A/C Somtimes It Works Somtimes Not - Benzworld.org

mgbaird · 04-15-2003, 12:01 PM

A/C Blows cold at times and at others just hot air. I can turn the car off and start it and most of the time it will blow cold air, and then as I'm driving it will just go back to hot air. Also I just replaced the radiator and thermostat but it seems that it still getshot never redlines but when the car is turned off and sits for a while, start it, almost to the redline> I need help Thanks for any that I receive

1988 300CE

cracker928 · 04-15-2003, 03:01 PM

Pardon my ignorance, but I am a little fuzzy headed from doing taxes last night. Three hours of sleep and all that...

It sounds as though you have two problems first the car is getting hot, and second the A/C does not work so hot[:o)].

If your ratiator is getting hot beyong the normal operating range, then the heat will be transferring to the condenser in front of the radiator. This is the part that removes heat from the A/C system and its ability to do so will be compromised by excess heat.

The intermittent problem can likely (I am inferring) be linked to your engine temp. Stop lights, it does not cool, but as you accelerate and get cool air flowing through the engine compartment, the cooler the cabing gets. Does any of this sound familiar? Let me know if I am close...

You would be well advised to take care of your overheating problem, even if it is not boiling over. Check the fan clutch when the engine is warm (not running) give the engine fan (the one between the radiator and the engine) a whirl. There should be resistance, and it should hardly move. Also check the auxilary (electic)fan out. If the fuse is ok, and you can sometimes hear it run at high temperatures, then (many mechanics miss this)test the fan resistor (pain to get to) under the abs module on the left side of the car. This allows the aux. fan to cool without over-doing it, as in when the engine is a little hot but not at the level that it needs emergency cooling.

I have some other thoughts on the a/c system if this does not work for you.

mgbaird · 04-15-2003, 03:22 PM

The A/C Seems to work at any temperature. If the engine is real hot it sometimes stll blow cool (not cold). The fan clutch seems to work fine. The aux fan does work but only at extremly high temps almost redline. I am completly baffled on the A/C. When slow driving Heavy Traffic the engine will get hot and when I get into clear traffic the temp comes down. A/C still works somtimes. A/C can be working one moment and quit the next at ant temp of the engine. Again thanks for your reply

cracker928 · 04-15-2003, 03:39 PM

The aux. fan resistor may be the problem, then. The A/C also uses the aux. fan to cool the condensor. The wiring for both the A/C and the engine cooling go through that resistor. It should be something like .2 or .3 ohms, but when I checked mine, it was actually shattered (in my '87). It is a cheap part to get and relatively easy to replace for a contorsionist with an extremely long screwdriver. Look where I mentioned, remove the resistor (one bolt fastening it to the body and on philips head screw at each end securing the wiring), and test it with an ohm meter. My new replacement was at .5 ohm, so I wouldn't worry if it is within the range of the values I have mentioned.

Is the system the original r-12 or has it been converted to r-134? I have heard bad things about the conversions....

If the reisitor is not a problem, have the pressured checked by a competent professional. If the system is overcharged it can also caused high heat and poor cooling.

Mike Etchart · 04-24-2003, 11:20 PM

Does it blow "hot" air, or only "not cold" air?

I recently had my A/C redone (new compressor, dryer, expansion valve, new aux fan switch, recharge w/ r12), and when I picked it up, the mechanic told me to keep an eye on it since it stopped cooling one time as we was testing it. He couldn't get it to do it again, but he thoght if it did, it would likely be the AC relay by the battery.

Sure enough, it would intermittently stop cooling when the AC was on over the next week or so. It wasn;t blowing "hot", but you could tell it wasn't cool air coming through. I ordered the AC relay from Rusty and it seemed to do the trick. You may want to check yours, since it sounds similar to what mine was doing..

GwagenLover · 04-25-2003, 07:58 AM

You have several other areas that you should investigate. One or a vaccumn leak that causes the gate to switch from heated air to cold air. The other area is the computer that controls the tempature. Either can really give you this problem.[8)]
The relay that Mike mentioned can surely cause the problem also. I have had to replace several of the relays in my 124.

~R~ · 08-13-2003, 09:33 PM

Quote:

A/C Blows cold at times and at others just hot air. I can turn the car off and start it and most of the time it will blow cold air, and then as I'm driving it will just go back to hot air. Also I just replaced the radiator and thermostat but it seems that it still getshot never redlines but when the car is turned off and sits for a while, start it, almost to the redline> I need help Thanks for any that I receive

1988 300CE

~R~ · 08-13-2003, 09:36 PM

I have a 1988 300CE with the very similar problem and was wondering if you were able to get yours fixed and if you don't mind telling me what was the problem.
thanks ~R~
[/quote]

[;)]

Braingears · 08-13-2003, 10:33 PM

I had the same problem that you are refering to. YOU ARE LOW ON FREON. As you rev the engine, the compressor is sucking all of freon and tripping the low pressure sensor. This shuts down the compressor to protect it from "running dry". It is reset when the engine is turn off then back on.
"I used to be traving down the highway when the A/C went out. I would actually put the engine in neutral (while doing 60mph+) and restart the engine to have A/C.)
Until you add more freon, don't stomp the pedal. By excelerating slowly, you lessen the chance that you will trip this sensor.
You should only need 1 can. Depending on which freon you have, most A/C places will just add a can for $15-$50.

Chuck

CaliE320 · 08-15-2003, 07:53 AM

Good call Cfowler, I agree but at the same time
according to what they're saying. Their Auxilary fan is only coming on at high speeds. As far as I'm aware I might be wrong but the auxilary fan should be on the minute your AC is on. Maybe they should also change their auxilary fan relay as well as look into a new OVP..

~Cali