Purpose of a/c speed sensor
 

I've had this ac issue for a while now. I originally thought it was air flow. If I'm sitting at idle the ac blows ok cool air, maybe 60° - 65°. Now if I increase the rpm to about 2000 while sitting, it blows colder and I get down to about 40°, but I'm running electric fans so the increase in rpm doesn't bring in anymore air, it just speeds up the resolutions of the compressor. I had to bypass the climate control button because it would not trigger the ac to turn on. There is no power getting to the compressor from the plug, so I wired it to turn on when I turn on the low speed fan or high speed fan. So there is no speed sensor. Does this sound like it's a speed sensor issue or does it sound like the compressor itself is bad. The compressor is a used one because when I had the issue of the ac not coming on with the climate control, I thought the compressor failed so I got a used one then I figured out the latter issue after the fact. Thoughts please. Thanks.

I don't have a clue what kind of car you are talking about but it sounds slightly low on freon to me.

..."Purpose of a/c speed sensor"...

To prevent a compressor overspeed!! When sensed, the comp clutch is released.

Actually it's to sense if the compressor has locked up or if the belt is slipping. If the compressor control unit sees belt slip it disables the ac compressor clutch.

-J

This.



And with the garbage tensioner design of the M103, belt slip happens very easily in hot weather due to the load of the belt with a slightly tired tensioner. OEM only there, Febi is junk.

I have never found idle output to be very good on the M103 cars due to the wimpy fan blade design...but if you are running the aux fan(s) and puller e-fans, this should not be an issue.

Running power direct to compressor is odd, perhaps your MAS relay is bad? Low pressure switch?



What refrigerant is in the vehicle? How clean is the evap, condenser, etc.? 134A is terrible in these, especially at slow speeds. If you cannot procure R12 there, use R152A from your air duster cans. Just multiply your OEM R12 charge by 0.56 for your R152A charge.

The charge should be correct. I'm actually running propane (r290) and it seems 20 times colder than r134. Is it possible the compressor is going out?

I have no clue of the pressure curves of the propane, I just know 152A is basically identical to R12... just needs PAG or syn oil. When did you lack check pressures and/or charge?

Of course the compressor could be pooping out, or leaking bad. I have dealt with both over the years, mainly with leakage (case seals or front seal) as opposed to lack of output.

Vacuumed system, and no leaks and added propane also since it's so cheap. Just checked the belt and it is loose. Could this be the problem? Like I mentioned before, there is very little cooling at the vents unless I raise the rpm. Fans are electric, so no additional air is coming across Rachel

Hey, another thing... are your vacuum pods all good? At least for the fresh air/recycled air door along with defroster? In the W124 I had to pull the dash to replace them all, was about a 10 hour job start to finish. Not too bad.

You should hear belt slipping if loose. A new/good M103 tensioner is really snug, I was surprised. Also you R&R the belt via the alternator on them to keep from killing tensioners.

Maybe the pressures of propane do not work well at idle or you are undercharged. I have no idea. Three, 10oz cans of 152R is about $12 around my area. That will fully charge a W126 which holds 2.9lbs of R12, I think the W201 holds about 2.2lbs like my W124. That would be 1.23lbs of 152A or 19.71oz... so two cans of air duster. :)

Compressor died.