Too much 134A ???
 

If i put in a little too much freon in will that cause the high side to get hot enough to switch on the fan or is it just that hot out? I'm working on two MBZs, the 280 SEL and a 240D. Hard part is the cheap 134A kits don't have the right fitting for the high side. The 240 is just not that cold of air coming out of the vents. I just had to add a touch of freon the the 280 SEL(Euro).

Any ideas?

Over Charging The System
 

Over charging the system will cause a higher head pressure and your system could blow at it's weakest point. Remember you mentioned retro fit. I take that the system was designed for R-12 which runs at a lower pressure than R-134a to begin with.

Hope This Helps!

Yes, it IS that hot out. I have no experience with converted cars, but my R12 cars? The fans will come on just idling in the driveway.

BTW, technically it is pressure, not heat, that trips the fan switch for the AC.

Too Much 134A???
 

On my recever dryer the feon does communicate with the freon directly. The sensor just mount to the dryer. I have a new switch and dryer, interesting enough the switch does not fit it. Small diameter threaded hole on the port and a larger diameter thread on th sensor. These ar parts that I've had in storage for years. The reciept is still in the box. They will fit something sooner or later. I think maybe I should deplete some of the freon out.

I just want to be cool, oh yeah way cool......:laugh3:

Just a thought here,

Since I still have R12 on hand, I haven't converted a car to R134A yet. But, I thought that the high pressure switch on the drier/receiver had to be changed to one with a higher cut-off pressure, since the R134a operates at a higher pressure.
Is your compressor shutting off too soon, or is it operating and not cooling very well.
Also, it was my understanding that the system requires approx. 80% of R134a compared to R12. So, if the system is overcharged with R134a, this could be your problem.
Please post the fix to your problem.

Good luck,

Dave

Actually, it's the opposite problem. Retrofits are required to have a high-pressure cut-out switch, and your R12 system probably only has a low-pressure cut-out.

I did the 240D first as the system was apart for an extended period of time. I vacuumed the system for ever and filled it with the cheapy Walmart conversion. The first can went in ok, the second died during the install. I then used my gauge/manifold set to top it off. The cooling fan seamed to come on after only running a few minutes, leading me to believe the presures on the high side are just a bit too high. Cooling was not adequate during warm temps (95 degreees +). I thought the Walmart stuff may have had too much oil and it was plugging or semi plugging the condencer. So yesterday I isolated the condencer and gave it a good flushing out with alcohol and gave it a good mlow dry. Vacuumed down the system again and added about two and a half cans. The fans still come on pretty soon and really not cooling as well as it should. I bled out some freon this morning and it's plenty hot out now. I'm makeing a trip to the hardware store and I may let out a tad bit more and see what happens.

Hoping for a cool ride:)

What does that mean?

The fan temp sensor is just that, it activates on temperature not the acual pressure. I noticed that once an a real hot day engine idleing the fan cam on, without the AC system being conected. Must have been pretty hot ambients under the hood that day.


Just got back from the hardware store Temp outside is about 100 deges. System seems to be putting out cooler air, no fan activated and more HP (for a 240D).

I don't know about your car, but on the 124/103 there are two sensors. One is in the head and it activates the fans to run on high speed based on temperature. The other is on the drier and activates the fans to run on low speed.

Any AC sensor on the drier which commands the fans to run is a pressure switch.

Of course, higher pressure equals higher temperature so in the big picture the effect is the same.

Since pressure and temperature of the refrigerant follow a relatively continual relationship in the range of the P/T curve where we are interested, either/or has been used to measure when to "throw the switch" to the aux fan(s).

The original receiver/dryers had an orange switch with a 6mm thread. These measured refrigerant temperature (corresponds to pressure, remember;)) and were NOT in contact with the refrigerant. You could replace the switch with no refrigerant loss; but most have these have been replaced with the newer R/D that has a red switch. There is a green switch also, but you don't see many. They were used for new R/D with old R12 for a short time, I believe.

The new switch is a 9mm thread and goes into the refrigerant and measures refrigerant pressure to turn on the aux fan. Remove this switch on a charged system and you get a surprise. I'm going by memory on the dimensions, but I'm close. Should be verified.

In 1985 (I think) another switch was added to the thermostat housing that works on coolant temperature, as well, to activate the aux fan. One reason for the Klima relay? in this year. Maybe ;) ?

if you are trying to get cold air with 134a in those systems you better clean black paint off condensors and make very sure that the fresh air doors are closed.

I must disagree. I convertered my w126 over to 134-a and it cools down to a very comfortable 42 F degrees at the center vents and my get cooler if I close the rear vent. :)

As far as switches thier are two on the dryer a Temp and a Pressure switch. I kept the original R-12 switches and have not experienced any problems with the A/C funtioning correctly.

The reason for the vehicle not achieving a cool enough temp maybe caused by a clouged evaporator. The older cars did not have a pollen filter and lord knows what has made it's whay in their through out the years.

I thought they were both pressure switches. One high pressure to turn on the fans and one low pressure to prevent compressor engagement if there is inadequate refrigerant on board.

The one on the side of the dryer is the pressure switch that activates the clutch on the compressor and to change the system needs to be evaccuated.

The one on top is the temp switch that activates the aux fan which does not require emptying the system to change. Thier is also a dual temp switch that is located at the thermostat housing that kicks in the aux fan when coolent temp gets too high. :)