Strange Electrical Issue

My '87 328 GTS AC is not working. Clutch has no voltage. Receiver/dryer switch has no voltage. I have taken a look at the relays labelled Z and V in the owner's manual behind the footwell. I removed the one for the clutch, switched on the ignition and jumped prong 30 to 87. The AC clutch engaged. I then took the relay (Z) over to a spare battery and connected it to prongs 86 and 85. Relay clicked as expected. Then I attached an ohm meter to prongs 30 and 87. When I applied voltage to prongs 86 and 85, resistance went from open circuit to 0.7 ohms. So, the relay seems OK to me. The other relay, V, checked out as well using the spare battery and ohm meter.

I checked the ground side of where the relay (Z) is plugged in. Receptacle 85 is not grounded. When I check resistance from 85 to gearshift, meter doesn't register. When I go from where prong 87 plugs in to gearshift, I get a small ohm reading so it's grounded. Seems to me that because 85 is not grounded, relay cannot function as it should.

Lastly, prong 86 has 12 V when blower switch and temperature control are both on. Goes to zero when either is off indicating switches on console are working.

Where should I check next?

 

Thanks for the information and electrical diagram reference. You confirmed my anxiety regarding the switches. Looks like one of the two switches is not working. My suspicion is that the little tube on the temperature control switch has lost its gas. If cabin temperature is low, gas pressure is low and that does not close the switch. If there is a leak, switch cannot close. If possible, I'll spray contact cleaner in the two switches. I might get lucky.

If replacement parts are no longer available, I can install a manual switch in the wiring and control the on/off of the compressor manually.

 

I assume you mean terminals, 85 and 87, the two ground terminals. I'm referring to the numbering on the relay.

 

I'll remove the switch and check it out as you indicate.

 

The temperature control switch is bad. Jumping the two leads at the temperature control switch engages the AC clutch when the blower switch is on and vice versa. Does anyone know where a replacement temperature switch can be had?

 

Once again Steve, thanks for the help.

Getting the top part of the console off was interesting. The 4 switches at the rear of the console top are over 35 years old, and I suspect are brittle. It may have been mentioned before, and everyone might already know it but the safe way to remove the first one is to remove the plastic slot (held on by 2 screws in storage box) that accepts the lock tongue. Then insert a tool of some sort and push up on a switch. As noted in the searches I read, the remainder of the switches can be pushed out with fingers.

 

I need some advice regarding the rolling up of the capillary tube. Below is a picture of the original capillary tube with the retention clip removed. I suspect it is made of aluminum and is wound around a dowel. I would hate to break it. How do I wind it up as shown? Image Unavailable, Please Login

 

Decided the best way to do it is to remove the grommet where capillary passes into the compartment. The hole is large enough for the old coil to pass through thus permitting the new coil to be wound before installation. I can use the old capillary tube to practice on, so I don't screw up the new one. Must remember to install grommet before winding coil.

 

The new switch capillary tube is 2 feet shorter than the old one but will work. I am winding the coil around a drill bit shank. Eight coils done so far. The original one had loops behind carpet/accelerator taking up its extra length.

 

The bean counters are alive and well. The new switch with its shorter capillary tube is more difficult to install. The original one had two 4 inch loops of extra capillary tubing behind the carpet in the accelerator area. The new one has to be taut in order to have its coils butted against the one attached to the expansion valve shown above. The new (and improved?) switch is only a temperature control. Unless the capillary pressure is low enough, turning it fully CCW will not shut the AC off as the original one did. The blower switch is now the positive off.

All I have left to do now is replace the seats, reattach the capillary coil, and wrap the expansion valve/coils with insulating tape. Whew, I'm almost 80 years old, and this kind of work gets the old bod complaining.

 

I have one last comment regarding the replacement switch. In addition to the capillary tube length and the switch inability to completely shut off the AC, its shaft (where you attach the knob) protrudes too far beyond its threaded collar. There now is a gap under the knob. The length of the threaded section through which the shaft passes is too short to place a spacer that would lower the switch. So now I must use an air driven cut off wheel and shorten the shaft. The part was purchased from Maranello Classic Parts.

 

61931100/A

I think the A stands for aggravation.