No A/C

Your compressor will not engage if the system pressure is too low. Connect a set of gages on the low and high side and read the system pressure.

Milton

 

The only things that can cause the relay itself to thermally overheat are:

1. a defect in the relay contacts (but you've already tried a new one)

2. the AC system is drawing more current than intended (but this should blow the fuse before hurting a 30A relay), or

3. even when things are working as intended, the current flowing thru the AC relay is big -- probably more than 10A. If the electrical connection from the 30 or 87 relay tab -to- relay socket -to- trace on PWB has any resistance at all (even just a few tenths of an Ohm) the I^2*R heating will be significant and either toast the relay, the relay socket piece, or PCB trace/pad -- I'd look there first for signs of overheating/damage.

Can you confirm that when the system stops working that the fan blower motor also stops working? (I believe the blower fans should always work regardless of what going on with the compressor, high/low switches, refrigerant.)

 

Well, maybe a simplier explanation is that it's the same effect that causes the "burning" at the white connector pins that carry big currents -- things get damaged from the overheating (so just like you're inspecting the white connectors for "burning" also check the relay socket and the corresponding PCB pad/traces for visual signs of "burning").

My question was about the fans that blow air into the cabin (not the condensor fan) -- do the interior fans work, or not work, when you have the problem?

 

The interior fan is a quasi-separate system (from the compressor, refrigerant, and high/low switches) so it not working might indicates that you are losing the common +12V power to run the whole AC system.

The first place to measure/look is at pin #8 on the W connector:

If the w connector pin 8 is at +12V when the problem is happening -- the trouble is probably in the relay/electrics on the AC unit itself.

If the w connector pin 8 is at 0V when the problem is happening -- the trouble is somewhere in the +12V food chain from "battery -to- connector A -to- PCB trace -to- fuse #18 -to- PCB trace -to- relay s (which gets closed by relay v when the key is "on") -to- PCB trace -to- male pin at connector W -to- female socket of connector W -to- crimped MN (brown/black) wires".

If you can determine which case is occurring, this will show where to go next.
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The first thing to do would be to unplug the w connector and check the conditions of the female pin in the connector, the male pin on the PBCA, and the PCBA itself for signs of thermal damage. If that all seems OK, plug the w connector back in, and partially "unplug" relay s so that the male tabs on relay s are still making electrical contact with their corresponding female sockets, but you have enough access to get the voltmeter probe (or a wire) on the male tabs of relay s -- if things are "working" as intended, you should get the following results (the tab numbers are physically shown on the bottom of the relay if you aren't familiar with that yet):

ignition key "off"
tab 30 is always at +12V relative to ground (although sometimes they get terminals 30 and 87 switched in the labeling on the schematic so if terminal 30 is not at +12V check terminal 87 too).

ignition key "on"
tab 30 is still at +12V relative to ground
tab 87 is at +12V relative to ground
the voltage between tabs 85 and 86 is +12V (or -12V depending on which probe of your voltmeter is on which tab)

Report back which conditions are met, or not met, and we'll go from there.

 

I probably should have asked you to unplug the w connector for that key "off" measurement -- you might try that to determine which terminal is really the +12V supply to the relay. If they are still both +12V with the key "off" with the w connector unplugged, also unplug the relay s completely and make the voltage measurement to the female terminals in the relay socket. If they are both still +12V, I think that would indicate a short inside the PCB.

However, having both #30 and #87 show no voltage under load is an indication that you have a high-resistance "break" somewhere in the chain from:

battery "+" terminal
connector a
upper fuse terminal
lower fuse terminal
terminal 30 at relay s (which you've already verified is dead under load)

With the key "on" and the AC button pressed - try measuring at those locations to see the last place that you do have the +12V present.

 

Nathan -- I'm not getting a clear message about your problem. Certainly, the AC pin at the w connector being badly burned is bad (and needs to be corrected -- I asked you to check this in post #13!), but, if that's the real problem, you should still measure the +12V (relative to ground) at terminals #30 and #87 of relay s with the key "on" (i.e., with relays s and v "closed" -- whether the AC button is pressed or not) so I don't understand that.

"PCB" is the abbreviation for printed circuit board, but this often gets called the fuse panel, or the relay panel, or the fuse box, or PWB (printed wiring board), etc. -- based on the prior posts, Mondials have particularly troublesome ones

Bottom line is that you need an electrical connection (capable of carrying a large current) going from the 87 terminal of relay s over to the brown/black wires leaving the w connector to run the AC system. If you do a search on "tr white connectors", you should get some prior threads with similar discussion about various possible ways to fix this problem.

 

No need to remove the PCB yet (but you may get there)-- unless it's obvious that the male pin or PCB is badly damaged beyond use (and the actual copper connecting trace could be visible on the outside surface or it could be "buried" inside the multilayer PCB). With key "off", unplug relay s and the w connector, and measure the DC resistance from the 87 terminal of the relay s socket to the male pin on the PCB that mates with the brown/black wires in connector w -- should be low (just a few Ohms maximum).

If that's OK, and if the male pin (and the corresponding copper trace and solder area) on the PCB is/are still in good shape, you can clean up the surfaces on the male pin (where the female pin contacts it) and either replace, or restore, the female pin too. Otherwise, most everything I know on the subject is already in those "tr white connector" threads (but feel free to give a shout if needed).

There are surprisingly few wires at the AC control on the F of your era. Basically, when you turn the key "on", every AC component gets +12V made available by relay s (if everything's OK -- like that w connector pin). When you press an AC control button, this connects the single "ground" to turn it all "on" (and the vacuum lines control actuators that move the various flaps around to direct the airflow). If/when you can confirm that the brown/black wires at the w connector are at +12V, but the AC system/blower still doesn't work, that would be the time to consider the AC pushbutton is not making the proper ground connection.

 

You'll need to go in from the front side (IIRC) with a narrow pick or screwdriver and hold/bend the locking tab piece of the terminal "in" as you withdraw the wire and terminal out towards the wire side. Before reinserting, bend the lock tab back out so that it clicks into place after reinsertion.

Does anyone have a close-up pic of that 2-prong female terminal that they could post?

 

Not really, but I'd start with RicambiAmerica, FerrariUK, TRutlands, etc....

(I have a vague recollection of someone mentioning a source for the individual female pins -- but I can't find that thread.)

 

Shark,
is the AC related problem solved now?