1999 E300 AC question - PeachParts Mercedes-Benz Forum

dhake2 · #1 06-09-2016, 10:43 AM

I hope the W210 AC guru's can help me fix my AC. Last fall, my compressor failed so I bought and installed a new compressor, condenser, dryer, expansion valve and comp-cond hose, cond-dryer hose and dryer-evap hose. I flushed the evaporator and hose then I poured out oil from new Denso compressor and added 8oz of new oil to compressor and charged the system. The system works when the outside temps are in the 70's but stops working when temps get hot. The fans are working. I am not throwing any codes and don’t recall what my gauges where reading (I can re-check this weekend) but am fairly certain the system is shutting off due to high-side pressure getting too high. The compressor is kicking on and off. The #7 sensor cycles from 23-30. I had a reputable shop flush the system fearing some particles didn’t get flushed from evaporator and clogged the expansion valve. The system is still not working when temps get warm outside. Could I have too much oil in the system? Any other ideas???

leathermang · #2 06-09-2016, 10:45 AM

' pretty certain ' is pretty nebulous ... you need to put the gauges on it and report the results first...

tjts1 · #3 06-09-2016, 12:01 PM

Your high side pressure is (23-30bar = 333-435psi) is way too high. The AC is shutting off to protect itself. Remove some refrigerant.

leathermang · #4 06-09-2016, 12:25 PM

I am not sure that ' too much refrigerant ' always equates to high side pressures being too high... too much refrigerant will mean that he differences between high and low side will be too close together.. by definition working against the concepts used to provide cold air....more investigation is needed I think...

Diseasel300 · #5 06-09-2016, 12:37 PM

If the system were that severely overcharged, I'd expect the system to not really work in cooler (70˚) weather either.

Connect a manifold gauge set (both high AND low side) and see what the pressure balance is (you can roughly go by the chart in Post #3 above).

If you're truly overcharged, both high and low sides will be high. If you have a restriction, high side will be high, low side may be normal or low. You can check for a restriction by letting the system build pressure, then shutting the engine off and seeing how quickly the pressures start to equalize.

If you're reading high side pressure through a sensor or transducer, it's possible that the sensor itself is the problem. Manual gauges will show you exactly what's going on and remove any guesswork from the equation.

dhake2 · #6 06-10-2016, 10:05 PM

Thanks so much for everyone's help. This forum is great. I hooked up my gauges this evening and it was 95 deg outside. The compressor was cycling on and off with the high side pressure cycling from 350-450psi and the low side cycling from 70-80psi. Keep in mind the system has been vacuumed and recharged twice so I am confident the system is not overcharged. I have a brand new Denso compressor, condenser, dryer, and expansion valve. Clearly my pressure is too high. Where do I begin to troubleshoot and fix this? Thanks in advance!!

Diseasel300 · #7 06-10-2016, 10:11 PM

You are way, WAY overcharged! Ideally take the car to an indy shop and have them recover and weigh-in the correct refrigerant charge. I've had this done on my last 2 cars and was usually less than $50 each time I had it done. I have the equipment to do it myself, but Hondas are picky TO THE OUNCE (17 oz for a full charge) and my scale/patience aren't that accurate!

The fact your suction line pressures are so high is a massive clue that there's simply too much refrigerant in the system. If you had a restriction, they'd be much, much lower. The compressor is cycling on high-pressure trip to keep it from grenading itself or the condenser. Continue operation at your own risk!

Deplore · #8 06-10-2016, 11:55 PM

I will echo what others said....You are seriously overcharged. #7 on a.c. Control on my car reads 7-15 and I have nice cold air at all time.

Seriously, man.

dhake2 · #9 06-11-2016, 02:05 AM

The thing is I charged it the first time with a professional AC scale and then took it to a competent Indy who recharged with the exact same results. Indy thinks restriction.

Diseasel300 · #10 06-11-2016, 10:57 AM

Quote:

Originally Posted by dhake2

The thing is I charged it the first time with a professional AC scale and then took it to a competent Indy who recharged with the exact same results. Indy thinks restriction.

Find a new Indy.

Assuming the charge were correct to begin with: If you had a restriction, low side would be below normal and high side would be above normal. For example, you'd see the head pressures you're seeing, but the low side would be low (< 15-20 PSI). This applies to just about any sort of restriction in the system. Usually too much oil in the system will show up as a restriction.

If the compressor weren't pumping properly (say it's worn out or leaking internally), your high side would be low and your low side would be high since it wouldn't be capable of building enough pressure or pumping down the low side quickly enough.

