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Chad T's Avatar
 
Join Date: Apr 2001
Location: Columbus OH
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Help With A/C Diagnosis

Hey Guys,

I overcharged my A/C for no good reason and blew out the compressor shaft seal. After researching I decided to try replacing it and see how it worked. Installed the seal and put manifold gauges on. Pulled vacuum for about an hour and the system held vac overnight.

Today I charged the system. I started by charging through the high side with the car off. I put 2 12.5 oz cans of r134 in by heating them up in warm water. So then I start the car and get the compressor running (after I re-adjusted the clutch air gap but that's a whole other story).

Low side was just below 30 and high side was just above 100. Air was blowing fairly cold with vent temps around 50 degrees with a meat thermometer. Ambient temps about 83 (could have been higher as it gets hot in my garage). I decided to ad some more 134 through the low side. After doing this I got the low side up to about 35 but the high side wouldn't go above 150.

The big problem is that when the rpms go up the low side pressure drops instantly and the compressor starts short cycling. It does this at anything much above idle. Got worried about overcharging it again so I stopped adding refrigerant. Good news is the seal seems to be holding so far.

I though I might not have been getting enough air though the condensor but it does the same thing when driving. Cycles on and off constantly. Any ideas? I did ad about 4 oz of oil to the compressor since I lost a bunch out of the old seal. Could this be from too much oil? Compressor bad? Still undercharged somehow?

Any ideas appreciated. I know there are a lot of A/C threads on here and I've read most of them. Don't remember seeing this problem before.

Thanks,

Chad

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1987 951 Sunroof Delete
Old 08-12-2013, 05:19 PM
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Hi Chad,

First, let me suggest a "Signature line" for you:
Car is a 1987 951 with Max951 chips

Nice work on resealing the compressor shaft.

With increased RPM--above idle

LOW SIDE LOW
HIGH SIDE LOW
Short cycles

My guess is a bad expansion valve or weak compressor or over charged with R134a.

You added 4 OZ of oil. PAG or POE and what weight?

If you added 2 cans of R134a to the high side----can you guess how much you added to the low side?

Usually 28 ounces of R134a is all the system needs.

???
J_AZ
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1988 924S, 80K ..+ 1987 924S, 150K DD (+15K est. bad odo)
Old 08-12-2013, 05:59 PM
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Thanks John. Fixed the sig. Been meaning to change it. I didn't have a Porsche when I first joined Pelican. Hate it when I do the double chad.

I put in ester 100 oil since I had no idea what was done when it was converted. It just has a low side R134 adaptor. No A/C sticker under the hood at all. Going on the data that ester is supposed to be more comaptible with the r12 oil than pag. Don't know if that's true or not.

Seems like most of the 3rd can went in. Once the low side started getting close to 40 psi at idle I stopped but I don't know how much I lost purging the hose etc. I also shot a little bit back out when I started thinking it was getting overcharged.

Seems like it's acting undercharged but it shouldn't be. Never checked the pressures before the seal blew but the air worked decent and didn't cycle like that. It was empty for a couple weeks.

Sould I be bumping the revs up to charge the low side? I've found info that says 1200-1500 rpms for charging. Info seems to be all over the place on this topic but it's interesting.

Trying to see what I can get by with on the cheap before diving in with new parts. 134 is getting expensive though. I've got 50 bucks in 3 cans since I didn't see the $9.99 house brand cans at autozone until today.
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Old 08-12-2013, 08:02 PM
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Chad,
POE will mix well with mineral oil, PAG will not. PAG and mineral and PAG with POE will separate. Glad to hear that you added POE.

You mentioned that the system was empty for a couple of weeks. Do you mean it was open to atmosphere? IF so, after you resealed the compressor did you replace the liquid line drier? The drier is a molecular sieve and moisture bolds to the desiccant within. You may have moisture within the system that is freezing at the TXV and blocking flow. This could be the cause of the low suction pressure and compressor cycling.
Old 08-12-2013, 08:48 PM
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The compressor shaft seal was leaking and all of the refrigerant escaped. It was only completely open while I was replaceing the seal which took me about 3 hrs then I vacuumed the system but it was empty for a few weeks.

