A/C Hi/Lo is Batt Volt really Batt Volt

[BrierS]

I know most are sick of A/C questions . . . at the hi/lo switch with EC on the console I get 12.8 volts rather than 13.7 measured at the battery. All other console switches reduce voltage to 0.2. System charge status was just rechecked yesterday and is fully charged (PO converted to R-134). Any suggestions before I turn it over to a shop? I am not qualified and will not get into the pressure components of the system.

PS Compressor ususally does not engage but occassionaly does. Turns freely.

[stevebfl]

If I understand you correctly you have successfully eliminated the push button controller from your problem. You have verified the ground control signal the PBC sends through the lo/hi pressure switch on the drier.

Does your tach work? You are probably dealing with a Klima problem, but unfortunately most klima problems are not fixed with new klima relays. The problem usually is slipping belts, slipping clutches, too low engine speed, bad full throttle switch, too high engine temp, or poor engine speed signal.

[BrierS]

Originally posted by stevebfl
If I understand you correctly you have successfully eliminated the push button controller from your problem. You have verified the ground control signal the PBC sends through the lo/hi pressure switch on the drier.

Does your tach work? You are probably dealing with a Klima problem, but unfortunately most klima problems are not fixed with new klima relays. The problem usually is slipping belts, slipping clutches, too low engine speed, bad full throttle switch, too high engine temp, or poor engine speed signal.

Thank you for taking the time to respond.
Yes the tach is working and has shown no sign of not working since I bought the car.
I didn't know if it was unusual to find different "battery voltages" at the battery and the lo/hi pressure switch. I removed the Klima cleaned and applied dielectric as a routine.
The A/C works periodically.
Defrost has ONLY blown hot since I purchased.
I have eliminated various vac leaks within the engine compartment after replacing the vac pump but am still chasing some.
I have no fear of venturing into electrical and vac but WOULD not get into the pressure portion of the A/C since I have no knowledge or equipment.
Any thoughts as to where I might check (within the areas I am comfortable)?
Though I would prefer to explore and solve the problem myself I will turn it over to a qualified tech rather than chance wasting expensive components. i.e. I know and accept my present limitations.

[stevebfl]

I would remove the Klima relay an jump the 30 term to the 87 term with a fused jumper (with an 8amp fuse).

I would then evaluate the AC as the compressor should be running. If it is not you need to verify the circuit to the compressor and view the clutch gap. The clutch coil should have around 3-4 ohms resistance which can be checked from term 87 (klima) to ground.

If the AC performs then with it running evaluate the other terminals for improper values. Check the full throttle switch to verify it isn't thinking full throttle. It's a little harder but the engine speed signal and the compressor speed signal are also checkable at that point.

And if all thats keeping you from cool air is that confounded Klima system I'd by-pass the thing and remember to shut off the AC when the belt is burning up. The archives will spell out the lobotomy with an "ice cube" relay.

[stevebfl]

BTW don't worry about the small voltage drop from the battery through the Klima it is natural. That is a low current sensor circuit probably filled with transistors and dropping resistors that don't act with no resistance to an unloaded circuit as a normal resistor would.

[BrierS]

Before turning this into a Q&A thread I searched for a schematic on my CD and this forum. After pulling the Klima (001 545 80 05)the pins are labeled differently. As you know, the socket is numbered 1-12 with odd numbers running along the front and even along the back. The Klima has 31, TD, 15, 87, GK+, GK- along the front (odd numbers on the socket) and GM+, VL, 87k, blank, KL, T along the back row (even numbers on the socket).

To jump terminal 30 to 87 with an 8amp fused jumper I can't tell which of my terminals are 30 & 87. No #30 and two 87s (including 87k).

[stevebfl]

Use 15 and plain 87.

[BrierS]

THANK YOU. SUCCESS!!!

Okay, following your advise and doing additional research regarding "ice cubes" my A/C compressor is doing what it is supposed to.

Since I was uncertain about jumping 30 & 87 on the Klima socket because of my numbering being different, I thought of using 5 & 7 on the socket. However, I hate taking too much of a risk. I turned to the ice cube search and learned where they are in my '87 300TD. I pulled every relay out, cleaned and put dielectic on each pin. I switched them around just in case one was bad and others not. Additionally, I searched and repeated the clean and dielectric on every connection I could find. Put the Klima and battery back in, started her and ran through the push button switches as the compressor remained on with all except the EC button. I may still have some minor issues with with some vacc leaks but at least the A/C system is blowing cold again. I'll keep you posted if it remains so.

Thanks a bunch!!!

[BrierS]

Too excited . . . try "following your advice" not advise.