2000 Caravan A/C and Cooling Fan Problem

pav9768 · #1 06-03-2007, 04:29 PM

Hoping that someone can help. 2000 grand caravan 3.3L A/C is not working. When I turn on the A/C the rad cooling fans do not come on and it is my understanding that they should. The fans will come on for high temp but not for A/C on. The A/C Clutch engages when I turn the A/C on and I checked the A/C switch signal coming from the A/C Heater Control Module it seems ok (13.2v with a/c off) and goes to ground when I turn on the A/C. Seems that the PCM is seeing the A/C on signal because it is picking-up the A/C clutch. I can not understand why the cooling fan relay isn't picking-up or being pulsed. From the info I can gather the PCM only has one output to the Cooling Fan Relay but has two inputs (high temp and A/C On) that will produce this output. Looking at all the checks I made I fear that I have a bad PCM. If anyone has any suggestions I will appreciate any help. Thanks in advance

RIP · #2 06-04-2007, 01:13 PM

The fan control module (rad fan relay) is looking for a ground from the PCM to turn the fans on. If the PCM doesn't provide the ground - no fans. On 1998s, contact #73 is the contact for the ground out of the PCM. Not sure if it's the same on yours. If you can confirm which contact is the ground, disconnect the PCM and short it to ground (not on the PCM, but on the wire harness connector). If the fans come on that tells you that wire from the PCM to the fan control module is good and the system should work if the PCM cooperates. If that's the case I would start looking for a new PCM. If they still don't come on inspect the wiring to the relay.

Try cleaning the PCM connections.

Spit · #3 06-04-2007, 03:13 PM

My 1997 Grand Caravan works the same. The fans do not come on until the coolant is reading hot. Is this for sure not correct?

Spit

pav9768 · #4 06-04-2007, 04:09 PM

RIP, Thanks for your reply. I was under the impression that the PCM gave the fan relay a varying + DC Pulse and looking at the schematic it shows 4 inputs to the solid state fan relay. Inputs are BATTERY- which goes to a 40A fuse, FAN OUT- goes to one side of the fans (other side of fans are grounded and both are in parallel) GROUND- goes to ground, and RELAY CONTROL IN- which goes to the PCM. I have nothing but an owners manual and a Haynes Repair Manual to go by. I haven't physically looked at the fan relay to see if it is wired the way the Haynes Book says it is I assumed that since the fans worked on high temp that the relay and wiring to the PCM was ok. I will have to look and see how the relay is wired. Also... I cleaned the PCM contacts and the A/C Heater Control Contacts both pin and plug sides. Nothing looked discolored or burnt. Thanks again.

SPIT, I believe that the fans should come on when you turn the Air Conditioning on

Stretch58 · #5 06-04-2007, 06:50 PM

The fan operates based on temperature and A/C pressure.
On at 220deg F 30% speed, 230 Deg speed ramps up to 100%. Fan ramps back down from 100% to 31% and shuts off at 214Deg.

When AC is on, 30% speed at 250psi, ramps up with pressure to 99%, 300 PSI
ramps back down with pressure and turns off at 248 psi.

Its what my book says.

Possible low A/C pressure?

pav9768 · #6 06-04-2007, 07:00 PM

Stretch58, Thanks for that info. Gives me something to check. I didn't check the pressure switch/transducer because I didn't see it in the fan circuit.

Spit · #7 06-05-2007, 05:34 PM

I got the same information that Stretch58 shared with us, today from a Dodge Dealer. Does anyone know where the pressure transducer on the high side is located? I have never really checked the fans that carefully on my van. I do know that they kick in and that the temp gauge never reads above half way. Since I have had problems with my AC and may not have enough pressure on the high side to make the fans kick on...Maybe I am operating strictly on coolant temp. which seems to be keeping the engine in a safe range but maybe not a cool as it should be.

Chuck

Stretch58 · #8 06-05-2007, 08:33 PM

Quote:

Originally Posted by Spit

I got the same information that Stretch58 shared with us, today from a Dodge Dealer. Does anyone know where the pressure transducer on the high side is located? I have never really checked the fans that carefully on my van. I do know that they kick in and that the temp gauge never reads above half way. Since I have had problems with my AC and may not have enough pressure on the high side to make the fans kick on...Maybe I am operating strictly on coolant temp. which seems to be keeping the engine in a safe range but maybe not a cool as it should be.

