AC recharge R-12 cab air conditioner question

[AtlantaCamper]

I'm thinking of giving my cab AC system a charge with R-12 to improve the cooling ability of the cab AC.  The system is working and I don't think there is a real 'leak' to speak of, but I suspect that over time some of the R-12 has been lost past the seals.  The AC compressor and clutch function and I do get cool air.  Cool, not cold.  At a temperature of ~87F ambient and ~50% RH the temperature at the vent is about 57F.  Should be ~40F to 45F.  If it works, it would be a noticeable improvement and I rely on the cab AC while driving to keep the folks in the back a little happier.  

I have all of the things I need to do this:  manifold gauge set, an unopened 12 oz can of actual R-12 refrigerant, can tap and connectors and thermometer.  It's something that has to be DIY I believe because no shop will do this anymore with R-12.  While I have not done this process myself before I have read up on the process and I'm willing to give it a try.  A mechanic friend who loaned me the manifold is willing to help too.  Worst case is that I screw it up and I have to switch everything over to R-134a.  It seems so much easier to just give it a goose with a charge and let it stay as R-12 for now.  As long as I don't over charge it I should be ok and I suspect that the charge would last a few years.  Anyone have comments or can anyone correct my assumptions if they are totally off base?

This is my compressor rear end.  Note that the low side connector access is blocked by the support piece that connects between the engine and the under side of the intake manifold.  I suppose I'll have to remove that to do this job.  It's all pretty tight in this area due to the extra house battery being located in the engine compartment:

(if the resolution is good enough on the upload, the keen observer will notice a spider in the bottom right corner of the picture - probably blinded the little guy when I took the photo...)

Before resorting to a charge, I did go through the rest of the system to make sure there were no obvious issues.  I got access to the evaporator coils by removing the fan behind the glove box (the fan had some seeds and tree bits in there that rattled around on max fan speed so I needed to get in there anyway).  With the fan out you can stick a cell phone up there and take a picture.  This is before I cleaned the coils:

I had 2 cans of coil cleaner that I was going to use to clean the house HVAC coils.  Turns out that after doing this residential job there was just enough left over to clean out these coils.  Before you do this make sure that the drain tube for these coils is clear - mine was partially blocked and I had to blow backwards to get it really cleared out.  You can't see what you are doing but there is just enough room to get the can up there so you can spray the foam, again using the cell phone camera to check:

The coils after rinsing with a hose (all water drained out and then I left it alone to dry for 3 days before retesting it):

My coils were not all that dirty, but I did get a noticeable increase in overall air flow after this procedure.  Next time you are in there cleaning out your cage fan you should check your coils!

Speaking of this darn cage fan behind the glove box - that thing is always getting some gunk in it and making terrible noises.  There isn't any filter on the cab air intake as far as i can tell.  I think the air comes from either the vent outside near the wiper arm connectors (lever on 'fresh') or from under the dash (lever on 'recirculate').  I think the junk comes mostly from the 'fresh' setting when stuff drops in after getting in from the outside vent inlet.  Is there anyplace to put a make-shift filter on the 'fresh' intake side?  I'm thinking of just using the 'recirculate' setting and then putting a simple screen filter over the inside intake that looks like this:

Should be pretty simple to tape a square of filter over this inlet.  something that is open enough to not hinder airflow but a tight enough screen to keep the larger stuff from getting in the fan.

Thanks to any who might be able to inform me about this R-12 charging task before I go off and try it.

[Odyssey 4x4]

It sounds like you know what you're doing and are going about doing it the right way. I will say this though, I am rebuilding my 1990 and the air was the same as yours, cool but not cold. I pulled the AC system apart and replaced my condenser coil and will be doing the evap coil soon as well as the compressor. Multiple of the o-rings were wasted, they took on the classic crushed triangular shape rather than the flexible round shape they required. Unfortunately, I forgot to take a picture. Yours being even older than mine likely has the same issues going on which is normal for the age of these vehicles. When you attempt to charge the system, keep the gauges on it for a while and confirm that its holding a steady pressure, even after 30-45 minutes of sitting. If it has a leak obviously you're going to lose the precious R12, but you'll know the issue in the system. 

Also, considering the system is still R12, it's likely still the original compressor. The compressor is likely nearing the end of its life and not able to perform the way it did when new. Valves wear, bearings, etc.

 

 

[AtlantaCamper]

Very good insights Odyssey 4x4, thanks!    I'll watch the pressures carefully.  I can imagine that a system with poor seals on the o-rings might hold just enough pressure on the low side to work a little but then the additional pressure from the charge might just sneak past those o-rings pretty quickly and come right back to the cool-but-not-cold performance level.  

