One last question about bad A/C - PeachParts Mercedes-Benz Forum

#1 06-21-2002, 11:25 PM

Okay, for a peace of mind and end all this teeth gnashing, is it perfectly safe to drive/operate your car with a bad A/C? My A/C is losing its cooling capability either from a leak or bad evaporator. I don't plan to fix or refill the A/C, nor do I plan to use it at all. Do I have anything to worry about? Thanks in advance.

engatwork · #2 06-22-2002, 07:14 AM

It isn't going to hurt anything but if you ever decide to sell it - it will reduce the value of the car somewhat. It will also require alot of new a/c parts if and when it is put back into service.

400E · #3 06-22-2002, 08:28 AM

You should avoid using climate control settings which engage the compressor, which includes the defroster mode. You never know; you may someday change your mind about fixing the system and there's no point in causing more damage.

That's what I did when my evaporator went out, anyway.

stevebfl · #4 06-22-2002, 10:30 AM

Both real good responses.

You might want to disconnect the low pressure switch to keep the compressor from coming on. Jim's right about letting the system go killing the cars value. Anyone asking me about purchase info on a 300E with no A/C gets a $3000 subtraction on value and a strong no-buy suggestion based upon the concept that anyone that would own a MB and let the A/C go has undoubtably let most everything else go.

As far as I am concerned A/C is only second to brakes as a necessary part of a MB.

#5 06-22-2002, 12:59 PM

I plan to fix the problem eventually, but just not now. My M-B is treated like a princess (still looks new after 12 years), but if the problem isn't pressing, then I'll wait until I have the time and resources to fix it. About the climate control, how do I turn it off? My car is a '90 190E and has that red-blue turn knob. Most of the time it's left on the blue. In addition, the air-vent button (the symbol is two squares side by side) is always depressed. Thanks again for the informative responses.

Ashman · #6 06-22-2002, 05:57 PM

cossie I am in the same boat as you. I have turned off my ac altogether and just open all my windows. I will fix mine soon. I just need to set aside funds to do it. thats going to take a couple of months. though I will attempt DIY on it, I am skeptical of taking apart, well the entire dash of the car and then some.

Steve, where is the low pressure switch you are talking about? I don't want to ruin anything else in my ac either as I will put it back into service as soon as possible.

Alon

stevebfl · #7 06-22-2002, 07:26 PM

The low pressure switch is on the drier. It is the switch without the short wire leads made to it. The other switch turns on the fan.

The problem with letting a leaker go is the accumulation of moisture and the corrosion and acids that get formed as a result.

stevebfl · #8 06-22-2002, 09:47 PM

The low pressure switch effectively disconnects the compressor in the easiest of ways. No tools. Just reach down and pull off one or both wires. The switch cuts the compressor off if the pressure is too low (out of gas) or too high (overcharging or pressure problems such as lack of aux fan).

John Plut · #9 06-23-2002, 08:23 PM

Steve,
My compressor is not coming on at all and I'm trying to troubleshoot the problem. At the low pressure switch, I get 12v at on side and 0v at the other (the switch is open). Does the switch need to be closed for the compressor to run? If so, is a low refrigerant charge a possiblity or is the pressure switch bad?

My initial thought was that even with a low charge, the compressor should come on and if the pressure is too low, it will shut off.

Thanks,
John

stevebfl · #10 06-23-2002, 09:20 PM

The pushbutton controller decides on the need for the compressor based on the sensors and the settings. The signal in most cases is a ground signal. The compressor controller (Klima, MAS, BASE) sees this signal by the control leg being pulled to ground and turns on the compressor (if all its conditions are met). This MOST important of signals passes through the low/high pressure switch.

In your case if batt voltage is on one leg that tells me that the compressor controller is prepared to see the signal. You said one wire was batt voltage and one was open. The switch is closed if there is any gas in the system at all. Check it with an ohm meter or place the batt voltage lead on the switch and see if the other terminal is also battery voltage. Check this with a volt meter as a test light will look like the ground signal and probably turn the compressor on.

If the system has gas on it then place both terminals back on and see what the voltage looks like on either. Since the switch will be closed the same voltage will be on both sides.

With the car running and the system in the EC position (Compressor desired off) the voltage should be battery voltage on both legs of the switch (with both wires in place; pull up slightly and check each term at the base). When the system is engaged (compressor desired on) both sides of the switch should be at about 0.15 volts to grounds. If at any time the voltage is different across the switch then the pressures are wrong or the switch bad (they leak but never go bad electrically).

The pressure switches pur[ose originally was to protect the system from running "dry". At a real low pressuree (this is on the high side so the pressure of any gas will get greater when the compressor engages. In the early 80's the switch was changed from only a low pressure switch to also cut out at high pressures to protect the system from a blockage or aux fan failure. On 134 conversions this is an absolute necessity.

Be real carefull where you might buy this switch as most are only low pressure. The parts procurers see that one number converts to the other and assume they are the same. The early switch is much cheaper. Only the smartest parts houses know the difference. Almost everyone selling this switch has it wrong.

stevebfl · #11 06-24-2002, 07:50 AM

I wasn't sure how fastlane would list it but they should not have the same part number. All MBs from the early 80's till they quit using the switch, need the dual switch.

John Plut · #12 06-25-2002, 11:33 PM

Steve, thanks for the replay.

I checked the pressure switch on my '88 260 with a ohm meter and got infinite ohms (switch is open). There is a possibility that there is no gas in the system although there are no signs of leaks anywhere.

The next question is if the system is low, how can I add R12 if the compressor does not run? On other cars I have owned, when the pressure gets low the compressor cycles on and off so it will at least suck in the R12.

- John