1988 Mondial 3.2 Cab So my ac was acting up, seemed to cool and then cut out, most noticeable while at a stop light or idling in traffic. Inspected various things for any obvious leaks, nothing obvious, did a low pressure line test using a crappy old gauge, it was about 35 psi at 78 degrees f, so looked like the (r134) charge was fine. Still the same problem, cooled fine on some occasions then cutting out. Put on proper ac gauges, at 78 degrees, system off pressure was about 75psi, and system on, my low side was about 35psi, but the high side seemed high was at about 250psi and crept up to 350psi, then the unit cut out. My instincts had me look at the condenser, appears the fan was not going on. Wiggled the connections, swapped the relay, checked the fuse, still not fan going on. Fan spins by hand, no sign of seized bearings. So my questions are: Is the fan supposed to go on right away when the a/c compressor kicks in, and stay on most of the time when the car is idling in traffic and such? Not sure when it has historically gone on and off. There is one wire on top of the motor, and one on the bottom which goes to the temperature sensor on the nearby line. How can I test diagnose the motor to see if it is still good? Verses determine if the temp sensor is the problem or something else in the wiring/ac switch etc.?
Just unplug the thermoswitch ("the temperature sensor on the nearby line"), and use a jumper wire to connect the two terminals in the connector of the wiring harness (simulating a "hot"/closed thermoswitch) -- then the AC condensor fan motor should come "on" as soon as the AC system is switched "on": If it does = bad thermoswitch If it doesn't = measure the voltage between the two wires going to the motor: If +12V (but motor doesn't run) = bad motor (probably something in the commutator/brushes/brush springs - which get wet too often ) If not +12V = some upstream electrical trouble (e.g. - white connector foo) Good Hunting!
It is probably the thermoswitch, mine was doing the same thing - not cooling when stopped or moving slowly in traffic. When I bypassed the switch, the fan worked fine and cooling was restored to normal. You can unplug the wire from the switch and plug it directly into the fan, very easy to do and the connector is a match. I replaced the bi-metal switch and all is good now. Bypassing the switch permanently so the fan was on any time the AC was on seemed like an OK solution too. Just in case you don't know - the switch is clamped to the one of the coolant lines just before the condensor fan, with a single wire running to the fan from the switch. Alden
Thank you for the tips fellows, the fan is good, the switch is not. Bypassed, for the hot summer city driving makes sense while I await a new switch. But before I confirm the old one is dead, it showed no continuity at room temp, when I dipped it into boiling water it showed about 0.600M ohm resistance? What would be normal resistance on an open circuit in this switch? Maybe I just need to really clean up the contacts (which look fine after a superficial cleaning)?
0.6 Meg-Ohms is far too much resistance for the "on"/closed/hot condition -- a properly working thermoswitch would just be a couple~few Ohms resistance maximum when closed/hot.
Thanks for clarifying, time for a new switch. fyi, for anyone else who looks at this thread in the future, the sensor has 42 degrees / 37 degrees stamped on the side, presumably the actuation temperature in centigrade, with what might be a part number 9051801 on it.
So I did various other tests on the old switch (dipped in boiling water, measured with meter and this time not having measured the resistance of my fingers , etc.), and confirmed for sure it is not working properly. Switch closed but at way too high a temp, and still had too much resistance when open). Tried to source a replacement, all the usual sources, no one carries it, even at list prices from $200 to $400. Part number 61047900. Also for qv's, 328, some Testarossas and the 288GTO. Checked less popular sources, looks to be NLA. Tried to find a cross to Mercedes or other cars of the period, no luck. Thought of finding a used one, but there is a cycle life span for this switch and it is on and off frequently, and not sure any available in any event. I managed to find a similar sensor by a US company, not quite the same robust clip attachment as OEM but should be fine. The item that is the correct fit is this one... http://senasys.com/product/2570f110-thermal-switch You need the half inch pipe size, the actual pipe is metric and would be about 7/16", so the smaller 3/8 inch one would not get the correct surface area contact of the pipe, and the company advised to upsize to the best fit. I also purchased their thermal paste to ensure the sensor reads as accurately as possible. The OEM close open temperature is 42C and 37C, which is about 108F and 99F, so the closest Senasys one is F-021, which is 110F 95F with +-5F so looks to be the correct equivalent to the OEM. You need to crimp on the typical 1/4inch spade connectors, reuse the plastic connector covers on the old item, and the ac fan now cycles on and off as it should. All for about $15. They do have a different smaller unit that would probably look even closer like the OEM unit (wires out of the side on mine, the other smaller one has wires out the back like OEM), and would presumably clip on more like the OEM style clip unit, but it does not come with the correct temperature range. I suppose the company would outright custom make something as close as possible to the OEM unit if there was interest (I will leave that to an enterprising 288GTO owner seeking concours perfection!), but the off the shelf unit seems functional, although as I mentioned the side mounted clip is a bit loose for my liking, the OEM one was really clipped on tight. To be clear, you can bypass the switch entirely and just connect a plain wire to the fan bottom connector and the wire loom connector, the fan will be on all the time when the ac is turned on. With my city driving, the fan is on almost always anyways, so for those in a hot climate this thermo switch may be redundant. But for the cost of the Senasys one, may as well have the original OEM intended function, and presumably optimizing the ac temperatures while minimizing the long term wear on the condensor fan motor. So that ends my fan switch saga, with a happy ending. I am really glad companies like Senasys exist and will deal with small quantity orders with prompt shipping and such.