45 minutes ago, Odyssey 4x4 said:

considering the system is still R12, it's likely still the original compressor

This is quite likely the case.  If my experiment fails then I'll go the full replacement route, but I'm not going to have the time for that any time soon. It's a $33 investment for the R12 and doesn't take a lot of time.  I've got a backup plan to find the remaining R-12 a good home too.  Regardless of success or failure on my rig there will likely be R-12 left over and I've got two old cars in the neighborhood that could use a charge and I'll make the rounds once the can is open.  Once that can is cracked I can't imagine it would be willing to stay in that can for any length of storage.  

 

[jjrbus]

I suspect more damage is done by giving it a shot of gas than any other cause!   Check the pressures if they are right do not add any refrigerant! 

I switched my system over to 134A,   If I had just added gas I would never have found this and no matter what I did it would never have functioned right.  It is not a nest just a long term accumulation.  The evaporator was so clogged that it was easier to replace than clean!

Can too much Freon damage compressor?

A: It is possible to overfill an air conditioner with refrigerant and, unfortunately, several problems can occur that could permanently damage the unit. ... Overcharging the unit can cause permanent failure of the compressor, which is the pump for the refrigerant.

 

 

 

[Odyssey 4x4]

yup, fortunately he was able to clean the evap coil which should give accurate hi/low pressures on the manifold. If the evap was still plugged up his readings would be all kinds of screwed up. Unfortunately, he cannot disassemble the system without losing his r12 charge unless he has a recovery tank.  After that he might as well convert over to 134. 

[AtlantaCamper]

1 hour ago, jjrbus said:

Check the pressures if they are right do not add any refrigerant! 

Yes, this is absolutely the right approach.  If it is anywhere close to correct working pressures (still have to find those specs... :0) then I'll leave it alone and not do anything.  I'd rather have a working system that is "cool" than a blown compressor (_not_ 'cool').  I should be OK if I just go slow and watch the pressures.

I don't have a recovery tank so if the re-charge approach doesn't work I'll be doing a full swap over to 134a.

[jjrbus]

When I looked my system over,  there was not refrigerant in the system,  the compressor was covered in oil, the hoses were over 20 years old.  Not knowing the condition of the compressor necessitated replacing the coil and dryer.  So I just replaced everything and converted to 134A.   It is nothing to brag about but it works.  If the charge is not spot on, the evaporator will freeze up.. 

[Donnie]

Coming in late on this.  I'm not sure if Toyota used a sight glass in their system back in the R12 daze, but if there is one, it can be a view into your line to see if there is adequate  coolant...........   Any  leak in the system will show itself  by the oel  at the  faulty 0 ring, fitting, compressor seal, etc.  .... there is no sump in the compressor. The oel is suspended in the gas & travels thru the system...   There is  a safety plug somewhere in the system that will pop at extremely high pressure & allow the gas to escape...This can happen if there is blockage in front of the condenser, a faulty fan clutch, or overcharging  the system....German vehicles located the safety plug low in the system, usually in the dryer so the escaping gas would exit below the engine......... I am not sure how much of this info applies to your vehicle........theory, yes.....sight glass not sure.......donnie

[AtlantaCamper]

3 minutes ago, Donnie said:

not sure if Toyota used a sight glass in their system back in the R12 daze

I have not seen a sight glass so far.  I believe most of these systems, including mine, are aftermarket AC systems, not OEM.  The label is gone on my compressor so I can't read anything to get a model number.  

I'm trying to determine what the "proper" pressure readings should be but I have not found any reliable data so far.  Anyone know if there is a 'standard' aftermarket compressor type and spec for these rigs (mine is '87)?

Pretty generic data I'm seeing on R12 systems is between 25 and 40 psi on the low side, and high pressure reading of 200 to 225 psi.  I haven't been able to get the time to measure my system yet.

[WME]

http://rechargeac.com/how-to/ac-system-pressure-chart

This is a temp vs pressure for a correctly operating system

[AtlantaCamper]

1 hour ago, WME said:

temp vs pressure

Good to know that pressures are basically the same for a properly operating system with a particular refrigerant.  I wasn't sure if this was the case or if there were specs specific for a particular compressor. That chart is for R134a.  Although the pressures seem to be relatively close, R12 is correspondingly a little higher. For example if R134a should be 36 psi, R-12 would be 43.  I found a handy chart comparing R-12 and R134a, plus it adds an extra level of detail by specifying the relative humidity and giving the temperatures of the discharge line out of the compressor:

The link you sent had a super handy summary of how to interpret the pressures.  The only time you add refrigerant is if both readings are low, which seems fairly obvious although its nice to see it in writing.  Otherwise it is fairly intuitive in terms of the what and why when you have one side higher than normal and the other side lower.

