Very high discharge pressure after A/C rebuild

[94blue]

High gang. I need to get some input on a 134A A/C problem. My compressor developed a shaft seal leak so I decided to rebuild the system. I just installed a new FS10 compressor, acumulator and oem (blue) orifice tube in my 94 2.3L ranger. I vacumed the system down to -29 psi for and hour, let it sit for another 1/2 hour without leakage, then put two 12 oz cans of 134a in it. I'm gettin good readings on the low side, 32 to 40 but the discharge is reading a whopping 375 psi! I saw it hit 400 psi when running the engine at high RPM. Ambient was 100 degrees. I closed the cab up to cool down the interior and saw a low of 53 degrees at the center vent.
Oil (PAG 46)...3oz removed from old and replaced in new compressor, removed 3/4 oz from acumulator, put 2 3/4 oz in new acumulator.
Vacumed through both high and low port. When i disconnected the high port hose there seemed to be a lot of oil spill. Oil plugged up condensor maybe? i have maybe 15 minutes run time on it. Maybe some oil needs a chance to get moved around?
Thanks in advance...

 

[doorgunner]

they told me to run some water over the condenser to see if the pressure dropped to normal.....if it did--the condenser wasn't getting enuff cool air

they also said that some compressors need a high-side hose-cut-off switch wired in-line to the 12V wire that engages the compressor clutch to keep the pressure from spiking.....

 

[94blue]

Thanks. I'll keep that in mind. Think I'm going to borrow another set of guages to make sure my high side guage isn't way out of wack. 400 PSi just seems unbelievable.

Should you check pressure at idle or cruising speed...which in my case would be about 2300 RPM?

 

[adsm08]

Pressures are checked at idle. 400 PSI can be correct depending on the temp.

 

[97RangerXLT]

100 degrees is pretty hot, that a/c unit has to work pretty hard. The only other reason you might get abnormally high pressure is that something is in the line that is plugging the expansion valve/ orifice tube. generallly that can come from parts of your old compressor still in the lines or the lines themselves.

Did you flush the system thoroughly before putting it together? if not, it won't take long to trash your new compressor. if you don't flush it, you should at least put an inline filter to catch the crap before it goes into the condensor/ compressor.

AJ

 

[94blue]

It may have been hotter than 100. We topped out at 111 today (115 tomorrow...yikes!). I think I'm going to take another look at this in the morning. I may have over charged it. I was under the notion you wanted to see around 45 psi on the low side at idle. What I've been reading tonight indicates 35 would be more like it.

 

[97RangerXLT]

I believe you want to charge your system by amount of refrigerant and not the pressure if you can. with a system with all new parts and no refrigerant in it you can do it. I believe you want 18 or 22 oz of refrigerant from an empty system, and that is considered fully charged. I think Adsm can chime in on the actual amount, but I would only charge by pressure on an older system that is low on refrigerant (chances are it will leak out anyways in such scenario..)

with 111 degree temps and an overcharged system, yep, that can give you extremely high pressures.

My truck has the same problem, after 13 years of life and about 130k on the engine, the a/c quit blowing cold on me. compressor was cycling rather quickly so I figured it needed a boost of refrigerant. I hooked up my gauges and the high side went past 350 psi on a day in the low 80's. and then blew the line off of the High side valve on my gauge set. So I figure the expansion valve or orifice tube is blocked with debris from a slowly deteriorating compressor or lines. So at the time I did not have the money for an a/c rebuild and said fugg it and drove it for the past few years without working a/c and a nonworking passenger window. that sucked... I have now bought all of the items I need for a complete A/C rebuild. Stay tuned, I will put together a How-To when I start it.


AJ

 

[94blue]

I would have much preferred to weigh the charge in but like so many DIY's don't have the scale or 30 LB jug and have to get by with the 12 oz cans. I figure I put about 23 ozs in today if you eliminate a bit for clearing the hoses. Maybe I am overcharged.
Wish I would have known about in line filters before installing the compressor. Only $10 to $20 at the autoparts store and a snap to install. To late now but if I have to evacute the system again I'll put one in for sure.
My '94 Short Bed XLT is on it's 3rd compressor now. Had the system rebuilt at the shop 10 years ago, I replaced a compressor about 4 years ago and yesterday did the compressor, acum. and orifice tube replacing all o-rings as i went. Orifice tube was all clogged up with oily gook but no signs of metal or debree. Probably should have flushed it but sorta ran out of money to buy tools and chemicals with ;>) Hope i don't end up regreting that.

 

[exbass94]

You can charge by weight using the 12 oz cans and a postage scale. I did it once, it worked great.

 

[94blue]

You can charge by weight using the 12 oz cans and a postage scale. I did it once, it worked great.

Figured it out this morning. A 12oz can= 3/4 pound. 2 cans= 1/1.2 Pds 3 cans =2 1/4 pds. etc. My system label states 1.7 pds max charge. That works out to 2 full 12 oz cans and about 2 ozs of a third can. CLOSE ENOUGH!

 

[94blue]

Found out this morning that the head pressures were so high because my fan clutch is shot and needs to be replaced. When the engine is cool the pressures are good but as things start warming up the head pressure climbs rapidly. A little water sprayed on the condensor brings the readings right back down. Already bought the new clutch and will be changing it tomorrow morning.

THANKS, EVERYONE, FOR YOUR HELP WITH THIS.

 

[adsm08]

I believe you want to charge your system by amount of refrigerant and not the pressure if you can.

Actually, there is no way to properly charge the system except by mass of refrigerant.

 

[adsm08]

Found out this morning that the head pressures were so high because my fan clutch is shot and needs to be replaced. When the engine is cool the pressures are good but as things start warming up the head pressure climbs rapidly. A little water sprayed on the condensor brings the readings right back down. Already bought the new clutch and will be changing it tomorrow morning.

THANKS, EVERYONE, FOR YOUR HELP WITH THIS.

That will do it every time.

 

[94blue]

Replaced the radiator fan clutch this morning and sure enough the the head pressure is in range now that the proper airflow is being pulled through the condenser coil. Noticed the engine is running a little cooler now too (imagine that!).
Makes me wonder if the bad clutch is what led to my compressor shaft seal leaking in the first place. As I said earlier, I saw the high pressure gauge hit 400 PSI at one point. Thats a lot of pressure for those seals to deal with.