sides came within 10-15 psi of one another. No audible hissing and no loss of pressure over about 15-20 minutes according to the guages, nitrogen cylinder removed. I guess this is pretty good? Should I try both sides at 250 psi and see how it goes from there?"



I would double check it with 200psi if it were mine just to make sure. Sounds like it should be ok though. The 15 minutes with no pressure drop was a good sign.



"The compressor has R134a oil in it (Nippondenso compressor) and I'm told that adding mineral oil and turning it over to let hte oil drian out repeatedly is the best way to convert the oil in the compressor. "



That is the way I do it. Time consuming but very effective.



"i will then pull vacuum for 30-90 minutes (which do you prefer) and add R-12. "



Sounds like the system has been open for a couple of days. Start the clock when the low side gauge gets to 28 in. hg. and go for one hour longer. Gauge should get to 30 in. hg. by this time if you have a good vacuum pump. Some of the cheaper ones will only get to 28. 5-29 in. hg. After the hour is up close the valves on gauge set and let sit for 2 minutes. Gauges should move. If the pressure climbs immediately after closing valve you have a leak. If it drops steadily to about 21 in. hg. in the two minutes you either have a very small leak or have some moisture left in the system which needs to be boiled off. In this case vacuum for an additional 30 minutes.



Sounds like you are going in the right direction Brian, keep up the good work.



Later,

Paul

 

[btoscano]

Paul thanks for the advise. It will be 3-4 days before I get the rest of these tasks completed. The system was opened in Feb. when a deer took out the condensor and a bunch of other parts. I taped everything to try to prevent moisture from entering the system. It took so long because I swapped engine and trans and then had to deal with some suspension issues. I've turned the clutch by hand a few times 1-2 months ago and the compressor still spins freely. How does this extended time play into fixing the system?



Thanks,

Brian

 

[jerrethomas]

just make sure you flush the system good before you pull it in to a vacuum. when your done flushing it, the vacuum pump will boil pretty much all the moisture out of the system. moisture will boil at a much lower temature in a vaccum.

 

[btoscano]

This weekend I reinstalled the components of the Mercedes A/C and ran the vac pump on the truck.



I put 275 psi of Nitrogen into the Mercedes and it held it. Then I put the vac pump on it. Only got to 27. 5. Did that for about 30 minutes and then drove for 30 minutes to warm up the engine. Came back and put the guages on, it was 26-27. I think it may have lost 1 in Hg by connecting the guages, etc. Ran the pump again, and it got back to 27. 5 and stayed there.



I borrowed this vac pump from a mechanic who doesn't really use it anymore. I asked him if he ever changed the oil in it. "No. " was his reponse. I'm going to run it with his guages and see what readings he gets. He claims more inHg than I am getting.



In the truck, it pulls 26 in Hg and disconnecting the pump & I loose vacuum relatively quickly, so I need to find that leak.



When I charge with R-12 is it Okay to turn the cans upside down and add as a liquid? Or should I try to heat up the can and let it go int as a gas?



Thank,

 

[JBlock]

Turn it over

As I recall the last time i need a charge was on my 1967 mustang in college when I added air, I think the instruction on the can said to turn it over, but I not positive.

 

[Paul Herioux]

"When I charge with R-12 is it Okay to turn the cans upside down and add as a liquid? Or should I try to heat up the can and let it go int as a gas?"





Charge as a gas. Charging as a liquid can be dangerous for the compressor because the liquid won't compress and will cause damage to the valves in the compressor. The only time I charge as a liquid is when using a charging station with a pump. I push the charge in through the high side before I start the system. When charging with cans you have to charge from the low side using the A/C compressor to suck the refrigerant out of the can. When using cans I normally fill a bucket with hot water and partially submerge the can. Makes it go a lot quicker.



An oil change in your friends compressor should help. I change the oil in the shop's compressor on 15 hour intervals on average. The machine calls for a 10 hour interval but finding time to do it when the shop is busy just doesn't work some times. I really notice a performance change when it gets up around the 20 hour range.



Got to go to work.

Later,

Paul