A/C straining and killing engine

[burch]

Hello everyone -

I’ve got a recent issue with 6631, that I believe is electrical, but wanted to check with the group. This one seems to center around the A/C system.

When I start the car from cold, voltage gauge reads about a needle-width above 13. I turn on A/C, car dies immediately without application of throttle. When driving, this feels like you are towing something that is shaking behind the car. My first thought was that I may have some sort of mechanical issue at the A/C compressor. PO changed this to an R134 system, but I do not know how long ago. Removed the A/C belt, and checked all idler pulleys for resistance….everything was good (just replaced the idle pulley bearings last summer). With the belt removed, I repeated the test, and the same symptoms appeared.

Drove car around for a bit to warm it up, acceleration was a bit sluggish. Slightly improved as the temperature approached operating temp.

Drove the care with A/C off until otterstat activated the cooling fans. Fans come on, voltage drops to about a needle-width under 13. Put car in park, needle stayed approximately the same. Fans do their thing, drop the temp down, and they shut off. I turn on the A/C. A/C fans turn on (sans compressor), and very little drop in voltage. Cooling fans, however, did not come on with A/C. Turned car off.

Turned it on about 10 minutes later. While idling, I turned on the A/C (with the belt still off). Voltage dropped to about the halfway mark between 13 and the hash between 13 and 8, but car continued to idle smoothly. Put the car in reverse, and voltage dropped and the car died.

I checked the two major ground points (drivers side radiator bracket and trailing arm bushing mount). Cleaned both, and tested via multimeter. 0 ohms of resistance, so I believe those are ok. Checked the relay/fuse compartment, no melting or anything at the fan fail or cooling fan relay socket. There was a little bit of plastic melted on the top connection to the cooling fan breaker, but it didn’t look recent.

What do you all think? I believe I have the original alternator, which would be Motorola based on VIN. I’ve never had it out, and can only see part of the blue and silver label on the top. The alternator seemed like a possibility, although if it were at fault, would I ever see the voltage that I’m supposed to?

[Bitsyncmaster]

Check your battery voltage with your meter. A good alternator should provide about 14.5 volts.

You have another problem if your AC compressor turns on and the fans don't. Check the diodes in relay compartment harness.

My guess is your alternator is bad.

[David T]

Check your battery voltage with your meter. A good alternator should provide about 14.5 volts.

You have another problem if your AC compressor turns on and the fans don't. Check the diodes in relay compartment harness.

My guess is your alternator is bad.

Agree with checking the alternator and will add check the battery too. and it also sounds like the A/C could be overfilled with refrigerant.

[burch]

Alternator surprisingly tests good! about 14.10V with car running. Will check diodes and refrigerant next, and see what we get.

[burch]

Diodes tested good, and the connections were clean and tight. A/C shows a little bit of an undercharge, and the clutch engages intermittently, supporting that reading. Probably wouldn't be a bad idea to evacuate and charge the system properly, as I don't know the history of that specifically.

So, at this point...

Grounds = OK
Alternator = OK
Cooling Fan Diodes = OK
Relays and Breakers = Appear to be ok

Still seems to have to be electrical, as I was able to replicate with no A/C belt.

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

[Bitsyncmaster]

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

I've not seen an alternator fail intermittently but I would guess it can happen with the regulator with temperature changes.

[dn010]

lack of oil in / or tired compressor would be my guess.

Sent from my XT1254 using Tapatalk

[DMC-81]

Hmm. So you are able to replicate the shaking/ sluggishness during a heavy electrical load with and without a A/C belt installed, and the symptoms improve as the car comes up to operating temperature?

If so, I wonder if it could be related to the ignition or lambda systems?

[burch]

It is a possibility. Seems like this is an issue where I'll learn to troubleshoot a bunch of things. Anything I should check to make sure those are operating correctly?

[David T]

Diodes tested good, and the connections were clean and tight. A/C shows a little bit of an undercharge, and the clutch engages intermittently, supporting that reading. Probably wouldn't be a bad idea to evacuate and charge the system properly, as I don't know the history of that specifically.

So, at this point...

Grounds = OK
Alternator = OK
Cooling Fan Diodes = OK
Relays and Breakers = Appear to be ok

Still seems to have to be electrical, as I was able to replicate with no A/C belt.

Could a failing alternator be problematic intermittently, or once they start to go, is it pretty consistent?

The clutch is SUPPOSED to engage and disengage cyclicly. It should run pretty continuously at idle but engage and disengage when above idle, quicker the faster it runs. When the clutch engages the cooling fans also start up so it is a big load on the electrical system and a big drag on the motor at the same time. If everything is not running right it could cause the motor to stall out. The idle motor system is supposed to keep the RPM's steady. Vacuum leaks can cause all kinds of problems made worse when you run the A/C.