AC Diode

[Dr_Snooz]

My AC konked out yesterday. It's charged but the compressor won't run and the fans don't come on. Blower fan works fine. I followed the troubleshooting section of the manual and identified the AC Diode as bad. The dealer doesn't sell these anymore and the parts stores don't even know what a diode is. I might head to the junkyard, but I'm reluctant to get electronic parts from the yard.

Questions:
1. Does anyone know where I can get a new or NOS diode?
2. If I choose to buy standard diodes from the electronics store and wire them in, do I need to know anything special to make it work? eg: are there rough service environment diodes, or diodes for specific applications or anything?
3. Should I just buy a freakin' junkyard diode already and stop the constant worrying about things?

Thank you!

[DBMaster]

I think I know the part of which you speak. Got a pic, perhaps? I am pretty sure an electronics parts store should have what you need if you know the spec(s). I don't know about you, but gotta have air here. It was 106 today.

[lostforawhile]

My AC konked out yesterday. It's charged but the compressor won't run and the fans don't come on. Blower fan works fine. I followed the troubleshooting section of the manual and identified the AC Diode as bad. The dealer doesn't sell these anymore and the parts stores don't even know what a diode is. I might head to the junkyard, but I'm reluctant to get electronic parts from the yard.

Questions:
1. Does anyone know where I can get a new or NOS diode?
2. If I choose to buy standard diodes from the electronics store and wire them in, do I need to know anything special to make it work? eg: are there rough service environment diodes, or diodes for specific applications or anything?
3. Should I just buy a freakin' junkyard diode already and stop the constant worrying about things?

Thank you!

go to the yard,look for Lincoln towncars or crown victorias,on the drivers side there is a little compartment that slides off of the electrical panel,it will say PCM and fuel pump relay and Ac diode, the AC diode unplugs from this and has spade terminals, these are a good high current diode for about any AC system. if you can't find one I'll send you one, all you have to do is splice in spade terminals in your system. Look for a mercury marquie also, around 90-95 for all the years,other full size fords may also have this. The difference between these and electronic store diodes is these are heavy duty ones and sealed against weather

[Dr_Snooz]

go to the yard,look for Lincoln towncars or crown victorias,on the drivers side there is a little compartment that slides off of the electrical panel,it will say PCM and fuel pump relay and Ac diode, the AC diode unplugs from this and has spade terminals, these are a good high current diode for about any AC system. if you can't find one I'll send you one, all you have to do is splice in spade terminals in your system. Look for a mercury marquie also, around 90-95 for all the years,other full size fords may also have this. The difference between these and electronic store diodes is these are heavy duty ones and sealed against weather

Good stuff! Thanks!! The electric panel on the Crown Vics, is that in the engine bay or the cabin? Honda put this diode in about the worst place imaginable for an electronic part. Right next to the radiator and condenser and a few inches away from the exhaust manifold. Like you, I was worried about the electronics store diodes being too wimpy.

[lostforawhile]

Good stuff! Thanks!! The electric panel on the Crown Vics, is that in the engine bay or the cabin? Honda put this diode in about the worst place imaginable for an electronic part. Right next to the radiator and condenser and a few inches away from the exhaust manifold. Like you, I was worried about the electronics store diodes being too wimpy.

drivers side right near the firewall, it will be in a seperate piece that slides into the electrical box, you pull it straight up,then the piece with the relays and diode slides out the end, it will also have ac cutout relay printed on the box, the diode is the smallest piece in there that unplugs and I believe a diode picture stamped into it, if you can't find one let me know I probably have one in my junk

[Dr_Snooz]

After checking three different diodes at the yard and finding them to be bad, I suspected that I wasn't testing them properly. Per the manual, I was testing them by checking ohms across the unit. That showed every diode as being bad. Turns out that there is a diode tester setting on my multimeter. When I use that, I find that my existing diode is still good. That makes no sense to me, but whatever.

Onward through the troubleshooting sequence!

[Oldblueaccord]

yes you need a meter that has a selection for testing diodes.

