Automotive Air Conditioning Information Forum

PromiseRing wrote:I had vacuumed the system for about 1 hour or maybe 1.5 hours with a vacuum pump I rented from AutoZone. This is the same type I’ve rented there many times before and have always been able to achieve 29-almost 30 in Hg on other vehicles (Including her Toyota, before the new system). Considering I had removed every single possible connection in the system, the likelihood of a leak is higher. When I vacuumed it for 1-1.5 hours, it was 10pm and she was leaving the next morning for the airport, so I was in a hurry to get some refrigerant in the system.

It could be that the pump you rented this time was inadequate. Or, you might have had a leak somewhere in your manifold gauge set hook-ups. A small system leak is also a possibility.

PromiseRing wrote:If she reports back that the ac stopped working, I can only assume it’s because of a slow leak. Now that I think about it though, since the system was open for a few hours, isn’t it much more difficult to get that 29-30 in Hg? On a system that hasn’t been exposed to outside air, it seems to go into vacuum much easier. I’m wondering if I did a longer vacuum and achieved that number, if vent temps would be cooler.

Hopefully not, but let us know whether it stops cooling.

Non-condensable gases (air and moisture) in the system will affect cooling. How much depends on the amount. Less than one percent probably won't be noticeable.

I don't think it makes much difference whether the system has been open for a while. A good vacuum pump should pull down to 29 InHg or better almost immediately. It's just that you have to maintain that level of vacuum for at least 30 minutes to boil-off all the air and moisture. I like to evacuate for one hour or more, as you did. Sometimes, you'll have a bit of internal out-gassing in a well-sealed system that will cause the vacuum reading to drop a little after the initial evacuation. But achieving only 26 InHg on the first attempt indicates a problem someplace. If you have significant non-condensables in the system due to inadequate evacuation, cooling will be compromised to some extent as already mentioned. A system running with significant non-condensables will usually have higher than normal high-side pressures even though airflow over the condenser is sufficient.

On this system, it sounds like the airflow is as good as it's going to get.

Thanks John. I texted my neighbor this morning and she said the AC still in fact is working, although still not as cold as it should be. I want to assume the system is now reliable (even if I’m a hair low on oil... )

I have been 2 hours away at school for the past few weeks so I haven’t touched it. Next time I’m in town I’d like to rent a higher CFM vacuum pump and give that a shot. I think that some people rent those pumps from AutoZone, use them improperly (causing oil to spill) and then they run them while low or out of oil. This obviously causes irreparable damage to the pump.

If I’m able to pull a better vacuum on the system and boil out the remaining incondensibles, I think that will help. If it does not help, I’m not sure of the next step.

As a side note, my father just bought a ~2003 pop up camper of some sort with INOP AC. Compressor comes on and gets hot but it does not blow cold. It’s an r22 system without service ports. We ordered a bullet piercing valve and plan to evacuate and charge with r134a. I understand this is not ideal due to the incompatibility of oils/refrigerants, but as of now he’s not worried about it. He will use it until it stops blowing cold and then just replace the entire system as a whole. I’ll let you know how my experience with that system goes! Haha

PromiseRing wrote: I think that some people rent those pumps from AutoZone, use them improperly (causing oil to spill) and then they run them while low or out of oil. This obviously causes irreparable damage to the pump.

Last year, I was 100 miles from my own vacuum pump. I got the free loaner vacuum pump from local Autozone to use, it was very good.

Cusser wrote:

PromiseRing wrote: I think that some people rent those pumps from AutoZone, use them improperly (causing oil to spill) and then they run them while low or out of oil. This obviously causes irreparable damage to the pump.

Last year, I was 100 miles from my own vacuum pump. I got the free loaner vacuum pump from local Autozone to use, it was very good.

I have had good luck with them as well sometimes. I’ve even used one that appeared new.

I think the issue is, and I could be wrong, people try to vacuum a system that is under pressure already. This forces the oil out of the vacuum pump. IIRC, they should 'properly' evacuate the system to 0psi/0inHg, and then vacuum the system down.

Again, I could be wrong, but this has served me the best results.

PromiseRing wrote:Thanks John. I texted my neighbor this morning and she said the AC still in fact is working, although still not as cold as it should be. I want to assume the system is now reliable (even if I’m a hair low on oil... )

Good news that the system is still working, although not as cool as she would like. Hopefully, that means everything is well sealed and no refrigerant leaked out since last you charged it. As for the oil amount, it'll probably be okay the way it is. But if you evacuate and recharge it again, you could add another ounce or so at that time. I would replace the receiver/dryer again as well since the desiccant might now be full of moisture. They're cheap insurance.

As for the vent temp, I suggest getting hold of a good digital thermometer and secure it in the center vent with a couple of those small gluing clamps available at the home centers so that she can monitor the temperature as she drives. It might actually be cooler than she thinks. I've tried them all, but I like this one best: https://www.thermoworks.com/RT301WA It's intended for gauging food temperatures, but I found that it works perfectly for monitoring A/C vent temps, too. Nice big numerals, very accurate, and it stays on for one hour before it shuts itself off to save battery power. Well worth the minimal cost, I think.

