Hard Shifts with A/C Compressor On
 

I know this subject has been beat to death but I have a specific question with regard to quality of shifts.

I have a '91 300E with 62K on it. From the day I bought it, the transmission shifts were firm but more than acceptable with the A/C compressor OFF. If I simply turn the compressor ON, the shifts become overly hard. I've had to replace the Flex disk recently which was probably caused by the hard shifts.

Can someone rationalize why the A/C compressor would cause this problem and could an experienced technician solve the problem?

Sounds like a vacuum issue caused by a leaking climate control damper door actuator. Not exactly sure if the dash has to come off for the repair or not but that would be worst case. Time to troubleshoot with the MightyVac. Do a search on vacuum leaks.

I agree with Jim -- big leak in the climate control system (can simply be a hose off, for that matter) that lowers the vac when the climate control is on.

Flex disk is a 60,000 mile maintenance item on these cars, by and large -- not in the book, but Hans says 60,000 is about it. He tends to replace them at the 60,000 mile service, nearly always going by then.

Thanks guys. I have a MityVac and found the procedure for testing the vacuum pods.

I have a question. Which of the pods is actuated when switching from *Economy* to *A/C*?

As I said before, this has occurred since I brought the brand new car home. I was reluctant to let the technician at the dealership that sold the car to me to touch it. He screwed up a few things doing basic maintenance so I wasn't about to let him do something more serioius.

I now live near Phoenix and have access to an expensive but good service department.

Shouldn't be any -- they should already be in the correct posistion, the only difference between economy and AC is the compressor is switched on.

However, if there is one moving, it will leak only when the AC complressor is engaged.

Check the vac on the tranny modulator line when the compressor is on vs off -- you may have a vac leak somewhere else, too. My TE runs much lower vac with the AC on due to the load on the engine, I suppose, and shifts a bit harder.

Peter

Yea - I did not pick up on the info about the EC mode versus the a/c compressor until the second reading. I feel confident it is vacuum related. It is just a matter of troubleshooting the system and repairing the leaks.

Assuming this is simply lower vacuum caused by the compressor load on the engine, could the modulator be tweaked to soften the shifts a bit?

Yes it can be adjusted to soften up the shifts. Do a search on here. This has been gone over a time or two. Make sure you resolved the vacuum leaks/issues before adjusting the modulator.