AC not charging

[Exekiel69]

While working on the same car 87 Mercedes 300TD, We decided to recharge the ac system (empty) and switch to r134. I pulled all lines and installed new O-rings, installed new expansion valve, new accumulator, clean lines, etc. I put a vacuum pump on it and let it run for about an hour then let it sit for another hour and check the system and it held the vacuum just fine so I connected the gauge kit on the low and high ports. The ac pump clutch does not engage when You turn the ac ON inside the cab and the vacuum pulled the first bottle but the second one was untouched so I jumped 12v to the pump and made it engage the clutch but it would not pull the freeon at all.
This car has also another problem, while running/driving with the heat on it will switch suddenly with out warning to cold air and then back to heat after a while.
I started reading and found there is a ac relay for this things, could that be the reason it doesn't pull the freeon?
I hate to see this thing not getting fixed but I'm at a loss. Thanks in advance for any help.

 

[The Warden]

Very odd that it didn't pull any freon even with the clutch engaged after you jumped it...to me, that would imply that there's something obstructing the system. I know you cleaned the lines out, but are you 100% certain that both the condenser and the evaporator are clear?

It makes sense to me that the a/c compressor doesn't turn on when you turn the ACC on; there's a low-pressure switch that prevents the compressor from cycling if the pressure's too low (usually below 20 psi or so; certainly an empty system will keep the compressor from cycling). If you get the system up to pressure and the compressor still won't cycle, then there's an issue...either with the low-pressure switch, the relay you mentioned (don't know about that; that's a 124 thing), or the ACC control unit itself.

As to the system switching to cold then back to heat...it's possible the ACC unit's going (specifically, the rheostat, but I don't know if you can replace that by itself), or the temp switch could be on the fritz...I don't know if the 124 has a monovalve like the 123 does or not, but that's also a common failure point, and a repair kit goes for only $15.

I can honestly say that I don't know; I've never torn this deep into an M-B's climate control system. You might want to check out the tech forums on http://www.peachparts.com...

Sorry I couldn't be of more help...best of luck!!

 

[Exekiel69]

I will have to open the system and blow through it again, also after I pulled the high pressure adapter from the hose the needle started loosing freeon, that is the only one I did not replace, it was deep near the grille and I could not see it so I left it alone.
He replaced that temp control panel and it worked fine for a while but now is doing the same thing.
I'm not a pro with ac units but I have done several successfully, this is by far the hardest one I've seen, not what I would call simple.

Thank You for the link, I'll start reading.