Can overpressurized A/C system cause compressor to fail to engage?
 

1993 W124 300D

Can an overpressurized A/C system cause the compressor to kick off?

I think that may be what my problem is.

I thought I had a bad fuse first but that day was the first very hot day around here.

I checked the pressure and it was over 100psi.

I also noticed sometimes when I revved the engine high the A/C would temporarily stop cooling.

If not, what else might I have going on?

If its hot outside and the AC isn't running the low side can be that high. If there is an overpressure switch it will generally cause a cut out at 400 PSI or so.

-Jason

The pressure? Would that be high side or low side? Compressor on or off?

It read over 100psi with the compressor off but the A/C switch was on.

It actually was pushing 120psi at one point.

I then proceeded to try to bleed off some on the side of the road and ended up bleeding it all off.

I have since been recharging the hell out of it to get it to cool better but this is my first summer with it so maybe that's as good as it cools in the summer.

It has been very hot and uncharacteristically humid here lately as well.

The pressure I read was the high pressure line where you recharge the system.

As I pushed over 65 in my effort to recharge the system, the compressor cut off and will intermittently come back on only to shut off shortly thereafter.

Once, it was running until I hit the throttle, if that's what it's called on a diesel, to raise the RPMs.

I decided to let it rest until I found out more and wasted any more refrigerant.

With the compressor off, the refrigerant pressure varies as a function of temperature. As long as there is a drop of liquid refrigerant in the system, the pressure is constant at a given temp. Static pressure is of little value when attempting to diagnose an a/c issue.

In that case, the system should be evacuated prior to adding new refrigerant. Replacing the receiver/drier is also indicated.

OK, but it's basically acting like it was before I evacuated the system.

Do you have any idea what might be the problem?

You need a good starting point to find out what is wrong. It sounds like you have been arbitrarily adding refrigerant in an effort to make it work.

Recover the refrigerant in the system, replace the dryer, and check for leaks. When you are absolutely sure there are no leaks ( pull a vacuum on the system through your gages, then shut off the valves and leave the gages connected overnight, if the gage readings have changed other than a small allowance for temperature, you still have a leak) Charge the system with the proper amount of refrigerant as (you are using R12 right!) and then you can see if it is operating properly.

An undercharged or overcharged sytem will not cool properly, and if you have a leak, chances are there is moisture in the system, which can freeze in the expansion valve and cause intermittent cooling.

Once you have no leaks, no moisture, and the proper refrigerant charge you can start diagnosing any issues, if you still have any.

Reading between the lines, I conclude:
1. You do not have a set of guages and are reading a single value from the top hose (low side).
2. At this point none of us can estimate what you may have in the system.
3. You need to follow the instructions (short, but not as thorough as others recommend) of the last poster, but first get a complete guage set to be able to connect and get readings on both high and low side as you do this work. You'll also need a vacuum pump.
4. You've got a significant amount of learning (do some searches) before you proceed.
5. You might be better off hiring this done unless you're will to learn how to do this properly.

Answer
 

http://www.id-usa.com/how_to_faqs_recharging.asp

http://autos.yahoo.com/maintain/repairqa/fluids_heat_air_conditioning/ques023_0.html

Automotive repair training book on line, you can download it.
http://www.tpub.com/content/construction/14273/
and
http://www.tpub.com/automotive.htm

http://www.carbibles.com/

Automotive Air Conditioning Systems
http://www.familycar.com/ac1.htm

Aircondition.Com
http://aircondition.com/knowledge_base/Home.html

You can jump the compressor clutch if the system is UNDER charged.
NEVER jump the clutch if the system is over charged..

LOW pressure gauge: When the reading is between 25 and 40 psi with the A/C compressor running, STOP.
The system is fully charged and should be cooling normally.
DO NOT add any more refrigerant.
If the gauge is over 50 psi, you have overcharged the system with too much refrigerant.

High pressure gauge: When the reading gets up around 200 to 225 psi (R12), or 225 to 250 psi (R134a), STOP.
The system is fully charged and should be cooling normally.
DO NOT add any more refrigerant.

NOTE: The high and low pressure readings will vary depending on the system and ambient temperatures (higher temperatures cause higher system pressure readings).


Have a great day.

Additional
 

The Port (Schrader Valve) that is used to "Charge" This A/C system is on the
LOW Side [Larger in Outside Diameter] Hose.
Do Not Attempt to Charge from the High Side Hose.

I'm gonna fall back on CR from Texas's suggestions.

A/C is a "Building Blocks" kind of Endeavor,
You CANNOT "Non-Georgia Tech Engineer" it.

AND from reading your posts,you're a "Short Cut" Kinda guy...

And "Short Cuts" in HVAC work always come back and Bite You in the Nether
regions!

Ok, first off, I am putting in R-34.

It has either been converted or I have been charging the wrong side. I have been charging the side that is actually accessible on the driver side fender well.

This is a '93 by the way.

I don't know when they started coming out with R-34 but this one does NOT have a threaded Schrader valve accessible ANYWHERE but the tires.

If you are using proper charging equipement then you must be useing the low side because the R134a high pressure fitting is a different size (smaller).

-J

"Proper" equipment has valves on both sides. Either or both can be opened to the supply line.

Well, the fitting that comes on the recharge R-34 fits it.

So, either the factory or the person who did the retrofit would have had to get it wrong.

I didn't buy any special equipment and I have been able to recharge the system with oil and refrigerant.

It also cools just fine, now.

I'm still not sure why it stopped cooling the day it did but after replacing the fan fuse all has worked flawlessly.

My concern was that in stop and go traffic it wasn't cooling as well as I had hoped but it also had just started getting very hot and humid all at the same time.

Also, I'm sorry that CI thinks I take too many shortcuts....not sure what he's talking about.

It's R134a, not R-34.

Easy way to tell high side from low side. With the system fully functional, the cold line is the low or suction side. The hot lines are the high pressure or discharge side.

My '97 Nissan P/U came w/R134a from the factory. I'm thinking you could get cars w/R134a in '95.