I am trying hard to learn and DIY this 1991 Mercedes 190E 2.3. The car is still alive after all these years but i do want to keep the labor costs down by doing it myself. I'm very disappointed the Service Manuals are horrible unlike my 2002 Dodge Caravan and so i turn to you guys once again....
The issue this go around is the A/C. The unit just does not blow cold air. The blower motor is fine and it certainly blows heat when set but the cold air never works continuing to blow warm air. It all used to work. I do recall many years ago we took in the vehicle to have its freon? topped up due to some slow leak. Perhaps this is the same issue?
Can you please provide an intermediate noob a quick guide on what to inspect to conclusively determine the fault with my A/C not blowing cold air.
check to see if the compressor clutch engages and rotates when the system is placed in A/C mode with engine running. If compressor clutch does not engage, put a set of the correct gauges (R-12 or R134a) on the system and check for the correct pressure (at your ambient temperature condition). You'll be able to tell which refrigerant was last in system by type of gauge connector; i.e. if its a Schrader fitting it's R-12. Temperature/pressure tables can be found online for the refrigerant that is in the system (R-12 or R-134a).
If no pressure is indicated; you can locate the low pressure switch (normally on or near the filter/dryer), disconnect the connector and place a jumper across the connector's terminals to see if the compressor operates in A/C mode; only run compressor in this condition for a few seconds (long enough to determine clutch engagement and that there are no unusual noises).
If clutch engages and compressor operates normally, then the system is low on refrigerant and likely has a leak that requires attention.
At this point you could charge the system with one can of refrigerant containing an indicator dye and operate system to locate the leak(s). Follow all recommended safety procedures when performing this diagnosis/work. Most leaks will either be at the O-rings located at junctions between hoses and fittings within the system or within the hoses themselves, if you're lucky. Leaks can also commonly occur within the condenser or evaporator and at the compressor shaft seal.
Above all, you need to locate and eliminate any leaks. Depending on your expertise, the replacement and/or repair of system components can be accomplished by a DIY'er with the aid of posts on this site as well as others. All components and compressor rebuild kits are readily available.
check to see if the compressor clutch engages and rotates when the system is placed in A/C mode with engine running. If compressor clutch does not engage, put a set of the correct gauges (R-12 or R134a) on the system and check for the correct pressure (at your ambient temperature condition). You'll be able to tell which refrigerant was last in system by type of gauge connector; i.e. if its a Schrader fitting it's R-12. Temperature/pressure tables can be found online for the refrigerant that is in the system (R-12 or R-134a).
If no pressure is indicated; you can locate the low pressure switch (normally on or near the filter/dryer), disconnect the connector and place a jumper across the connector's terminals to see if the compressor operates in A/C mode; only run compressor in this condition for a few seconds (long enough to determine clutch engagement and that there are no unusual noises).
If clutch engages and compressor operates normally, then the system is low on refrigerant and likely has a leak that requires attention.
At this point you could charge the system with one can of refrigerant containing an indicator dye and operate system to locate the leak(s). Follow all recommended safety procedures when performing this diagnosis/work. Most leaks will either be at the O-rings located at junctions between hoses and fittings within the system or within the hoses themselves, if you're lucky. Leaks can also commonly occur within the condenser or evaporator and at the compressor shaft seal.
Above all, you need to locate and eliminate any leaks. Depending on your expertise, the replacement and/or repair of system components can be accomplished by a DIY'er with the aid of posts on this site as well as others. All components and compressor rebuild kits are readily available.
Excellent advice and should be helpful to the OP. One minor point, the Schrader valve is the actual valve inside the fitting, and both R12 (Freon) and R134a (Suva) fittings have Schrader valves inside them. Interestingly, car and bicycle inflation fittings have exactly the same valves inside them as AC systems, but the composition of the seal itself may vary.
An easy way for the OP to tell if he has R12 fittings is that R12 fittings have a male thread, while R134a fittings are quick disconnect type. When a system is converted from R12 to R134a all fittings are supposed to be converted to the proper quick disconnect type, but many shops do not follow the law.
Edit: All M4Hand's advice is good. Don't be tempted to try and take the easy way out and throw in a can of some magic juju juice. That sealant will fail in short order and take your compressor and drier with it. Possibly gum up the expansion valve too. Bad stuff!
What's more interesting is that the valve design predates almost all modern standards...they were originally designed for diving helmets in the 1840's. The thread for the cap is .305in x 32tpi. The thread for the core is .209in x 36tpi. I can't imagine how they ended up with these measurements, but that's how they've been made for more than 150 years.
What's more interesting is that the valve design predates almost all modern standards...they were originally designed for diving helmets in the 1840's. The thread for the cap is .305in x 32tpi. The thread for the core is .209in x 36tpi. I can't imagine how they ended up with these measurements, but that's how they've been made for more than 150 years.
Hmmm, does make one wonder. Like wagon or chariot tracks ending up being railroad track gauges, things may have surprising origins.
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