1991 300-SEL

I know I'm out of refrigerant. R12 is in route.

I dealt with this once on an '87 Accord. Hot-wired the pressure switch connected to the receiver-dryer and that engaged the clutch which got a draw going. Charged thru low pressure side. Worked well.

On my 1991 300-SEL, there are 2 wires coming off the pressure switch connection. I disconnected one and jumpered the 2 female ends - set a fan speed - turned on the compressor by way of push button controller(PBC). Clutch did not engage. I know I'm empty and have no plans to actually do this until I have the R12 hooked up and ready to go. Just testing to see if I can get the clutch to engage to get a draw of refrigerant going thru the low pressure side once I have the R12. As soon as I see the clutch engage, I'll pull the jumper wire. I then tried jumpering the other wire. Clutch would not engage.

I connected a voltage meter to each of these wires. One read about 13.6V; the other about just a hair over 1V.

If I had an issue within the PBC, would it stop the clutch from engaging using this hot-wire method?

Determining where the refrigerant went is for later. The unit has been empty for quite a long time.

Thanks for your time.

Generally whenever I charge up an A/C system I charge it up with a can through the low side before starting the compressor up. Never had an issue charging an empty or freshly vac'd system this way.

Should not the R12 can have pressure in it that would be enough to charge the system to a safe start state?

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Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Have you placed a pressure gauge on the system to verify that you are in fact low on refrigerant?

System is empty.

Not sure I understand charging thru low side(suction side) when the compressor is not engaged?

Thanks.

Correction, when I would charge through low side, my systems were never empty. Just low. Low enough to cut out the compressor. I would charge a can in and it would be enough to trigger the compressor to run. Then I would continue charging normally.

I have a vacuum pump now so I just vac down and charge under vac.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

That would do it - an existing vacuum. My situation is different. I'll continue my quest to hot-wire the system in order to activate compressor. Juice won't be here until late Tues. next week. I've got time to dig thru the manuals and figure it out.

Thanks.

If this is just a temporary one time thing....

An easy way to hot wire would be to run your own wires to the compressor clutch coil...inline fuse and tap right to the battery. That's probably far easier than dealing with the factory wiring.

Once you have enough R12 in there to convince the MB system to let it run, reconnect the factory wires.

__________________
Cruise Control not working? Send me PM or email (jamesdean59@gmail.com). I might be able to help out.
Check here for compatibility, diagnostics, and availability!

(4/11/2020: Hi Everyone! I am still taking orders and replying to emails/PMs/etc, I appreciate your patience in these crazy times. Stay safe and healthy!)


82 300SD 145k
89 420SEL 210k
89 560SEL 118k
90 300SE 262k RIP 5/25/2010
90 560SEL 154k
91 300D 2.5 Turbo. 241k
93 190E 3.0 235k
93 300E 195k

Thanks JamesDean - likely the safer way to go.

Click on link:

http://www.startekinfo.com/StarTek/outside/12253/program/ETM/ACCfrom86.pdf

Page 8 of 19 - lower left hand corner of that page. Addresses my original question.

I think my jumpering may have been caddywhompus. Will find out this weekend hopefully and report the outcome.