I'm new to this forum and this is my first post. Because of my paranoia, I'm in the habit of turning on my A/C when the temp starts to creep up above 225. Now my A/C will not cool and neither of the cooling fans runs with A/C on. The blower fans run though. I've checked all fuses both those in engine compartment and pass side box and they are all good. I have no OBD II codes nor any DTC codes. Can anyone give me a hint on possible problems or where to start looking? I apologize in advande if this topic has been beaten to death. Thx.

 

Oops, sorry I forgot to mention that this is a 96 LT4

 

If the compressor clutch isn't engaging but there isn't a low gas code (flashing LED on the Controls), might just be an intermittent connection at the Low Pressure Switch. Unplug it and plug it back in - wriggle it around - hold the connector firmly onto the switch. If at all works again, the connector or the switch or both are bad. If that doesn't do it, clear system memory by disconnecting and reconnecting the battery. If it runs and goes out again, I'd guess it's sensing a problem such as a low charge.

 

My prob turned out to be frayed wires going into the clutch. they where right where they enter it and covered with dirt so I couldn't see them . fixed them with heat shrink tube. Just another thing to check.

 

Thanks SunCR for your prompt reply!
I did the plug/unplug, jiggle test with negative results. Same with resetting the memory with battery reset. nada. Any other thoughts?

 

Hook up a jumper lead across the plug to the low pressure switch to complete the circuit and see what happens. Let us all know.

 

Are you sure you are not low on freon, gauge readings would help. Mine didn't show codes either and was low on freon.

 

If the cooling primary fan is not starting as also the compressor, it sounds like the PCM or HVAC programmer is not getting an A/C start signal from the onset. Low freon will cause no cooling, but there is a wide range between low freon, and before the low freon error code will be set. I would forget about the freon at this point. I think once you get the fan running, the A/C will work OK. You might try cleaning the connector and plug of the HVAC programmer for starters. Does the fan start in any other A/C mode? You can try lightly tapping or push the programmer and try again before disassembly.

Of course checking for anything loose, not seated correctly or bad connection is a possibility.

On a 94 and up. Only one fan will start with A/C on. (It should run also when 225* is reached controled by PCM). Secondary fan will not come on until 239* and the PCM controls this by checking temp sensor at water pump.

I think first things first, got to get that fan runing and I think the rest will fall in by itself.

No books here, best I can do from memory for now.

 

.....at least for now. My freon level was indeed low even though no DTC 09 code was thrown. So i'm back in business.

Thanks to all for your suggestions. I continue to be amazed at the comraderie and sense of community of this forum. Again thanks, and rock on!

Stan Schneider
"Spy Vet"

 

That’s great, can’t argue with success. I have had low freon a few times and no cooling but never had a fan problem. Wish I understood your chain of events and symptoms better. I was under the impression the compressor did not start. Perhaps your 96 does not operate like my 94, but would sure like to know the answer. Charge on.

 

Cool, as an AC tech I always check the charge. Also because I don't know too much about the electrical system in these cars. That's when I start asking questions.

 

Interesting there was no code. PCM monitors the Low Pressure switch for rapid cycling and the Pressure Sensor voltage to determine if there's a low (or high) charge. Normal operating range of the Pressure Sensor
- mounted on the high pressure line - is somewhere between .8 to 4 volts or about 80 to 400 psi. The PCM also looks for a voltage or pressure rise whenever the clutch engages, so if the Sensor sends an initial voltage signal of .5 volts (50 psi which is threshold that closes the low pressure switch contacts) and it rises to .8 or higher, it senses everything is ok.

I don't know what the actual on/off or cycling sequence the PCM is looking for - never been able to find a published spec. Most Manuals show a diagnostic spec of 8 cycles or less at 70 degrees, but I don't know if this is programmed into the PCM.

Pressure Sensor is also used for fan control when the a/c is on ('90 and above). The threshold for fan operation varies by Year with the '90 -'93 tripping both fans (I think) somewhere around 200 psi. The last '94 specs I saw (from Alldata), was both fans at 150 psi (which makes sense because it's an R134 charge). After that - either '95 or '96 - the 2nd fan not only comes on, but there is a bump in speed if a certain threshold or pressure is reached - I don't have the specs. In any event, the fans aren't going to run if the pressure doesn't reach the threshold for the PCM to ground the relays and that isn't going to happen if the charge is too low - or the outside air temp (usually 50 and below) keeps the pressure below the threshold. I'd guess in this case that the charge was too low - I don't have a good guess as to why there wasn't a code, but I'm thinking: 1. If the clutch was engaging - the PCM was sensing a cold condition - some cycling - a pressure rise signal from the Sensor, but not high enough for the PCM to ground the fan relays; 2. If the clutch wasn't engaging - whatever was in it leaked out so fast the low pressure switch contacts never closed, so there wasn't anything to monitor.

Do hope you had it leaked check - particulary if the latter scenario is the reason there wasn't a code. I spent some time in Annapolis and no a/c in the summer isn't much fun there (isn't much fun out here this Year either).