So moisture could be keeping the refrigerant from returning to the compressor? That makes sense. I assumed a blockage would cause high pressure but I see how it could cause this problem. I did get a big moisture cloud when I first opened the valves to start pulling a vacuum. I did not replace the dryer.
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Old 08-12-2013, 09:19 PM
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I assume the TXV is the expansion valve? If it were freezing wouldn't the high side pressure go up? It was staying steady at about 150 when the low side dropping. Sorry if these are dumb questions I'm new to the A/C diy.
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Old 08-12-2013, 09:36 PM
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On my 84 dodge pickup, the drier came apart, clogged the expansion valve and gave me retarded pressures. I think your expansion valve is either clogged or bad. Change the drier anyways.

When you have 35 on the low side, you should have well over 200 on the high side.

If you pulled a vacuum for a while, you shouldn't have any moisture in the system.
Old 08-12-2013, 10:35 PM
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Chad,

A question; how did you replace the main shaft seal and where did you get the parts?
After extensive work on my AC system over the past few months, it works great but my compressor is leaking oil out of the seal just behind the clutch. Thanks!
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Old 08-13-2013, 03:56 AM
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Quote:
Originally Posted by Chad T View Post
I put in ester 100 oil since I had no idea what was done when it was converted. It just has a low side R134 adaptor. No A/C sticker under the hood at all. Going on the data that ester is supposed to be more comaptible with the r12 oil than pag. Don't know if that's true or not.

True & Very good since the car had been converted and had a low side R134 adaptor

Seems like most of the 3rd can went in. Once the low side started getting close to 40 psi at idle I stopped but I don't know how much I lost purging the hose etc. I also shot a little bit back out when I started thinking it was getting overcharged.

I think you are overcharged. Even with a slight loss of freon while purging the lines

Seems like it's acting undercharged but it shouldn't be. Never checked the pressures before the seal blew but the air worked decent and didn't cycle like that. It was empty for a couple weeks.

Sould I be bumping the revs up to charge the low side? I've found info that says 1200-1500 rpms for charging. Info seems to be all over the place on this topic but it's interesting.

The reason for 1200 rpm or so is to stabilize the idle at a certain RPM rather than just have the computer do it which may not hold constant

Trying to see what I can get by with on the cheap before diving in with new parts. 134 is getting expensive though. I've got 50 bucks in 3 cans since I didn't see the $9.99 house brand cans at autozone until today.

OUCH!
Good advice above from wrench1 & others. Wrench1 posted about the RD- receiver drier. I use cheap Pelican URO brand for about $11 each or whatever is available locally.

You are overcharged.

Before you begin again and without recovery equipment, loose the new (expensive) R 134a...,
Hook up the gauges and purge 2or 3 ounces of R134a, not a lot, watch the pressures and see if it begins to cycle. If nothing happens, repeat. Again, just a couple of ounces of R134a at a time.

Let the system stabilize each time.

If you finally know it is time to open the system and do the repairs as suggested above, and not knowing what was previously done, you may want to do more work.
Remove the compressor and dump the oil-start fresh.
Flush the condenser-backwards from normal flow.
Replace the RD as mentioned.
Do not flush the evaporator.
Remove, flush and inspect the expansion valve for a clog--or just replace.
New "O" rings where ever you can get to.
Replace the AC oil.

The problem you have is the condition of the compressor.

GL
J_AZ
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Old 08-13-2013, 05:36 AM
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Chad- TXV is the thermal expansion valve. Pfarah- seals are available from several online vendors, griffiths is one that will sell to the public. There are two different styles of shaft seals for the 10P15 series compressors, carbon or lip, I prefer lip. PM me for instructions if you like.

The condition which has been described has me scratching my head. 35 and 150 with the ambient 83 or so degrees with vent temps at 50 leads me to believe you might have bad valve plates inside the compressor. Not uncommon with the 10P15E, but you can't find replacement valve plates and rebuild. What throws me off is why it is short cycling. Might be a bad pressure switch, could be undercharged. To test, bypass the pressure switch near the drier and keep a close eye on the gauges. If the low side is not going into a vacuum, and the high side is not sky rocketing, the switch is probably bad.