[AtlantaCamper]

I finally got around to doing the AC charge with the can of R12 I received.    Although the system was low on charge (both low and high were below spec pressures), the addition of refrigerant did not have a huge impact on the system performance overall.  Vent temps dropped 4 degrees F, but were still higher than the expected vent temp range of ~40F to 45F by a good bit.

Initial readings at 45 %RH and 85F:

• low: 15 psi 
• high: 195 psi 
• vent temp: 57F

Post charge readings at 45% RH and 90F:

• low: 25 psi constant
• high: 240 psi (variable with peaks up to 275 psi)
• vent temp: 53F
• hose to the evaporator was 60F (R-12 discharge temp) and out of coils was ~130F, which seems normal

Overall the data and system behavior suggests that the inability of the low side to get above 25 psi indicates a blockage, problem or obstruction in the expansion valve.  The intermittent high readings on the high side with constant low on the low side support this I think. The system appears to be limited by the bottleneck in the expansion valve and this limits the overall vent temps in the system as it is.  I may take a little charge out of it now since the expansion valve problem could hurt the compressor at full charge due to the pressure spikes as it cycles on/off.  Hopefully this data/thread can help someone in the future diagnose their ac issues.  (I even bypassed the heater core to make sure no extra heat was being added to the air flow path.  No difference.)

I can live with the existing AC performance for the time being but if I want any improvement or there is any problem I'm going to have to go the full conversion route to R134a from R12.  This is a pretty big task and I'm not ready to do that just yet.  Still, with this experience I'm now confident that I could do that task when the time comes.  It's too bad that changing the expansion valve requires removing the refrigerant and then taking the whole evaporator assembly out from under the dash.  Then you have to change the accumulator out and swap every o-ring and then vacuum it down and leak test, etc.  Probably makes sense to swap the compressor at that point... That's a lot for 10 degrees more of cooling.... I think I'll stick with what I have for now.

I just got back from a week in the Great Smoky Mountains National Park.  Turns out I only needed my AC for the two hours going out of and then returning to Atlanta!  The rest of the time it was so cool and pleasant in the hill country that I didn't use it.   The national park campgrounds there are really nice and we like the fact that almost all of them had no electric or other hook ups.  No issue for us and it kept everything quiet  there.  Temperatures were so mild that we didn't need anything more than a bit of fan cooling during the day.  We camped right next to rivers or streams every night, sometimes with no neighbors for a hundred yards.  Now, getting up and down the hills to get to these sites is a different story, one that I'll post as an update to this topic: 

 

[jjrbus]

Were the doors and windows open when doing,  was the cabin closed off from the cab when checking?  Makes a big difference in mine as the system is not large enough to cool the RV part. 

 

[AtlantaCamper]

47 minutes ago, jjrbus said:

doors and windows open

Yes all doors/windows open, with fan on max and letting pressures stabilize at 2000 rpm

[jjrbus]

14 hours ago, AtlantaCamper said:

Yes all doors/windows open, with fan on max and letting pressures stabilize at 2000 rpm

I had to close doors and windows and close off cab to get system to operate properly. Many report that in order to get adequate cooling they must block off cabin.

[Oldgriz]

A couple of rules of thumb in diagnosing a/c problems. Air flow - are the evaporator and condenser coils clean and free of obstruction ? Are the fans clean ? Are they pushing enough air through the coils ( fan speed RPMS ? )

look for 20  to 25 degree temperature drop across the coil , return temperature - supply temp = TD

 If you don't know the system charge ,Most systems are designed for a 120 degree condenser temperature using a pressure / temperature chart convert refrigerant pressure to temperature , charge system till you hit condensing temp R134 A 120 degree condenser temperature = 185.25 psig .   ( @ sea level ) R 12 120 degree condenser temperature = 170.99 psig (@ sea level ) 

Over time the TXV power heads can lose the sensing bulb charge , the metering pins can stick ( especially in R134 A systems ) you can test the power head by putting the TXV sensing bulb in a cup of hot water and if it starts to work ( when it hasn't been working ) then it needs replacement.

Formula 409 work's great as a leak detector , the smallest leak will bubble up.