You can also have high head pressures if your condenser is blocked with dirt or your fans aren't moving enough air across it. However, the pressure won't be as high as what you're seeing, and the suction line pressure is usually elevated, but nowhere near as high as what you're seeing.

All signs point to overcharging.

leathermang · #11 06-11-2016, 09:29 AM

What refrigerant are you using ?
The oil that you did install was what kind ?
The oil that you did install was put into one place only ? The compressor ?

jay_bob · #12 06-11-2016, 09:34 AM

Just confirming, the proper charge for a W210 is 1 kg or 2.2 pounds.

The chart posted above relates to parameter 7. The high side kPa number divided by 100 converts to bar which is what is shown on the CCU.

I think it is odd, the pressure is in bar but the temperatures are all in degrees F on the CCU parameters.

Or just use the quick and dirty method: from parameter 7 to PSI multiply by 15. 1 bar is technically 14.7 psi, but since you are dealing with low resolution, multiplying by 15 is within the margin of error and easy enough to do in your head.

I concur with other posters, after my rebuild, the normal range for parameter 7 (high side pressure) is in the mid to high teens, parameters 3 to 5 (left/right heat core and evap temperatures) in the low to mid 30s, and parameter 8 (refrigerant high side temperature) is in the low 100s. I have never seen my high side pressure go over 20 (300 psi). This all on a 90+ degree day in Columbia, we have officially hit summer here already. It is supposed to be nearly 100 tomorrow, it will be interesting to see how it does.

Did you change the pressure and temperature sensors when you replaced the dryer?

dhake2 · #13 06-12-2016, 08:52 AM

UPDATE: It was 90 deg yesterday and I hooked up the gauges before starting the car and the pressures on low and high side was reading 120. I relieved the pressure down to 100psi and started the car. The pressures are now 35/325. The vent temp is about 50. I could live with this if I am not damaging the system. I am wondering if I have too much oil in the system. I originally charged it with 2.2lb of r134 and 8oz of pag46 oil assuming the system was completely empty. The evaporator was the only part not changed but I flushed it but may not have gotten all the oil out. Thoughts??

I am so appreciative of all the help offered on this.

leathermang · #14 06-12-2016, 12:13 PM

Quote:

Originally Posted by dhake2

UPDATE: ...... The vent temp is about 50...... The evaporator was the only part not changed but I flushed it but may not have gotten all the oil out. .......

Ok.. just for consistency when comparing vent temperatures... they should be quoted with the windows down, the blower on LOW and sufficient air being supplied to the condensor... they will read higher when the blower is not on low... but will cool the car quicker..
You flushed the evaporator.... could you EXACTLY describe the steps and conditions you engaged in to do that ? You took out the TXvalve if you have one, you put some type of liquid flush through it , you did that until what was coming out was clean looking ? that sort of description....

funola · #15 06-15-2016, 05:42 PM

Quote:

Originally Posted by leathermang

Ok.. just for consistency when comparing vent temperatures... they should be quoted with the windows down, the blower on LOW and sufficient air being supplied to the condensor... they will read higher when the blower is not on low... but will cool the car quicker..
..........

What is the reason for blower on low? Most AC sites recommend blower on high and system in recirculate mode, windows down, doors closed so you can reach in easily to feel the vents.

Below copied from Troubleshooting with Gauges FAQ

"Should I test with doors open or closed, high idle, blower on high or low?
We should measure high and low side pressure at stable engine speeds. This can be done at engine speeds just slightly above idle. 1,200 to 1,500 RPM is most often recommended. On front wheel drive cars, never rev the engine or hold the engine at high RPM while charging or checking pressures. This can create dangerous high pressure. This is because electric condenser fans are fixed in speed, and will not compensate for high engine RPM. The same holds true on rear wheel drive cars with engine driven fans. A defective fan clutch could cause pressures to reach dangerous levels at higher engine RPM.
We like to test with the system in MAX position on high blower with doors closed. Windows can be open. MAX (recirculate) mode is preferred since we'll need to have the hood up while charging and testing. In fresh air mode, hot engine heat can be drawn into the fresh air cowl under the wiper blades. Same reason we would like to test with doors closed. We would like to keep engine and exhaust heat from causing abnormal heat load on the evaporator. We're not bothered by having the windows down, since this helps create a typical and stable heat load. And it's easy to reach in and feel how cold the vent temps are getting.
Testing should be done with blower speed on high. Low blower speed will reduce heat load on the evaporator to the point where compressor cycling can occur. We want nice stable conditions when testing. When needed, low blower speed can be used to force low side pressure down during testing and adjustment of compressor cut-out pressure."

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