PromiseRing wrote:If I’m able to pull a better vacuum on the system and boil out the remaining incondensibles, I think that will help. If it does not help, I’m not sure of the next step.

I'd go for another evacuation first. If there aren't any system leaks (and there don't appear to be any now), a good vacuum pump should be able to pull it down to at least 29 InHg without any trouble. Never having used one, I can't vouch for the AutoZone rental units. But Cusser has had good luck with them, as he said. And hopefully you will, too.

PromiseRing wrote:As a side note, my father just bought a ~2003 pop up camper of some sort with INOP AC. Compressor comes on and gets hot but it does not blow cold. It’s an r22 system without service ports. We ordered a bullet piercing valve and plan to evacuate and charge with r134a. I understand this is not ideal due to the incompatibility of oils/refrigerants, but as of now he’s not worried about it. He will use it until it stops blowing cold and then just replace the entire system as a whole. I’ll let you know how my experience with that system goes! Haha

I don't recommend charging R-134a into an original R-22 system. The system design, operating dynamics, and pressures are quite a bit different between the two, and so is the oil. If you can't find any R-22, which is being phased out, you could try sourcing DuPont/Chemours Freon(R) MO99 (R-438a), which is reportedly a drop-in replacement for R-22. Both refrigerants are compatible with mineral oil (MO) and alkylene benzine (AB) oil. So unless the system was left open for a long time and/or you need to flush it for some reason, it's just a matter of evacuating and recharging with the correct amount of MO99 without having to worry about the type and amount of oil. Lacking a spec for the amount of refrigerant to charge, you might have to use the superheat and subcooling charging method, though. I would also install piercing valves on both the high and low sides so that you can properly connect your manifold gauge set and vacuum pump.

John, thank you again for the reply.

I have yet to find a R/D that says it's r134a compatible, but will continue looking. It is actually quite difficult replacing this with the grill on the truck, so I may have to remove it again..time will tell!

Try this site's sponsor for an R-134a compatible receiver/dryer. Tim at ackits.com might have just what you need.

Got a text from the neighbor stating that her ac had quit working. I planned on coming home today so conveniently, I was able to take a look. Rented the equipment and checked pressures. It was low on refrigerant as expected, but not low enough to not kick on the compressor. Not sure where the leak is from because I did not have UV die in the refrigerant.

I vacuumed the system down and was able to achieve the targeted 29”Hg or so. Then added some dye to the fill line, and recharged with 24oz of r134a.

When I first stared the vehicle, mechanical fan wooshed, then disengaged about 30 seconds later. I had the squirrel cage fan blowing on the condenser but was still getting some concerningly high high-side numbers. 325psi or so at idle, 82F ambient. Then the mechanical fan engaged a few minutes later and pressures dropped to 35psi and 200psi exactly. Vent temps still only 60F on the dot. It’s cold enough, but I’d like about 40F.

Should I be concerned with the high side numbers before the mechanical fan engages? I’d imagine on a hotter day, without my pusher fan, pressures probably get up to 400+ psi in the sunlight. I don’t want anything to break again..

Lastly, am I still expecting too much from an r12 serpentine style condenser filled with r134a? Perhaps I should switch to an HFC blend or R12 if I can find it. Too late though since I filled with pag46.

I just let the mechanical fan disengage and then turned off my pusher fan and high side pressures are only around 250psi or so. Low side 40psi. Perhaps it just needed time to equalize while filling.

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PromiseRing wrote:Rented the equipment and checked pressures. It was low on refrigerant as expected, but not low enough to not kick on the compressor.

Do you know for sure that it was low on refrigerant? I ask because it's not possible to tell how much is in it by pressures alone. Recovering the charge and weighing it is the only way to gauge the actual amount.
quote="PromiseRing"]vacuumed the system down and was able to achieve the targeted 29”Hg or so. Then added some dye to the fill line, and recharged with 24oz of r134a.[/quote]Vacuum and refrigerant amount look good, but what do you mean about adding dye to the fill line? A half-ounce or so of dye is all that's needed.

PromiseRing wrote:When I first stared the vehicle, mechanical fan wooshed, then disengaged about 30 seconds later. I had the squirrel cage fan blowing on the condenser but was still getting some concerningly high high-side numbers. 325psi or so at idle, 82F ambient. Then the mechanical fan engaged a few minutes later and pressures dropped to 35psi and 200psi exactly. Vent temps still only 60F on the dot. It’s cold enough, but I’d like about 40F.

Elevated high-side pressures usually indicate a condensing problem caused by insufficient airflow. With the engine warm at fast idle, the A/C on, and an ambient in the 80's, I would expect the fan to be roaring most of the time. Even if it's new, the fan clutch could still be out of spec. Something to consider. After the fan re-engaged, the pressures dropped to 35/200, which are just about right for a conversion like this. At those pressures, I would expect to see center vent temps of 45-50 degrees. Does the vent temp drop into this range at speed or does it still hover around 60 degrees? If so, and air from the heater core isn't leaking in, the evaporator might not be sealed enough around its edges, allowing ambient air to infiltrate.