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#1
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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?
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1993 W124 300D -297K on the clock as I type this. |
#2
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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
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1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket Tesla Model 3. 205,000 miles. Been to 48 states! Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels. 2014 Cadillac ELR 2013 Fiat 500E. |
#3
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The pressure? Would that be high side or low side? Compressor on or off?
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#4
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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.
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1993 W124 300D -297K on the clock as I type this. |
#5
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Quote:
In that case, the system should be evacuated prior to adding new refrigerant. Replacing the receiver/drier is also indicated. |
#6
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OK, but it's basically acting like it was before I evacuated the system.
Do you have any idea what might be the problem?
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1993 W124 300D -297K on the clock as I type this. |
#7
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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. |
#8
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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.
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Charles 1983 300D, bought new, 215k+ miles, donated to Purple Hearts veterans charity but I have parts for sale: http://www.peachparts.com/shopforum/mercedes-benz-cars-sale/296386-fs-1-owner-83-mb-300d-turbo-rebuild-parts.html |
#9
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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.
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ASE Master Mechanic asemastermechanic@juno.com Prototype R&D/testing: Thermal & Aerodynamic System Engineering (TASE) Senior vehicle instrumentation technician. Noise Vibration and Harshness (NVH). Dynamometer. Heat exchanger durability. HV-A/C Climate Control. Vehicle build. Fleet Durability Technical Quality Auditor. Automotive Technical Writer 1985 300SD 1983 300D 1984 190D 2003 Volvo V70 2002 Honda Civic https://www.boldegoist.com/ Last edited by whunter; 06-24-2009 at 06:41 PM. |
#10
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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!
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'84 300SD sold 124.128 |
#11
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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.
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1993 W124 300D -297K on the clock as I type this. Last edited by i-osprey; 06-26-2009 at 12:51 AM. |
#12
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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
__________________
1991 350SDL. 230,000 miles (new motor @ 150,000). Blown head gasket Tesla Model 3. 205,000 miles. Been to 48 states! Past: A fleet of VW TDIs.... including a V10,a Dieselgate Passat, and 2 ECOdiesels. 2014 Cadillac ELR 2013 Fiat 500E. |
#13
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Quote:
"Proper" equipment has valves on both sides. Either or both can be opened to the supply line. |
#14
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Quote:
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.
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1993 W124 300D -297K on the clock as I type this. |
#15
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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.
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RRGrassi 70's Southern Pacific #5608 Fairmont A-4 MOW car 13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete. 91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K 90 Dodge D250 5.9 Cummins/5 speed. 400K |
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