[Bearhawke]

Here's I hoping it's just a defective O ring although thank God for R134..................

 

[KOG]

Or HC 12 which works noticeably better for me than 134 ever did. The main leak problem I've had with that model has been dryer gaskets which are a PITA. Oh, and the oddball schraeder valves.

 

[Bearhawke]

Or HC 12 which works noticeably better for me than 134 ever did. The main leak problem I've had with that model has been dryer gaskets which are a PITA. Oh, and the oddball schraeder valves.

I believe my van was R134 from Chrysler; 1993 was the transition year.

 

[KOG]

Yep, 93 was 134. And I've now got HC12 in the 93 and the 94 as well as the 91 and 92, both of which have been upgraded to 93/94 condensers, radiators, fans and compressors.

 

[Bearhawke]

At work we checked the R134 level; according to the gauges; everything's OK. Though the engine cooling fan doesn't come and stay on (cycles on and off) when the AC is swtiched on; is that normal? Alldata is skimpy at best on info..............

 

[KOG]

Something not right there. The cooling fan should be on when the A/C is running IF you're getting much cooling. Fan is controlled by a pressure switch on the high side. back through the SMEC. Get some gauges on it and find out what it's doing.

 

[Bearhawke]

Something not right there. The cooling fan should be on when the A/C is running IF you're getting much cooling. Fan is controlled by a pressure switch on the high side. back through the SMEC. Get some gauges on it and find out what it's doing.

'SMEC'? As you can probably tell; underhood isn't my strong suit. If I understand what you're saying, I may have a computer problem?

Low side about 30, high side (fan off) 300 or was the 200, (fan on) 175 and dropping. What bugs our master tech is why the rad fan cycles on and off instead of running continuously----------unless it's indeed the engine computer. I even swapped around several relays in the fuse panel (same numbers), no difference.

 

[KOG]

SMEC = single module engine controller, Chrysler speak for engine computer. The 175 lb reading with fan on is low enough to turn the fan off. If low side is holding at 30 it should be getting COLD. Cycling of fan is probably normal under those conditions.

 

[John Wood]

Any chance this is a variable displacement compressor? Check the valve at the firewall. If it is black you have a variable displacement compressor and they run all the time when the AC panel switch is on. If the valve at the firewall is silver (that is the expansion valve), you have the conventional system that cycles on and off via an evaporator probe signal.

 

[Bearhawke]

Any chance this is a variable displacement compressor? Check the valve at the firewall. If it is black you have a variable displacement compressor and they run all the time when the AC panel switch is on. If the valve at the firewall is silver (that is the expansion valve), you have the conventional system that cycles on and off via an evaporator probe signal.

That valve on the firewall (the one that's about 2" x 2" x 3.5") is silver in color. The Ac does work somewhat but def not cold enough..............

Note the compressor runs all the time but the rad fan cycles on and off. Is it possible my fan is defective and is cutting in and out due to its elector motor overheating?

 

[John Wood]

That valve on the firewall (the one that's about 2" x 2" x 3.5") is silver in color. The Ac does work somewhat but def not cold enough..............

Note the compressor runs all the time but the rad fan cycles on and off. Is it possible my fan is defective and is cutting in and out due to its elector motor overheating?

Even if the fan motor was cutting out on a thermal breaker (which I don't think it has), the radiator fan relay would still stay closed which prevents the clutch relay from opening.

Check the temperature of the pipes going into the the expansion valve. If one of those is pretty cold (suction line) before it cuts out and you are getting some moisture on the pipe (maybe not in dry Arizona), that is a pretty good indication that your refrigeration system is functioning. Actually, 30 PSI on the suction line and 250+ on the high side is not bad and should indicate a good system. Are you sure the compressor front is turning all the time? This is sure a strange situation. It should definitely disengage when the fan stops. What is the high pressure doing when the fan stops? . If the compressor still running, the high side should rise rapidly.

 

[Bearhawke]

Even if the fan motor was cutting out on a thermal breaker (which I don't think it has), the radiator fan relay would still stay closed which prevents the clutch relay from opening.

Check the temperature of the pipes going into the the expansion valve. If one of those is pretty cold (suction line) before it cuts out and you are getting some moisture on the pipe (maybe not in dry Arizona), that is a pretty good indication that your refrigeration system is functioning. Actually, 30 PSI on the suction line and 250+ on the high side is not bad and should indicate a good system. Are you sure the compressor front is turning all the time? This is sure a strange situation. It should definitely disengage when the fan stops. What is the high pressure doing when the fan stops? . If the compressor still running, the high side should rise rapidly.

The thinner AC line gets very hot, not cold. Compressor runs all the time. When the rad fan is running; the AC high side pressure drops down to under 200 then jumps back up with that fan back off. Note too since this is our 'humid' season, the AC should be 'sweating'.

As I mentioned earlier in this thread; the techs here at work are perplexed as well.