Hey can you show a pic of where that is or maybe the relay I couldn't find either. I have a new relay. I think its on the inner fender near the drier.


wp

[Dr_Snooz]

I don't have a picture, unfortunately. There is one in the ETM, but it's pretty much useless. The Diode and the clutch relay are hung on the same bolt, between the radiator and the headlight bucket, in front of the PS pump, on the driver's side. If you remove the piece of sheet metal that goes over top of the radiator, the relay will be slightly less difficult to access. It's a cylindrically shaped relay.

According to the troubleshooting procedure on p. 23-8, my diode is bad. Yet according to the diode test on p. 23-42, the diode is good. As far as I can tell by looking at the system schematic on p. 23-4, the troubleshooting procedure is wrong. In it, you're supposed to be shorting past the diode, but all you're doing is grounding a ground to itself. That's what it looks like, but I'm reluctant to go against Soichiro's engineers.

If I short across the pressure switch, the system comes on. The system has a 150 psi static charge in it, so that means the pressure switch is bad, right? It's a $35 part, so I kinda want to be sure.

Thanks again everyone.

[obd0driver]

Ill sale you my ac stuff for dirt cheap ($35) for the pump. If that help's ill be at the cam meet Saturday if you can make(i know its far) or ill ship it to you u pay the shipping.

[nswst8]

My problem was the thermostat switch at the evaporator the wire on the outside of the evap box is the switch terminal connection. Interior of the car.

[lostforawhile]

I don't have a picture, unfortunately. There is one in the ETM, but it's pretty much useless. The Diode and the clutch relay are hung on the same bolt, between the radiator and the headlight bucket, in front of the PS pump, on the driver's side. If you remove the piece of sheet metal that goes over top of the radiator, the relay will be slightly less difficult to access. It's a cylindrically shaped relay.

According to the troubleshooting procedure on p. 23-8, my diode is bad. Yet according to the diode test on p. 23-42, the diode is good. As far as I can tell by looking at the system schematic on p. 23-4, the troubleshooting procedure is wrong. In it, you're supposed to be shorting past the diode, but all you're doing is grounding a ground to itself. That's what it looks like, but I'm reluctant to go against Soichiro's engineers.

If I short across the pressure switch, the system comes on. The system has a 150 psi static charge in it, so that means the pressure switch is bad, right? It's a $35 part, so I kinda want to be sure.

Thanks again everyone.

if the system has pressure like it's supposed to, and the pressure switch is still open, the switch is bad, have you checked the system with it running and seen if it 's getting cold? have you looked for a used switch at the yard?

[lostforawhile]

After checking three different diodes at the yard and finding them to be bad, I suspected that I wasn't testing them properly. Per the manual, I was testing them by checking ohms across the unit. That showed every diode as being bad. Turns out that there is a diode tester setting on my multimeter. When I use that, I find that my existing diode is still good. That makes no sense to me, but whatever.

Onward through the troubleshooting sequence!

A diode isn't like a resistor or other component, it requires a small amount of voltage to overcome the junction in the diode, this is what causes the voltage drop across the diode also, on the resistance setting there isn't any voltage to overcome the junction, when you set the meter to diode test there will be a small amount of voltage between the probes, l

[Oldblueaccord]

yes you need a meter that has a selection for testing diodes.

Hey can you show a pic of where that is or maybe the relay I couldn't find either. I have a new relay. I think its on the inner fender near the drier.


wp

http://ocw.weber.edu/automotive-tech...t-measurements

I think its a shunt for the clutch but im not sure if its bad if the clutch would not work or not. I don't see why you could not jump it out for a test.


wp

[POS carb]

does the "A/C" lamp illuminate on the dash?
have you tried to jump the pressure switch by the drier?
when you click on different vent settings (floor, defrost, vent) does it work?

[Dr_Snooz]

Jumping the switch makes it run. The light is on. Not sure about the vents, but I think they work fine. I got the part a few days ago, just need to put it in.

[POS carb]

me thinks pressure switch