2G AC Pulsing

[kingje1]

HI all, when I turn my AC on It pulses about once a second. I feel the pull on the engine with every pulse. Coldish air comes out but it's not cold enough to keep me cool in the southern heat.

I'm sorry if this has been answered before, I've been looking through threads and searching now for 30 minutes but haven't found the answer. I am Gen X so forums and tech comes a little harder for me.

Here is what I have done so far:
1. Checked the connections for anything obvious like exposed wires etc and found nothing.
2. Checked the pressure and added until it was good. Air got cooler but still not cold enough.

I've been blessed in the past with cars that have not had issues with AC any more than slight leaks.

I would appreciate any help or a link to a thread that could help me.

 

[Dericsh]

Some good things to check off the list now.

Although the evaporator core probably could use a good cleaning at this age, I think the consistent voltage from the ACCU output rules out a temperature fault inside the evaporator.

 

[chrysler kid]

Some good things to check off the list now.

Although the evaporator core probably could use a good cleaning at this age, I think the consistent voltage from the ACCU output rules out a temperature fault inside the evaporator.

Sorry sorry sorry think I mis stated my point

Replace the expansion valve

Then clean the evap core because you have to remove it anyways

The expansion valve being faulty is my main area to concentrate. The clutch is cycling because of a cut of 12 volts from the pressure switch. The pressure switch is cutting voltage because of an actual pressure problem.

Tried to find viable search results on this forum for ac issues and literally not any threads with solutions. I think this site and user base being in the midwest really means the forums really dont care about AC that much. So I wasnt able to find any answers to deny or enforce my claim, I also didnt find any results from people replacing the accu. The most i could find is that the accu fault usually results in a flashing AC light button on the ac switch on a 2g

So the only advice I can offer is they same advice that has always worked for me in all of my dsm's. Since im from the south and always drive shit boxes i always have the same process, even with my dsms.

Problem: shit box has no AC
Shit box has good compressor
Shit box has good ac condensor fan
Shit box ac kinda works but not really

Then proceed to replace parts that fail due to age and end of life:

Replace the drier
Replace the expansion valve
Replace all o rings connections
Vacuum the system to -28hg
Fill the system with 18oz of refrigerant (or low side pressures based on ambient temp readings)

I get you want to trouble shoot electrically but these diagnostics are beyond what any tech service at a shop or even the dealer would offer.

 

[kingje1]

OK, so first, I apologize to everyone for taking so long to get back to this issue. I hope you didn't think I abandoned it. I've been working on my 420a car because I need to sell it and it's almost done, then I sold my GTO, bought an B8.5 S4 and have been doing a LOT of mountain biking. Anyway, something that's been nagging at me has been what if I have not been running the right volume, so I evacuated the system and jumped the compressor until I got the 26 oz in it. Sure enough, I still have the pulsing. Now that I have completely troubleshooted all the electrical issues, it's time to start replacing some stuff. I ran a vacuum and it held the vacuum for an hour afterward so I feel like the system is tight. I'm going to do what Chrysler Kid said and replace the drier and expansion valve. I'll let you guys know how it goes.

 

[Sirius1995]

OK, so first, I apologize to everyone for taking so long to get back to this issue. I hope you didn't think I abandoned it. I've been working on my 420a car because I need to sell it and it's almost done, then I sold my GTO, bought an B8.5 S4 and have been doing a LOT of mountain biking. Anyway, something that's been nagging at me has been what if I have not been running the right volume, so I evacuated the system and jumped the compressor until I got the 26 oz in it. Sure enough, I still have the pulsing. Now that I have completely troubleshooted all the electrical issues, it's time to start replacing some stuff. I ran a vacuum and it held the vacuum for an hour afterward so I feel like the system is tight. I'm going to do what Chrysler Kid said and replace the drier and expansion valve. I'll let you guys know how it goes.

If you managed to pull vacuum I assume you have r134a gauge set too, post a picture what gauges say when car is running ac full blast, that should tell everything we need to know before replacing parts you don't have to replace

 

[kingje1]

Hey Sirius, check out the videos on page 2, that is how the gauges are reading. Thanks.

 

[Sirius1995]

Hey Sirius, check out the videos on page 2, that is how the gauges are reading. Thanks.

Is the AC clutch kicking on and off or is it on all the time? And is the second fan for condenser on?

 

[kingje1]

The clutch is kicking on and off. It only does it when there is enough freon. I started letting some out and it stopped pulsing once I let a little more than half of it out. When I was refilling it with the relay in it started doing it again once I got about 12 oz in it. I had to jump the compressor at the relay to get the rest in there. I pretty much knew it was going to do it but I wanted to at least cross that off the list of diagnoses. The condenser fan does come on.

 

[Dericsh]

I'm going to do what Chrysler Kid said and replace the drier and expansion valve. I'll let you guys know how it goes.

I think you’re on the right track.

 

[kingje1]

I was surprised at how easy it was to get to the cooling unit (evaporator, fin thermo sensor and expansion valve) . Here's the steps as I couldn't find any instructions anywhere
1. Remove the center trim panel on the passenger side
2. Remove the glove box (two bolts once you drop the glove box all the way down)and the bracket that the glove box bolts into (two phillips bolts and two 10mm bolts)
3. Unplug the three electrical connections on the cooling unit and disconnect the wire loom from the top of the dash so you can move it around.
4. Disconnect the cable that runs across the cooling unit (I think it controls the recirc door)
5. Make sure your AC system is fully discharged, then disconnect the two lines on the firewall behind the battery
6. There are three bolts for the cooling unit, two on the top that bolt upwards and one nut underneath the cooling until on the firewall.
7. Once all this is done you will find that it's loose so it's just a matter of finding the right way to move it around to get it out.

 

[kingje1]

Here are pics of what I pulled out. I got the wrong expansion valve so I had to order another one.

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[kingje1]

Hi everyone, I am sad to report that the expansion valve and drier have not solved my pulsing issue. I continue to get the switching on and off but with slightly cooler air now. If anyone has suggestions I am all ears.

 

[Dericsh]

Let’s take a step back now, with a fresh vac and charge, what are the gauges reading?

 

[chrysler kid]

Hi everyone, I am sad to report that the expansion valve and drier have not solved my pulsing issue. I continue to get the switching on and off but with slightly cooler air now. If anyone has suggestions I am all ears.

What is the low side pressure reading when the ac clutch clicks and turns off?..

Typical readings would be low side 40 to 45 psi

If the low side clicks on and off, the readings will go from 70ish psi and click the compressor on and you will get a reading of 55psi and the compressor clicks off. This is the switch cutting power because the low side pressure is too high

If you take a reading and the low side pressure is 40psi and the compressor clicks off and then reads 60ish or something psi then you can have another issue. Low side pressure should be 40-45 psi and the compressor should not click off

I will discuss how to bypass the switch to keep the compressor turned on to verify there is constant signal from the dash; after you have verified low side ac pressure when the ac compressor clicks and turns on

 

[1990TSIAWDTALON]

I don't go by this chart "religiously", but I do reference it to see how close or far off the system is.

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[chrysler kid]

Since you seem to take a while to respond ill also post the link for free factory service manuals.

I skimmed through them the other day and they are comprehensive for testing and diagnostics
Www.charm.li

Next thing for me to tell you to check is the pressure switch if you have verified the low side pressure is 40 psi compressor engaged

The compressor switch should be recieving 12v constant source power

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