I just replaced the alternator and the serpentine belt. When I started her up (1987), there was a distinctive "click" about every 5-10 seconds. I looked and what I assume to be the A/C compressor clutch was popping out (to the front) and would stop turning, then would pop back in. (Is that even the clutch I'm seeing-I'm not sure). And the A/C, which was operating before, is not blowing at all inside the car. I checked the belt and cannot see that it's not on properly but the tension marks were outside the parameters with the new belt. So I put the old belt back on and, while the tension mark was centered, the same thing was happenong vis-a-vis the front of the compressor. Have I (hopefully) made some simple error or put something out of the norm. Any ideas?

Jim
1987 C-4

 

The magnetic clutch is on the front, yes you are seeing the clutch plate engage and disengage. Could be cycling on a pressure limit switch ... ie low freon (low pressure) high discharge pressure ( no air across condenser) or perhaps low pressure due to no airflow across evap coil. You mention no air blowing in the car ... do you mean no cold air or just no air at all from the vents? Did you disconnect the blower motor or perhaps a vacuum line???? ............. signed ..... short time C4 owner .......... long time a/c guy ...............

 

Thanks for the reply. There's no air blowing at all through the vents now - only variable being the new alternator and belt. Your idea of my accidentally disconnecting a swith or hose makes sense. I'll look closely.
I still can't figure out why the new belt should be outside the tension marks but the old one isn't and wonder if that's related.
Thanks again.

JM

 

The clutch cycling is normal. The fan is a separate problem. I would guess that you dislodged or left something loose.

 

..huh?..while cycling is normal to keep the system from freezing, it is not normal at every 5-10 seconds......sound like low refrigerant charge or bad lp switch....

 

A properly operating system will not have the clutch cycling any where near that often.

 

Bummer - Can't imagine any disconnected switch or faulty wiring causing it to rapidily cycle (specs are 8 or less per minute at 70 degrees). Did you break or kink a line? Any hissing? Any ice forming on the lines close to the compressor?

 

Thank you all for the posts and advice, gentlemen. The cause of the clutch engaing and disengaging appears to have been that the blower motor wasn't running. The fix - though it isn't one - was to recycle the battery.
I've owned the car since new and have had all the familiar electrical gemlins one of which was that, after disconnecting the negative terminal for various reasons, when I turned the ignition on, the blower would always be going. Yesterday, after installing the alternator, I reconnected the battery, the blower came on, and I shut it off. For some reason, then, when I started that car, the blower wouldn't come on when I tried to get it to. So, this morning, I disconnected and reconnected the battery and, as usual, the blower came on, the A/C worked fine, the clutch acted properly. For what its worth, I've tried to trace the electrical problem and had "experts" try, too, to no avail (and at some expense).
Again, thanks for the help and advice.

Jim

 

Weird - Sounds like you need a new Blower Module or it has intermittent power/ground. This device, for your Year, provides a ground for the compressor clutch and controls Blower Speed. Given that disconnecting and reconnecting the battery gets things going again might possibly point to the Dash Controls (which has a memory function), but I'd start with a couple of checks at the Module first. It's on the left side of the Evaporator Case. Here's a little about how it works:

To control Blower speed, low voltage signals are sent from the Controls and then amplified and sent on to the Blower Motor. Actual (amplified) voltage at the Blower Motor is returned to the Dash Controls so the Controls know what the Motor is spinning at. That's on a fused 5 amp circuit which is mounted on the Firewall to the left of the Evaporator Case (leads will be the same color as what's hot at the Blower - purple or black/red). When that fuse opens, you usually get nothing but high blower and it may run with the ignition off. I'd check the Fuse, but a problem here shouldn't effect Compressor engagement.

Next, the Dash Controls send an a/c request to this Module whenever you select the Auto/Defrost/or BiLevel settings which then grounds the clutch coil. The signal is only sent AS LONG AS a separate circuit from the Controls is grounded through the High Pressure and Low Pressure Switches AND another circuit is grounded at the ECM (for idle and WOT control). If either of these latter circuits are open, the ground signal is removed from the Module and the clutch disengages.

Generally, the ECM circuit, when faulty, causes the idle to go to hell and you end up with surging and stalling. And the low pressure and high pressure switches usually work or they don't (and if the high pressure switch fails to open - should it ever reach the blowup threshold - you end up with a hole in the hood). And a faulty low pressure switch makes ice or it simply doesn't work. Yours sounds like it's working normally, only indicating that the charge is low and it's not.

That leaves the Module - intermittent power - which is battery voltage from a fusible link either behind the battery or at the Starter. It's red - wriggle it around. Without power - nothing works. Ground - spliced to the Blower Motor and terminating on the frame below it - same result without it. Some some sort of cracked solder joint in the Module board - you could aim a hairdrier at it, but I wouldn't overdo it as there is a big heat sink to keep it cool and it's mounted right in the Evaporator air stream, so the Engineers want it to stay cool. If all of your checking doesn't produce anything that duplicates your problem, you might just want to replace the thing anyway - failures are fairly high (on the Blower not compressor side) - but it is a 100 Buck part.

Dash Controls - when it comes to the Compressor circuit, a bitch to diagnose because you've got to have all the other circuits - pressure sensors and ECM - completed for the Controls to send a ground signal. If you've got a scanner, it's a lot easier because you can see what the ECM is seeing and if your fairly confident that there isn't a high or low pressure problem, jumper those switch harnesses with a paper clip. Then look for the ground signal at the Module - about 6 volts on the Green/Yellow wire. Then, if the voltage starts flashing back and forth , you know it's either the wire (wriggle it around) or the Controls. Separate circuitry is used to control the Blower, so it would seem rather remote that you would lose both without the Panel going blank.

Hope this helps.

 

SunCR:

Thanks. I've printed that out and need to study it for a while. I've had a continuing problem with the display readouts so it may be related to other things and what you say makes sense - to the extent I'm capable of grasping it -which is in question.
Thanks again.