Andrew B.

Hello everyone,

I'm currently burning in my car at 80+ weather here in Seattle. I know a mechanic who has equipment for testing/filling 134A and we tried refilling my AC today.

Here's the scoop. We disposed of the old gas and tried injection the new gas (both 134a of course). And when we were pumping the new gas (while the car was running), it only takes 7oz and it stops taking any more.

What should I do?

Andrew
'84 928S

Greg86andahalf

Andrew,


so many questions to ask-

Did you vacuum the system down, not just evacuate, but pull a vacuum?

Are you positive that you are charging through the low side fitting?

When charging, is the compressor turning? It must be engaged for the system to take the freon. If it is not engaged, jump the low-pressure cutoff switch wires to get the compressor engaged. After about one 12oz can, it should run with the switch wires hooked back up.

Are you charging with a manifold and gauges?

Not directly related to the 7oz problem, but important to ask-

When the car was converted to R134, what else did you do to the system and what parts were replaced?

What oil was used in the retrofit?

R134 is charged only to about 80% the capacity of R12. I would not put more than 28oz in and then check vent temps and high and low gauge readings. It is possible to "charge through" the optimum capacity and overcharge which will not yeild the best vent temps. 28oz, check vents, add a splash more while checking vent temps and pressures.

Let me know some of the answers to the questions, I'll try and help.

Greg

Andrew B.

Greg
Thanks for replying

We use vaccum pump to remove the old out.
is the Low side near the front bumper with a little window to see the freon?, thats is where i tried to fill it.

I am charging with low and high gauges, low side shows about 90 then stuck there(engine is running), no bubles running in after about 7oz

The problem i have is i am not sure if my A/C has been converted to R134 or still at R12, how can i tell?

thanks
andrw

Greg86andahalf

Andrew,

This is long, but I'm trying to cover all the bases for you. I hope someone else jumps in to help.

[quote] is the Low side near the front bumper with a little window to see the freon?, thats is where i tried to fill it. <hr></blockquote>

Your 84 may be different than my 86, but if you are referring to the service port on the drier, Thats the High side. Do not charge there. The low side on my 86 is basicly on a line under the upper radiator hose it is hard to see and get to. You only charge only through the low side.


[quote]I am charging with low and high gauges,<hr></blockquote>

where were you attaching the high side hose from the gauges? Do not open the high side on the manifold when charging. Your freon can may explode.


[quote]i am not sure if my A/C has been converted to R134 or still at R12, how can i tell? <hr></blockquote>

Well, that can be tough the determine. If R134 was added, the service port fittings should have been changed to the quick release type R134 adapters. These fittings screw onto the existing R12 service fittings. Also (although few people do this) there should be a sticker indicating the change to R134 and the date it was done.

I'm wondering, were the adapters were already there when you started?

Also, the high side R134 fititng is different from the low side to help people not make the mistake of charging through the wrong (high) side. BUT, that's assuming that they were installed on the right service ports to begin with (most R12 high and low fittings are the same size).

Dozman is trained to recover and identify freon types. Maybe he can chime in and tell you what else to look for in terms of identifying what's in there.

The bad thing is that we know that some R134 is in there (7oz.) Did you add any oil and if so, what type was it exactly? This may determine where to go from here.

Possibility 1) there has been a previous R134 conversion done, complete with flush, O-ring change, new drier, poss. new expansion valve and existing oil removed and new ester oil in the proper amount added. If this is the case, all you are doing is trying to recharge the system. You should vacuum the system down (vacuum through both high and low sides, open both sides of the manifold, you will see both high and low gauges go negative) to at least 29hg for about an hour. Shut both sides down on the manifold. Remove the vacuum pump. Let the system sit and see if it holds the vacuum. If it doesn't, you have to find the leak before proceding. If it maintains the vacuum, your'e ready to charge the system. Charge into the vacuum on the low side. That means that you have the manifold set up so that you can attach the freon can to the charge hose, and when you open (SLOWLY) the low side ****, the vacuum will pull the freon from the can into the system. The rest of the charging will be done by running the compressor and charging the system on the low side. Refer to my provious post about over-charging.