I don't think you would have lost 4oz. of oil when the shaft seal blew, more like 2oz., the entire system should not have more than 6-7 oz total. Pick your poison, I go with with PAG 46 oil every time I convert, unless it's an R4 compressor. What we do not know is how much of what oil was in the system to begin with. It's a problem when you have too much oil. If you put 4oz directly in the compressor, and did not rotate the clutch, you most likely slugged it and the valves are done. If there is too much oil in the system and the compressor is fine, it will not cool as oil is puddling in the evaporator.

What I would like to know is what the pressure is when at equilibrium.

Just for future reference, never charge on the high side and pay attention to whether you are charging as a liquid or a gas.
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Last edited by mattdavis11; 08-13-2013 at 06:41 AM..
Old 08-13-2013, 06:31 AM
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Hi Matt,

Your information is invaluable.

I am confused about the "could be undercharged" part.

OP added 2 cans and "Seems like most of the 3rd can went in"

On the excess oil, wrench1 said it could end up in the RD receiver drier, I thought some could also just sit in the bottom of the condenser.

If more gets to the evaporator and puddles, how do you get it out? And wouldn't the expansion valve clog?

Thanks
John
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Old 08-13-2013, 07:02 AM
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I'm sorry to hyjak this post but I having read them I am overwhelmed with everyones level of expertise. To continue would it be possible if someone could tell me what the correct pressures should be for R134a at 90 Degrees F and 70% humidity on a 986 2001 Boxster. Im getting loud CHATTER when the clutch is engaged and smooths out at a little higher RPM than 700.
Old 08-13-2013, 08:46 AM
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Quote:
Originally Posted by pfarah View Post
Chad,
A question; how did you replace the main shaft seal and where did you get the parts?
I replaced the shaft seal by removing the clutch and pulley (remove clutch first). Then removed the case bolts and pulled the nose off. Seals are held in with a snap ring. There was one carbon seal, one seal with an o-ring, one case o-ring and some crush washers for the case bolts. $9.95 on ebay. That's all I have in parts so far. Here is the seal I got. Compressor Shaft Seal Kit Nippondenso 10P13 10P15 FJC | eBay Just search for "denso 10p15 shaft seal".

Quote:
Originally Posted by John_AZ View Post
Hook up the gauges and purge 2or 3 ounces of R134a, not a lot, watch the pressures and see if it begins to cycle. If nothing happens, repeat.
I actually did purge some thinking it was overfilled before I drove the car. If I have to dump (have it recovered) the refrigerant I will definitely flush and replace more components.

Quote:
Originally Posted by mattdavis11 View Post
If the low side is not going into a vacuum, and the high side is not sky rocketing, the switch is probably bad.
Thanks for the info Matt! Low side is dropping to around 20 when the rpms rise at all and high side dosen't seem to move when this happens. Everything was working OK before the shaft seal went.


Quote:
Originally Posted by mattdavis11 View Post
I don't think you would have lost 4oz. of oil when the shaft seal blew, more like 2oz., the entire system should not have more than 6-7 oz total. Pick your poison, I go with with PAG 46 oil every time I convert, unless it's an R4 compressor. What we do not know is how much of what oil was in the system to begin with. It's a problem when you have too much oil. If you put 4oz directly in the compressor, and did not rotate the clutch, you most likely slugged it and the valves are done. If there is too much oil in the system and the compressor is fine, it will not cool as oil is puddling in the evaporator.
Not knowing what was in there is what made me want to go with the ester oil. I actually rotated the compressor clutch after I put the oil in and burped the old oil out and some of the new. After it was back on the car I rotated it a few times and rotated it again with the high side under vac to try and pull some of the oil out. I had a feeling it was too much but it was cooling OK at idle.

Quote:
Originally Posted by mattdavis11 View Post
What I would like to know is what the pressure is when at equilibrium.
After I put the 2 cans in the high side (mostly as a liquid but I had to tip the can back up to put it in the hot water) the static pressures were around 88. Started the car and the low side was barely 25 or so and the high was around 100. That's when I went to get another can of 134. After trying to get it topped off the cooling fan was running on high and it was super hot in the garage. Static presures were over 100. Today with much cooler temp (69 degrees) the pressures are below 80.