 

[John Wood]

As I mentioned earlier in this thread; the techs here at work are perplexed as well.

I can see why.

There is a logic malfunction. The computer is calling for the fans to cutoff when they shouldn't be and it is keeping the AC clurch relay closed (or it appears that way). Can you pull the AC clutch relay and cause the AC clutch open (and stop the compressor)?

Could the clutch relay contacts be stuck in the closed position? (but you swapped several relays, right?)

 

[Bearhawke]

I can see why.

There is a logic malfunction. The computer is calling for the fans to cutoff when they shouldn't be and it is keeping the AC clurch relay closed (or it appears that way). Can you pull the AC clutch relay and cause the AC clutch open (and stop the compressor)?

Could the clutch relay contacts be stuck in the closed position? (but you swapped several relays, right?)

Unplugged the AC clutch relay, compressor shut off, swapped that relay with another and still the same thing (compressor running all the time and the rad fan switching on and off). I'm starting to suspect the computer is dying especially in light of it tripping the Check Engine light once in a great while and after a long high speed freeway run esepcially one a hot day (note the engine temp gauge is around half way up, normally, the needle points towards the lower side of the scale), when I come to a stop, the motor wants to stall...........almost like a vapor locking carburetor.

 

[John Wood]

Unplugged the AC clutch relay, compressor shut off, swapped that relay with another and still the same thing (compressor running all the time and the rad fan switching on and off). I'm starting to suspect the computer is dying especially in light of it tripping the Check Engine light once in a great while and after a long high speed freeway run esepcially one a hot day (note the engine temp gauge is around half way up, normally, the needle points towards the lower side of the scale), when I come to a stop, the motor wants to stall...........almost like a vapor locking carburetor.

I'm leaning toward the computer too. I am curious about something and if you wouldn't mind performing another test...

With the vehicle running, AC on, ... try pulling out the fan relay. We know the fan will stop, but I'm curious to know if the AC compressor kicks out.

 

[Bearhawke]

I'm leaning toward the computer too. I am curious about something and if you wouldn't mind performing another test...

With the vehicle running, AC on, ... try pulling out the fan relay. We know the fan will stop, but I'm curious to know if the AC compressor kicks out.

I pulled all three fan relays (rad hi, rad low and rad hi ground) and the AC compressor is still on. :scared:

 

[John Wood]

I pulled all three fan relays (rad hi, rad low and rad hi ground) and the AC compressor is still on. :scared:

...and I suspect the compressor stays on even with the AC and defrost turned off, right?

The computer appears to be applying a solid ground to the clutch relay coil. Normally that is a switched ground and is only turned on when your AC or defrost is selected, pressures are good in the system, cycling switch calls for cooling, high pressure switch is not in cutoff, and the computer gets confirmation that the radiator fan relay is closed. All of those conditions must exist in the logic tree for the computer to close the clutch relay.

My conclusion is that the computer is bad. The only other (very unlikely) possibility is that the clutch relay coil return line (ground) is shorted to ground in the power distribution center or associated wiring back to the computer.

Start shopping for a used 94 computer that matches yours identically (i.e. engine & transmission, US emissions, etc. - part #'s should match if legible).

 

[Bearhawke]

...and I suspect the compressor stays on even with the AC and defrost turned off, right?

The computer appears to be applying a solid ground to the clutch relay coil. Normally that is a switched ground and is only turned on when your AC or defrost is selected, pressures are good in the system, cycling switch calls for cooling, high pressure switch is not in cutoff, and the computer gets confirmation that the radiator fan relay is closed. All of those conditions must exist in the logic tree for the computer to close the clutch relay.

My conclusion is that the computer is bad. The only other (very unlikely) possibility is that the clutch relay coil return line (ground) is shorted to ground in the power distribution center or associated wiring back to the computer.

Start shopping for a used 94 computer that matches yours identically (i.e. engine & transmission, US emissions, etc. - part #'s should match if legible).

When the AC switch is off, the compressor is off.

 

[John Wood]

When the AC switch is off, the compressor is off.

OK, that eliminates a 'hard' ground fault like the wiring between the computer and the PDC or the PDC shorting the relay coil to ground.

I'm still suspecting the computer but have you tried pulling the low pressure plug on the expansion valve (silver valve discussed earlier) to see if the compressor kicks off?

 

[Oklahoma Wolf]

Fan is controlled by a pressure switch on the high side. back through the SMEC.

The fans cycling like they are makes me wonder about this switch. May be faulty. I'd put a jumper wire on the connector to make the fans run full time and see if the system starts cooling better then.

The Imperial had a similar issue when I converted to HC-12A, and it's all because of that switch. Switch didn't see R12 high side pressures, fans didn't come on often enough, and the system would only blow cold on the highway. Mine is a variable displacement compressor, so it does run all the time, but the fan pressure switch operation should be similar. I ended up installing a relay to make the fans run whenever the compressor was running. We had 95 degree weather the other day, and the system was just fine with that.