Possibility 2) The system is R12 and you added the adapters and some R134 to a R12 system. If that's the case, did you add any oil? if so, what kind exactly, if not, I will have to check on what would be the best way to go. A new drier will be needed either way, but my gut feeling is to evacuate the 7oz. of R134, replace the drier and vacuum the system down for a few hours. Add two oz. of mineral oil, then charge into the vacuum with R12. Some people (including me) use ester oil in R12 systems(ester is compatible with R12 and R134). But NEVER PAG (R134 oil) in R12 systems. Someone may want to add their opinion on what to do with a R12 system which has had some R134 added to it.

Alot to digest, I know, but all relevent to getting your system back to good operating condition.

Greg

Andrew B.

Greg,

The port i am guessing to be a low side has a cylindrical can(looks like a small oil filter) with a glass windows on top, i can see liquid in it (before). Is this the high side? I think this is the high side.

I do have a quick release fitting in it already. OHoh, I am charging in the wrong port.

I do have a quick release in the high side, vaccumed the port today and will fill in tomorrow.

thanks again

Anrdew 84 928

Greg86andahalf

Andrew,

Yes, that is the high side. You must find the low side port and put an adapter on it. Do you have a charging manifold, or a single gauge?

If you have a manifold with high and low side gauges, monitor the high and low side while charging through the low side only. Engine at about 1500+ RPM (a screwdrver handle positioned between the lower radiator hose and the throttle cable plate will hold the RPMs for you. A/C on max cool, fan on high, windows down, sunroof open.

If you have a single gauge, monitor the high side while charging through the low side.

Release the freon into the system SLOWLY. After two cans are in, monitor the vent temp while slowly adding more freon. If you add too much freon, (anything over 29oz R134 seems like too much to me) you may see the vent temp start to rise as you have charged through the best amount to have in the system. You can always purge a little freon out if you over-charge, but too little R134 is better than too much.watch the high side guage. anything over 225, stop charging.
Your vent temp should be good. If not, we have more work to do, don't keep adding freon.

If you get that far, please let me know. I would also like you to post the high and low pressures and vent temp. at 1500 RPM. and the outside air temp while you were doing the work.

Good Luck,
Greg

iantdopps

To get to the service port, take off the plastic intake tube on the passengers side. Look down and you will see a silver/metal line under there, with the low pressure valve on it, in the area under the support bar that goes across the engine. Some people may not like it, but I have used the 134a kits that come with 3 big cans with the coolant, oil, and leak sealer all in one can. I have done it on 5 cars, and it works great. Hope that helps!

Mike Schmidt

[quote]Originally posted by Greg86andahalf:
<strong>watch the high side guage. anything over 225, stop charging.</strong><hr></blockquote>

What are the ideal high side and low side pressures for R12 and for R134? Do the ideal pressures vary much with the ambient air temperature?

Greg86andahalf

Hi Mike

"Ideal Pressures" are usually given as a pressure range at best. Temperature (both ambient and system temp) has everything to do with pressure.

Here is info given to me by a well-respected 928 A/C authority.

"Pressure charts and books. You can read all the books you want and look at all the charts, some will say the same and some will be out of this world. The PT charts are a good guide line but based on what I have seen over the years you have to look at the entire system"

The R12 gurus tell me they look for high side pressures about 2.2 times outside air temp (OAT). OAT is measured 2" in front of condenser. Also, this pressure target is based on a system in good condition with sufficient airflow through the condenser (sometimes a box fan blowing at
the condenser to replicate car in motion ram-air), engine on fast-idle.

The 2.2 figure in reality ends up being a bit low when testing in the garage. I was targeting 250 with OAT of 85deg. on my R12 928, I charged by weight and was at 275. I could sprinkle some water at the condenser and let the fans pull it through and the pressure would drop to 260 because the condenser (and freon) temperature was being lowered. I made some inquiry’s and the general opinion was that the car at 50mph would allow enough cooling to get the pressure down to the 240 range. Airflow is key to keeping the high side at a reasonable level. IF you have the proper amount of charge and the high side temp is high, check the airflow through the condenser.

