Not Your Average A/C Problem - Check This Out

[Brook24v]

'94 MTX - Around 280,000 miles. Fully charged A/C system.

This car will lose it's fresh cold air after about 20 minutes of driving, while other times it will work for over an hour. It's really weird. When it works it is cold as ice, but out of nowhere you will smell/feel the humid air as if the A/C just shut off. It sucks.

Now obviously one would blame this on the blend door, so I unplugged it while she was blowing cold and about 20 minutes later I got that musty smell as the air turned warm. Looks like that rules out a possible bad blend door. So what else would control the A/C from kicking on/off? Some kind of relay? Would something get too much voltage causing the system to shut down? Someone throw me a bone here! Thanks!

:thankyou:

 

[SHOtimer]

The clutch on your AC compressor needs to have a shim removed.

Doug

 

[sholover719]

it could also be possible that one of the pressure sensors that controls when the a.c compressor kicks on and off with either to much pressure or to little pressure in the lines.

 

[86si]

Corroded ground

 

[projectSHO89]

Probably none of the above.

Your symptoms are consistent with evaporator icing. Telltales include a LARGE puddle of water under the evaporator outlet after the car is parked or frost on the evporator to accumulator line.

Typical faults include a cycling switch stuck closed, an AC clutch relay stuck closed (CCRM), or a slight undercharge.

 

[SideSHO09]

Ive got the same problem with mine.
I just replaced accumulator, liquid line w/orifice tube and the compressor.
I didnt flush the system out because the old compressor clutch failed and not the compressor itself so i just replaced the whole compressor.
The system seems to be clean as it has been three days now and it still blows cold air with no compressor lock up.
I charged 134 back in but I am a few ounces overcharged because in the process of trying to figure out why the compressor wouldnt kick on (bad pressure switch plug, now fixed) I lost track of the pressure and put more in after I fixed the bad connection.

Here's the kicker, when I turn on max ac, auto or any other setting that would energize the compressor, neither the fan or compressor come on. I have to keep turning the air on and off until I hear the fan kick on which at which time the compressor kicks on.
When they both come on it blows cold anywhere from 5 to 20 minutes and then the comp. and fan shut off and warm air starts coming out of the vents.

I then have to repeat the on off procedure until it works again.
It seems to be more related to the ccrm rather than a dirty system (orifice tube) or high pressure issue.

 

[rubydist]

The op's symptoms are exactly what I had on my first white 94, and it needed the clutch shimmed. worked great ever since.

 

[Brook24v]

Probably none of the above.

Your symptoms are consistent with evaporator icing. Telltales include a LARGE puddle of water under the evaporator outlet after the car is parked or frost on the evporator to accumulator line.

Typical faults include a cycling switch stuck closed, an AC clutch relay stuck closed (CCRM), or a slight undercharge.

So how do you keep the evaporator from icing over?

The op's symptoms are exactly what I had on my first white 94, and it needed the clutch shimmed. worked great ever since.

Grrrr, I was hoping the clutch didn't need to be touched.

 

[rubydist]

you don't - if its very hot and quite humid, the a/c can run constantly and the evaporator will ice. the a/c needs to be turned off periodically (maybe 10 minutes per hour) to keep this from happening.
however, I don't think that is your problem, I think its the compressor clutch gap.

 

[projectSHO89]

To help differentiate, a clutch gap problem will cause the exact same behavior as if you reached over and switched from AC to VENT.

An evaporator icing event will cause the airflow to become extremely humid and, in many cases, will cause the volume of air thought the ducts to diminish or to stop altogether. If iced, the symptoms will persist until the ice melts. If the car is parked at the time, you will get the aforementioned LARGE puddle of water.

Go do your differential observations.

you don't - if its very hot and quite humid, the a/c can run constantly and the evaporator will ice. the a/c needs to be turned off periodically (maybe 10 minutes per hour) to keep this from happening.

There is no need to turn off a properly charged and operating system. Those don't freeze up.

Here's the kicker, when I turn on max ac, auto or any other setting that would energize the compressor, neither the fan or compressor come on.

Identify your vehicle including whether manual or EATC. There are differences.

 

[Brook24v]

An evaporator icing event will cause the airflow to become extremely humid and, in many cases, will cause the volume of air thought the ducts to diminish or to stop altogether. If iced, the symptoms will persist until the ice melts. If the car is parked at the time, you will get the aforementioned LARGE puddle of water.

That is exactly what I thought, which isn't the case with this particular SHO. That being said, I think it's safe to say that the clutch is needing a shim job.

Edit: I better double check and make sure there is still power at the compressor the next time this car kicks off the A/C. I guess it would be easy to tell if the compressor was still seeing voltage during the random loss of A/C. If it wasn't, then what the **** would be going on? A bad high or low-side switch maybe?

 

[ViPER1313]

Ive got the same problem with mine.
I just replaced accumulator, liquid line w/orifice tube and the compressor.
I didnt flush the system out because the old compressor clutch failed and not the compressor itself so i just replaced the whole compressor.
The system seems to be clean as it has been three days now and it still blows cold air with no compressor lock up.
I charged 134 back in but I am a few ounces overcharged because in the process of trying to figure out why the compressor wouldnt kick on (bad pressure switch plug, now fixed) I lost track of the pressure and put more in after I fixed the bad connection.

Here's the kicker, when I turn on max ac, auto or any other setting that would energize the compressor, neither the fan or compressor come on. I have to keep turning the air on and off until I hear the fan kick on which at which time the compressor kicks on.
When they both come on it blows cold anywhere from 5 to 20 minutes and then the comp. and fan shut off and warm air starts coming out of the vents.

I then have to repeat the on off procedure until it works again.
It seems to be more related to the ccrm rather than a dirty system (orifice tube) or high pressure issue.

My 92' SHO did the exact same thing when I first bought it, it actually turned out to be something with the dashboard EATC unit that had gone wrong or was loose behind the unit. I put in an hard button unit for the aesthetics and ended up fixing the AC in the process :woo-hoo:

Symptoms were that pressing Max AC (or auto, anything dealing with AC) would sometimes cause the AC compressor / fan to turn on, other times all I would get was the blower. When the AC did kick in, it might last for 15 or 20min before it would cut out. On/Off cycling about 20 times could usually get it to kick back on. I always thought that the magnet in the compressor would cut out when it got hot, I was totally off base