Recently purchased a 91 SL300, and sorting through a few issues.
The only major one seems to be the A/C.
Worked "okay" when I drove it 200 miles home last weekend, but gradually getting less and less cool this week (it's 98 degrees this week, so I'm asking a LOT of it, granted) :-(

Figured I'd check the freon pressures (it's already been converted to R134a), and all I can get the gauges to read is about 105psi on both the low and high sides with the a/c on.
Any possible reasons or things to check for why I'd have no differential in comparing low and high-side pressures??
Thanks,

__________________
Barry

bad expansion valve?

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The compressr is not kicking on. Test circuit.

Good luck,

Compressor not running = Bad speed sensor.
Compressor running = Bad reed valve in compressor.

(Above not absolute but probable.)



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[http://languageandgrammar.com/2008/01/14/youve-got-problems-not-issues/ ]

"A liberal is someone who feels they owe a great debt to their fellow man, which debt he proposes to pay off with your money."

Doh!! Sometimes I amaze myself - in a NOT so good way!! :-(
The compressor wasn't even turning......

But at least we now need to check the speed sensor, but....
Where the heck is THAT??
I've traced the brown and yellow/green wire back into the electrical "guts" of the corner of the engine bay, but don't know what I'm looking for there, and lose track of those two wires into THAT maze....

Regardless, I figured I could short the brown to ground and the yellow/green to a 12v source, and I'll hear the clutch "clicking" like it WANTS to engage, but not much engaged movement. Also, while the car is off, I can turn the compressor by hand, for what that's worth. The compressor seems to spin relatively freely (I expected decent resistance), just that the electro-magnetic clutch doesn't seem to really try to "engage" with authority.
So, bad clutch, or bad clutch/compressor unit, or???

Thanks,

__________________
Barry

With the engine off, jump 12V to the clutch and see if it clicks. If it does not, check the clutch coil with an ohmmeter and see if the coil is open. If the coil is not open and it is still not clicking in, then check the air gap.

If the clutch kicks in when jumping 12V to it, then you need to see if the low pressure switch is making contact. Use your ohmmeter to check it.

Good luck and let us know the outcome of these tests. I believe that these tests should be done before worrying about the rotation sensor.

Good luck,