IMO,
R-12 high side ideal pressure? 180-250

Low side pressure relates directly to what temp. you can expect at the vent.

My R12 chart in the book shows expansion valve type system (928 is such) pressures:

PSI______evap temp
10 ----------2
12-----------6
14----------10
16----------14
18----------18
From this point on, the PSI number is almost exactly the temp number within a degree or two.

Here is more info given to me by a well-respected 928 A/C authority.

"Frankly I ignore the low side unless I have a problem on the high or with vent temps."

I understand what he is saying. If the high side is under control, and the system works properly, vent temp should be good and the low side pressure should be good as well. If there is good high side pressure and the vent temp is high, the low side pressure can be a diagnostic tool.

IMO-
R-12 low side ideal pressure? 30-45


R134 pressures- Here, the chart changes bigtime.

For high side R134 at 80-90 deg OAT, the chart shows 140-235!!! (quite a range). Bear in mind, on a R134 retrofit system, you get these readings with only 80-90% R134. The amount of R134 charged into a retrofit is supposed to be 80-90% by weight of the called for R12 capacity. It appears that you can yield about the same high side pressures, but are using less R134 to get there. Overcharging is the death nail of a retrofit system. In fact, when you are at full R134 charge, there should still be some bubbles in the sight glass.

IMO
R-134 high side ideal pressure? 180-215

R134 Low side pressures-

PSI_________evap temp
16-29---------33-50
19-39---------33-60
25-43---------40-65
37-51---------48-65

So it appears that the low side pressures, when correct, will be lower on the R134 system than on the R12 system.

IMO
R-134 low side ideal pressure? 26-34

****Disclaimer***

All of the above information and has been gathered during my recent major A/C overhaul I performed on my 86.5 928 and my 83 Suburban R134 retrofit. I spoke to many knowledgeable people on this board, the Rennlist email list and other sites like aircondition.com. I have relied on the Mastercool Basic A/C training manual.

I welcome anyone’s input and disagreement on what I have stated. We learn by discussing technical issues, I am in no way an “expert” on this subject, I just ask allot of questions and try to remember the answers.

HTH
Greg

Dozman

About the only way to tell what refrigerant is in your system with out an analyzier:

When the engine compartment is at ambient outside temperature. Connect your guage set to the high and low side ports, check for differential pressures if any (system should be equalized). Then look at a PT Chart and look up what refrigerant best suits the temp/pressure relationship of your readings. Post your P/T readings.

But, Beware! You don't know what might be in the system. There could be a mixture of refrigerants, or could be one refrigerant with non-condensables.

If one does not know what is in a system, the best thing is to recover the system, and proceed with caution. If you want to put in R134a, make sure you put in the retro kit. You would hate to blow your charge out, due to a leak. What no a/c... What I might damage the compressor... What I need to spend more money...How much oil to add due to a leak... You will be asking many more questions later.

It's best to error to safety, than to proceed with guessing.

<img src="graemlins/a_smil17.gif" border="0" alt="[blabla]" />

John D.
'85 928 Black, Auto

Greg86andahalf

Hey Dozman,

Glad to see your response! Seems like a while since I've seen you here.

Greg

Dozman

Thanks for noticing. I am almost caught up on all the posts. I have been working 12-16 hour days for weeks on end.



John D.
'85 928 Auto, Black

Greg86andahalf

$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$$

Mike Schmidt

Thanks Greg. That's exactly the kind of information I was looking for.

Andrew B.

COLD A/C!!! COLD A/C!!! YES!!!

Thanks Greg, all the info helped. We were able to charge the system through the low side, the adapter for the high side didn't fit though. We had to change the adapters.

Ahh...nice and cool.

Thanks again.

Andrew
'84 928S