New compressor still no A/C
 

87 300E, The compressor failed. I replaced it with a re-built from AutoZone along with new receiver dryer. Took it to a local shop to have it flushed, evacuated, and filled. They fill it 34 oz of R12 and it doesn’t cool. They tell me the gauges show no real pressure difference between low side and high side with compressor on and clutch engaged. Their summation was bad compressor (defects are rare, but possible) because the freon is not being moved through the system.

I get the replacement compressor; they install it and still no cold air. Now they tell me the original compressor has left debris all through the system clogging things up. I asked if any trash was visible during the flushing process. No real answer to that question.

Are there any electrical functions that could be preventing the cooling process if the clutch and compressor seem to be working? Clutch is definitely engaging, and I can’t imagine two consecutive defective compressors.

Could there be issues with the klima relay or other switches and relays? Or is my clutch engaging a sign that these are in working condition

Any suggestions?

Other facts
In dash push button controller less than 6 months old
Holds pressure, no leaks
Blower works fine

Might be a bad expansion valve , We sell a lot of expansion valves for that car here. I'm just a Partsman not a Technician. I'm sure one of the Techs on this forum will be better to assist you. Just wondering what did they charge you for the compressor and did you check out Fastlane here on this site ?

I was wondering about the expansion valve, but I would have thought you wouldn't be able to get a full charge with a bad valve. I to need information from someone technical, but I think they are replacing the valve today.

I didn't even know about this forum or Fastlane until after I got to where I am now. I wish I had known this looks like a great place.

AutoZone charged me $342 for the compressor and $49 for Rec/dryer.

Iam no tech but Iam supporting the expansion valve diagnosis.but I am also wondering why if they the shop flushed out the system, why there is still debri in the system?

Thanks for the input starfighter. From what I can tell there is a common problem with tephlon coated rings in these compressors. Sometimes when they fail they coat the entire system with the tephlon, burned oil, and aluminum. The coating hardens up and is sometimes not affected when flushed. It then becomes mobile again when the system heats up, thus relocking the system.

I got this from the do it your self section on A/C control diagnostics from this website.


http://www.peachparts.com/diy_stevebfl_0.htm

The climate control/AC control in these cars isn't a simple on/off system -- they have "smart" relays an controllers.

There are several possibilities:

No freon in system due to large leak

Defective expansion valve (cool but not cold)

Stuck heat valve, so the AC is working but the heater core is hot, too.

Are you sure the compressor is actually engaged, not just engaged for a few seconds then shut off? These units have a speed sensor, and if you have the wrong unit, the Klima relay shuts off the compressor after a few seconds. The 300E compressor is NOT the same as any other, and there may be model to model differences as well as year to year -- if the wrong one is installed, it won't work since the relay gets the wrong signal.

Working pressure should be 30 or so psi on the suction side, 300-400 psi on the hot side. You can check easily -- the suction hose should be cold and have condensation on it, the hot side should be almost too hot to touch. If not, the compressor isn't compressing or isn't running.

My indy mechanic has had fits getting functional rebuilt AC compressors, and any failure is always due to "dirt in the system" -- he installs a filter in the suction line. This is a dodge to sell crap rebuilds and deny warrenty (the latest swindle in the auto parts business).

My guess is a compressor/Klima mismatch -- do you have the number off the original compressor? You cannot just change the sensor, either, the relative speeds must be correct. Big pain. The mechanics have absolutely no idea how this system works, and since the compressor initially kicks on, they think it is fine. Find out which compressor you should have, and what was installed, and if they are different, get the correct one. May solve your problem. Also, do you have the original pulley on the compressor, or did you get one with the replacement? The wrong size pulley will do the same thing.

Also, high/low pressure switches can fail, so no compressor clutch engagement. Clutch can get oily or be out of adjustment and not turn the compressor, which will cause the relay to shut off, too.

Check auxillary water pump operation, too -- if it is stuck on, you can get excessive heat, making it look like the ac isn't working.

Not fun. I wish MB would sell the simple AC systems -- I don't mind setting the temp and function manually, saves a whole lot of hassle just to keep the car the same temp all the time!

Peter

Psfred, thanks for your input. The freon is holding with no leaks observed. Leak check was installed no leaks seen plus the fact the gauges show pressure. The clutch is engaging, and stays engages until I push the button on the control panel.

There is no cold air it is nothing but hot air at any rpm. As you can see others have suggested the expansion valve also. If I am not getting any cold air period does this mean my problem is more than just the expansion valve?

As far as the correct compressor, I believe it is, the parts store gave me three parts number (OEM) to look for on the original compressor. I was able to get the full number to match it to the “correct” replacement. At least according to the books at the part store.

Your point about all the relays is part of my question. The mechanic says the system shows no movement of the freon. This determination was made based on gauges measuring the high (100 psi) and low side (85 psi) simultaneously. The gauges didn’t really change with the compressor off and clutch disengaged compared to when it was on with clutch engaged. It was this no measurable change in pressure from either side while the compressor and clutch was running that lead them to tell me the first compressor was a “defect. With the new (rebuilt) compressor the system is doing the same thing. With over 2lbs of freon the gauges don’t detect any freon movement. Their summation is blockage of all devices from the trash that can’t be flushed out.

Sorry for the long winded comment, but this is my main question is there anything electrical that would prevent freon moving through the system provided the compressor and clutch are functioning properly?

If this is the case wouldn’t I be able to check this by running the fan (no /AC) on vent on a cool night. It should blow outside temp (roughly). If much hotter than this it would indicate aux pump creating heat. Is that a correct assumption for a cheap test?

Thanks again for everyone’s suggestion. There are a couple other smaller issues that was leading me to believe I should sell the car, but after seeing this sight you guys have me motivated to get this big A/C problem taken care of and work through the smaller issues a keep the car.

If the AC system is plugged anywhere but the suction inlet of the pump, it will shut off due to high pressure, since all the freon will be stuffed into the high side. I've blown a hose from just this on the Volvo -- orifice tube completely plugged, and boy, was that a devil to get out!

Sounds to me like an open expansion valve! 85 psi on the suction side and 100 on the high side indicates no restriction in the AC at the evaporator, or a seriously defective pump or wide open bypass, if there is on (not that I know of, anyway!). More like the needle on the expansion valve is broken off, actually! Must be one hell of a hole in there for there to be no pressure drop -- the volvo orifice tube is about 2mm diameter and about 1 1/2 inch long -- gives 300 psi high side, 35 psi low side at idle!

The expansion valve is up by the brake booster, down low. You can trace the lines up there and see it. It should consist of a block with two lines attached (big and little), a block with a little diaphram thingy on it, and another block (the evaporator, actually).

The air shouldn't be warmer than outside if the temp control is set all the way cold (shuts off re-heat). The temp control valve can fail wide open, causing excessive reheat, and keep the expansion valve wide open. I would suspect this if the air is actually hot. Be warned, failure of this valve can trash the pushbutton control unit! You can check this exactly as you have described -- if the air coming out of the vents is significantly warmer than the outside air, it is being heated, ergo the valve is open.

Check the temperature of the AC lines -- if the suction side (large hose) isn't cold or cool, something is seriously wrong with the compressor or the valve is missing or broken in the expansion valve.

It isn't too difficult to change the expansion valve EXCEPT that the screws are small and easily stripped, and there is no way to stick a driver in them and give them a whack to start them -- firewall is in the way. Have a mechanic do this! Expansion valve is cheap ($40 or so!).

I'm still mystified at how there could be such a small pressure difference if the compressor is actually turning!



Peter