Quote:
Originally Posted by mattdavis11 View Post
Just for future reference, never charge on the high side and pay attention to whether you are charging as a liquid or a gas.
Not even under vac with the car off as a precharge? My original intention was to just precharge with one can but I had read about heating the cans to get the full charge in there so tried that and was able to empty 2 cans that way.

Would it be worth trying to raise my rpms and top it off until the low side pressure quits dropping?
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Last edited by Chad T; 08-13-2013 at 09:05 AM..
Old 08-13-2013, 09:00 AM
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Quick update. Just went out and fired up the car since I had the hoses attached. Now at idle with the compressor running I'm getting about 25 low and over 200 high with 73 degree ambient temp. When I rev the motor low drops to 20 and the high side shoots up to 250+ quickly. Vent temp today is 40 degrees and the compressor is not cycling.

Is it possible I froze the eveporator yesterday? It was hot and humid. The high side didn't rise with RPMs like it's doing today. Put the rest of the extra can of 134 I had in there and after running for a bit it was at about 30 on the low and 225 high at idle. Ambient temp rises quickly in the garage with the car running too.

Would a frozen evaporator cause the low side pressure to drop below the cutout with increased rpms?

Still confused about what was going on yesterday but tempted to just roll with it with the 40 degree vent temps today.
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Old 08-13-2013, 11:07 AM
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Quote:
Originally Posted by mitchellb View Post
I'm sorry to hyjak this post but I having read them I am overwhelmed with everyones level of expertise.

To continue would it be possible if someone could tell me what the correct pressures should be for R134a at 90 Degrees F and 70% humidity on a 986 2001 Boxster.

Im getting loud CHATTER when the clutch is engaged and smooths out at a little higher RPM than 700.
Let me try.

"Normal" R134a LOW pressure is about 27-30psi.
"Normal" R134a High pressure is "ambient temperature" ---the temperature in front of your radiator grill multiplied by 2.2.
So...90*F X2.2 equals about 200psi on the high side.

Humidity of 70%---HERE is the CHART--Pressures increase.
RELATIVE HUMIDITY

Now for the CHATTER.
Has your 2001 Boxter had the Intermediate Shaft Bearing replaced?

Did you know this is a flaw in the Boxter engines until 2007?
Did you also know that the founder of Pelican has written many books and tech articles about the flaw?

Here to begin:
Pelican Technical Article: Boxster Intermediate Shaft Bearing Replacement and Upgrade (IMS) - 986 Boxster (1997-04) - 987 Boxster (2005-06)

The 2 problems may not be connected.

GL & welcome,
J_AZ
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Old 08-13-2013, 12:08 PM
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Too much oil, compressor is fine. Remove some of the oil through the high side with the car on, compressor engaged. Have a rag handy to cover the yellow charge hose so as not to lose the o ring or become an oily mechanic.

Two or three second short bursts at operating temperature should purge enough oil to bring the high down. Sub 20's on the low and above 200 means the compressor is doing it's job. You may have to add more refrigerant after the oil is purged.

John_AZ, oil tends to puddle in low pressure locations, which would be in the evaporator. The short cycling the OP had was most confusing considering the information provided. I'm still at a loss to describe how it could have occurred given the charge quantity. Systems will settle down after awhile. Maybe the OP's gauges are not of quality to accurately diagnose what is going on no matter how well versed in a/c one may be.

I'd let some loose from the high to purge oil.
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Old 08-13-2013, 04:11 PM
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I just re read what you have, leave the system alone. It will settle down.
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Last edited by mattdavis11; 08-13-2013 at 04:34 PM..
Old 08-13-2013, 04:25 PM
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I did notice when I disconnected the high side hose there was lots of oil coming out. Maybe shoot a bit more out? Or just let it go since it seems to be working? Won't be hot enough here for a while to give it much of a test. It's weird that the high side is acting so much differently today.
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Old 08-13-2013, 04:34 PM
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Ignore my last post. Open the high with the compressor engaged and engine on. Add more freon to satisfy the system if need be, but do not add more oil.
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Old 08-13-2013, 04:42 PM
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Great. Thanks for your help Matt!

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Old 08-13-2013, 04:53 PM
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