Chuck

Chuck
As you face the engine compartment from in front of the radiator, the transducer is just to the left of the alternator pully on a line almost on the firewall. Normal voltage range from sensor when A/C is operating is .451 to 4.519 VDC.

RIP · #9 06-05-2007, 10:48 PM

Quote:

Originally Posted by pav9768

RIP, Thanks for your reply. I was under the impression that the PCM gave the fan relay a varying + DC Pulse and looking at the schematic it shows 4 inputs to the solid state fan relay. Inputs are BATTERY- which goes to a 40A fuse, FAN OUT- goes to one side of the fans (other side of fans are grounded and both are in parallel) GROUND- goes to ground, and RELAY CONTROL IN- which goes to the PCM. I have nothing but an owners manual and a Haynes Repair Manual to go by. I haven't physically looked at the fan relay to see if it is wired the way the Haynes Book says it is I assumed that since the fans worked on high temp that the relay and wiring to the PCM was ok. I will have to look and see how the relay is wired. Also... I cleaned the PCM contacts and the A/C Heater Control Contacts both pin and plug sides. Nothing looked discolored or burnt. Thanks again.

pav9768 - I was going strictly by what the Haynes manual schematic presented. The narrative on how the system works is sadly lacking. Nothing about a pulse. Now that you mentioned it I recall seeing reference to a pulse in other posts. Thanks for the reminder. Looks like Stretch58 has a much more detailed book to go by. Good source of info. Hope you nail it soon.

Spit · #10 06-06-2007, 07:54 AM

Thanks Stretch..I found it last night. I assumed it was a high or low pressure cut-off switch.... So let me ask you a couple of questions.

How would I check the voltage? back probe the wires?

I assume that there are terminals on the transducer itself, If I remove the wires and do a check on those terminals should I read any voltage or continuity or open?

Does the transducer generate it's own current? or just open & close like a normal switch?

From memory..refering to a chart of operating pressure from my Haynes AC manual It seems like the normal high side range on a Grand Caravan wouldn't always be at the 248 or 250 that it seems to kick on fans on?

pav9768 · #11 06-06-2007, 11:25 AM

RIP, STRETCH58 and all others. Thanks for the help. I will look at my A/C pressures and the pressure switch circuit this weekend... hopefully it's just a slow leak and I can give it a boost. I will post my results.

Stretch58 · #12 06-06-2007, 11:34 AM

Quote:

Originally Posted by Spit

Thanks Stretch..I found it last night. I assumed it was a high or low pressure cut-off switch.... So let me ask you a couple of questions.

How would I check the voltage? back probe the wires?

I assume that there are terminals on the transducer itself, If I remove the wires and do a check on those terminals should I read any voltage or continuity or open?

Does the transducer generate it's own current? or just open & close like a normal switch?

From memory..refering to a chart of operating pressure from my Haynes AC manual It seems like the normal high side range on a Grand Caravan wouldn't always be at the 248 or 250 that it seems to kick on fans on?

As I recall the transducer has a 5VDC supply and ground, it also has a takeoff for the variable signal on another wire. In the book they do not say how to check that with a meter only. Just at the dealer, with his scan tool set to monitor that input. To read the voltage with a vom, you would have to follow the wires till you get to a safe, accessable spot and probe thru the insulation. Might not hurt to have someone check out the A/C on that unit for pressures etc. You can't read the output of the transducer disconnected, since I think that would turn off the A/C.

pav9768 · #13 06-07-2007, 04:07 PM

Ok I couldn't wait until the weekend I had to know. I put gauges on the low and high sides,started the van and turned on the A/C. When I turned on the A/C the compressor clutch engaged but no fans. Low side pressure was 25psi and the high side started at around 200psi. I let the compressor run and I noticed the high side pressure starting to creep up slowly. After a few minutes the high side pressure got up to 250psi and the fans turned on. As soon as the fans turned on the high side pressure started to drop and the low side started to rise the fans continued to run (maybe because of high temp) not sure but when it was all said and done both the high side and low side pressures equalled out at 100psi. Hoping someone can make sence of this. As always any help would be appreciated

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