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Cannot get car to take full refrigerant charge

James89dx on Sun March 29, 2015 2:19 PM User is offline

Year: 1989
Make: Honda
Model: Civic
Engine Size: 1.5
Refrigerant Type: R12

1989 Civic R12 A/C system

Four Seasons rebuilt compressor failed on me last year. Replaced the entire system this January (again, for about the 3rd time in 5-6 years due to these horrendously crappy Sanden TR70's). Compressor was a (supposedly) brand new OEM Sanden from I added 1/4 of dye as I have been doing on all my new systems for some time now so I can periodically check for leaks.

That compressor started leaking on me at the pulley area after not even a month. has no more "OEM" Sandens and best they could do was send me an aftermarket clone and refund me the price difference, so I went that route.

Last night I replaced the compressor (drained oil from old compressor, replaced that same amount of oil to new compressor - added a little bit due to oil loss when removing the lines etc).

Anyway, so I'm trying to charge the system now. The OEM service manual calls for 30-34 oz of R12. I've currently got 26.5 oz of R12 in it and the car will NOT take any more refrigerant. At first I thought my 30 lb R12 cylinder was empty, but I closed the valves and held the tank and I can definitely feel a dense refrigerant presence in the tank. I know my 30 lb cylinder is close to empty, but after my last charge I calculated I should have right at 30 oz in the tank. So at best I do only have a few ounces of refrigerant in the tank. I even put the cylinder in a big tub of hot water to try to help it (which is what I had to do in January when it was cold outside), but that didn't work.

Here's my predicament - I would like to get at least 4-5 more ounces of R12 into the car. I do have a bunch of R12 cans, should I try getting a few more ounces of refrigerant into the system via a can? Would the can be prone to the same issue as the 30lb cylinder?

OR perhaps if I wound up with a little bit more oil than I anticipated (perhaps 1 oz "over" at best). Would that prevent the system from taking any more refrigerant?

The car IS cooling and the temp at the vents feel fine. However it's only about 80 here in Dallas today and I want to make sure this car cools when it starts getting up into the 90's.


mk378 on Mon March 30, 2015 11:29 PM User is offline

What is the static pressure in the cylinder? If it's less than the saturation pressure (Look up the ambient temperature on the temperature scale on the gauge), there is no liquid there.

There should be a sight glass. R-12 TXV cars can be charged by observing the sight glass.

If you were to severely over charge, other things will become apparent-- like no cooling, tripping the HPCO, or blowing the high side hose, well before it stops taking refrigerant out of the tank.

Edited: Mon March 30, 2015 at 11:32 PM by mk378

James89dx on Tue March 31, 2015 9:20 AM User is offline

I do have a sight glass on the drier and have always read about charging by sight glass but I have never been skilled enough to differentiate. IIRC it's something like when the sight glass has no bubbles it's done?

Turns out this is kind of moot because a day after charging the system I discovered a leak at the compressor/suction hose junction. So I took it all back apart last night after work and went with a slightly "fatter" o-ring there. Vacuumed it all down again and let it sit overnight. Check it this morning and it lost 3" of vacuum in 12 hours. I know many OEM's only call for letting it hold vacuum for an hour or two but I always like to let it sit at least overnight. Not sure what to make of the 3" vacuum lost, but I will check it again after work to see if it's dropped more.

For my own personal knowledge/future reference, help me understand the bit about the saturation pressure. I did some Google searching and came across this table:

If I'm understanding this correctly - for example let's say it's 80 degrees F ambient temp. The chart is in Celsius so I find 26 C on the chart. That shows a kPA of 668.5 for 26 degrees Celsius. I checked the conversion of 668.5 kPA to PSI and it shows to be right under 97 PSI. Does this mean that if it's 80 degrees ambient temp and my R12 cylinder has a static pressure of less than 97 PSI that basically all the R12 is gone? Or am I doing that wrong. Thanks! This is good info for a n00b like me

wptski on Tue March 31, 2015 10:13 AM User is offline

This chart shows at 80F as 84psi so anything less means no liquid refrigerant in the system.

I have a recovery machine which I left under a vacuum last summer and it still shows it holding the vacuum. I've seen a system hold a vacuum but not pressure. I have a vehicle that held a vacuum, held 150psi of nitrogen for a week yet has a small puddle of oil from the compressor after some sub zero temperature.

Edited: Tue March 31, 2015 at 10:15 AM by wptski

James89dx on Tue March 31, 2015 11:01 AM User is offline

Hmm I wonder why the discrepancy on the chart(s)? I found this other chart here

it shows the saturation pressure of R12 as being 98 psi at 80 degrees which is very close to the 97 PSI I came up with from the first link. Also - does no "liquid" refrigerant mean the same as just plain layman's terms of "no refrigerant"? I've only ever charged my cars as a gas and never messed with the upside down liquid stuff.

Yes I've had this same car on previous jobs hold vacuum for a week. So something is definitely up. I'm really tired of messing with this car though. I swear I must be on AC job number 6 or 7 on this car in about 8 or 9 years all in the continued quest for a reliable AND cold A/C system. I wish Honda hadn't cursed these with the TR70 compressors.

HECAT on Tue March 31, 2015 12:47 PM User is offline

The liquid vaporizes as it is charged in as a gas. This vaporization is measured as liquid weight loss, as we charge by weight.


HECAT: You support the Forum when you consider for your a/c parts.


James89dx on Tue March 31, 2015 1:34 PM User is offline

So at 80 degrees is the saturation pressure 98 PSI or is it 84 PSI?

I know there is refrigerant left in it because I can feel it and also if I crack the valve there's a nice healthy PSFFFFFFFFFTTTTTTTTTTTTTT

mk378 on Tue March 31, 2015 7:13 PM User is offline

It's a good practice to static test a R-12 system under pressure with some other gas before committing to charge the R-12. Some leaks might hold vacuum but leak under pressure.

You are seeing two numbers because 98 psi absolute is 84 psi gauge-- which is what you will measure with an ordinary gauge at sea level. So the number you need is 84. The absolute pressure is of interest to physicists and engineers and those who have very expensive absolute pressure gauges, which are typically used only in laboratories. Although the new digital manifolds are probably measuring absolute then subtracting 14.7 to show to the user.

Edited: Tue March 31, 2015 at 7:16 PM by mk378

James89dx on Wed April 01, 2015 10:15 AM User is offline

Ahhhhh. Now I get it. Thank you

So last night after work I checked the system again and it had lost 9" of vacuum in 24 hours. Since I had already put some dye in to the system previously I leak checked all of the junction points in the system with my UV light and couldn't find any. I pulled the evaporator out hoping to find evidence of leaks maybe on one of the expansion valve junctions but found no trace whatsoever. I was hoping that would be the culprit so I was disappointed it wasn't, because this meant I had a seemingly untraceable leak. So I reluctantly put it all back together and vacuumed it down again last night.

I checked this morning and it lost about 1/2" of vacuum in 12 hours. Much better but still some loss. I'll be curious what the loss is tonight after another 24 hours. I'm almost hoping it's leaking between one of the service fittings and my manifold gauge set. I noticed the little rubber ends of the hoses on my manifold gauge set are getting pretty deformed. Is there a way to replace those? I looked online but can't find anything about it.

wptski on Wed April 01, 2015 7:12 PM User is offline

Depends what brand of hoses you are using but they "may" be same for most brands like these.

James89dx on Wed April 01, 2015 9:34 PM User is offline

Thanks, I'll try to find out if those fit. I have a CPS brand manifold set

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