Thanks everyone, for all the input, will have items checked in Whunters possible issues and check for overcharge.

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benzino

Hello congonatty
Buy or borrow an A/C manifold set.
"leathermang", does have a point.
I am one of the best mechanics in the business, (and modest too).
:gasp: I have over charged several systems, through the years. :shock:
#1. Wrong service data
#2. Bad gauge set.
#3. Tired, prototype work, 90 hour weeks.
#4. Just plain made a mistake; only human.
Mistakes do happen, be happy if your problem is that simple.
Have a great day.

If the A/C system is overcharged, exactly what happens to shut it off - does the pressure or temperature get too high which triggers another device?

Since the whole system is based on changing high pressure fluid to low pressure gas... if it is overcharged ANY then all your resources are not able to be utilized... at first your work off your reserve capacity built into the system .... but when it uses up that something will shut it down.... and other factors may decide whether it is the temp or the pressure which does it.... and it may not be the same every time depending on the ambient temp and humidity....
At a certain point it may also be affecting the TXvalve in the block next to the evaporator.... since temp and pressure are fairly proportional for a closed system.

Got a AC manifold gauge set, need to verify if this is the correct steps to check for freon overcharge on 1989 300e. ( Run engine w/air condition on high for five minutes, connect gauge to low and high side, reading should be 24-34psi low side, 230-275psi high side.)

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benzino

One thing for sure... do not hook up anything without wearing GOOD eye protection ( goggles plus flat face shield is much better)
The pressures are directly related to the ambient air temp... you really need an AC book with some charts and the safety warnings to do this.... I never touch this stuff without my manual on the car fender...
The first time I messed with this stuff was about 1972.. and I hooked the freon can up to the high side.... I accidentally felt of the side of the can ... which was getting very hot.... I was really lucky it did not blow up and blind me....
You also need to know how to evacuate each hose as you use it... and practice with the gauge knobs.... you don't want to lose your R12 ... or get your fingers frostbitten... etc...

Use the books and give it a lot of Respect.
Some thirty years ago I replaced the hose on a van. I was charging the system and a hose blew off. It must have hit me eight to ten times. I though I had meet Ali.
Check all your work and if your don't know find out. This is no place to guess.
If you are trusting the shop make them fix it. If they arn't getting it done roll your sleeves up and get and A/C schooling.
Good luck.
Charlie

Go to your local high school tech center.
Take the class on automotive A/C.
Once you know how to DIY, then do it.
Until then, please do not hurt your self or the car.