1991 Dodge Caravan A/C

We thought our a/c didn't work at all before (Refrigerant perhaps, etc.) but on closer examination when we press the blue button on the climat control panel to turn on the a/c compressor, there is no change in engine tone/the compressor doesn't start. Any ideas?

 

If your refrigerant is low, the compressor won't kick in.

 

Is there a way I can check to make sure that it is not, say, a relay or something, before I get pressures checked?

 

On the firewall, toward the right side is the EXPANSION VALVE. On the valve is a switch with a black rubber boot over it. Unplug it and jumper the two contacts in the boot together.. the compressor should activate. If it does, you problem is most likely due to low refrigerant charge.

 

Thanks for that reply, my memory of my 91' told me thats how i did it, but was afraid it might be wrong.

 

Is there such a device on a '99 Chevy Malibu? My a/c compressor doesn't turn on either.

 

Yes, but it is on the Suction hose, since you dont have an expansion valve......

The older Dodge/Chrysler/Plymouth were simplistic....GM is more technical , and that switch must see other variables in the system in order to get the results you want to see. Its probably better in your case to just skip directly to the pressure testing Part, instead of wasting effort with something that may lead you off in completely wrong directions.

 

Thanks for the information. I'll see what happens.

 

Thinking back.....The switch could possibly be on the suction hose , more toward the center of the firewall. Same black boot, and I believe the wires are DK Blue, and dk blue with White tracer.

 

I do believe I have found the proper area around the centre of the firewall, since I found the black boot there. Just wanted to check, what do I have to use to jumper the boot with? (I'm still new to all this)

Thanks.

 

Cotter pin, coat hanger, paperclip,.....Or A Jumper lead....

Just touch both terminals in the boot to each other..... Start the car and turn the A/C on, The clutch should engage and the compressor should spin...

 

Alright I used a paper clip in both slots of the boot and the compressor did not activate. I tried it more than once and even once doubled the paper clip to make sure it was making contact.. nada. What now?

 

Hello again all, anyone have an idea on this? If it is not low pressure is it possible I just have a blown relay, something disconnected, or a busted compressor button inside the vehicle?

 

BUMP Any ideas? Thanks!

 

You might try running jumper leads direct from the battery to the compressor terminals with the engine off. It will tell you if the clutch is engaging at all. If it clicks, then some component is not allowing electricity to go through. I suspect it's a relay that's bad. Good luck

 

Sorry Codyy...I didnt bail on you...Just replaced My PC....So here I am....

Now......

In the relay center you will find a relay for the A/C compressor Clutch....Possibly labeled "ACC". Dont confuse this with Accesory relay. Remove the relay and flip it over. You will see terminals marked 85, 86 , 87, 87a and 30. In the panel box ...Use your paperclip tho jumper 87 and 30. This should activate the clutch If it does, check for 12 volts between 85 and 86. ,If not check the hot wire from the 30 terminal to the compressor connector, and the A/C fuse.

If you dont have 12 volts across 85 and 86, suspect a bad fuse, or damaged PCM.

A bit of theory---(At least as I remember it-- )

Your Control panel supplies the relay with 12v (+) to activate it. the 12v (-) comes in when the PCM sees the low pressure switch closed. If both signals are present, the relay closes and allows the current to flow thru the relay terminals 87 to 30, and down to the compressor. The compressor it self is grounded thru the Mounting bracket to complete the Circuit.

 

Thanks for the reply from both of you, no problem on the delay.

The test sounds simple enough however I cannot find the relay. My Haynes manual and Autozone both tell me the location, but not which relay is which. In my van, there is no relay box, rather there is 3 relays on the drivers side fender wall near the battery, and 2 on the passenger side fender wall higher up. My Haynes manual did tell me what kind of relays my 3.0 V6 litre engine has, but again not the location.

Thanks!

 

Ouch....that changes things a bit.....

Are the relays "Square Black and Plastic...or "Steel Rectangles"

On a 3.0 MMC motor..the harness connector for the compressor is in plain sight on the passenger side, Just look straight down at the compressor. Match the colors with the relay bank wiring, and pick out your relay.

 

The A/C clutch relay is on the right side (passenger). It is the relay in the rear, toward the firewall.
Hope this helps ya,
Billy

 

Thanks both of you, that should easily narrow it down now. The relays are the black plastic ones too. I'll keep everyone posted on what happens.

 

Okay, I performed the test. The A/C clutch does indeed close when I jumpered terminal 30 and 87. However, when I checked for 12 volts across 85 and 86 with the multimeter, I didn't get anything. You mentioned to check the 30 terminal with something else if I didn't receive 12 volts there - how do I do that? How do I narrow it down between a bad A/C fuse (also where is it located?) or PCM problem.

Much thanks!

 

If the fuse is in the fuse panel inside the vehicle I would need it narrowed down by someone also because I believe my panel chart is inaccurate for my model.

 

No luck finding a certified correct fuse chart, but I'll wait until someone can enlighten me regarding the A/C problem, involving fuses or not.

 

Ok....

Test from terminals 85 and 86 respectively, to positive and negative battery.

Not sure which is which, but one should be 12v (+) from the control panel, and the other ...12v(-) from PCM. If the blower motor works, it is likely that the 12 v (+) is present, and fuses may be eliminated as a source problem. These tests must be made with the engine running and switches in the A/C MAX positions.

 

Thanks for the response. The blower motor does work and I'll update you after I perform the test.

 

ooops.....Forgot something....

While testing......Jumper the low pressure switch. If the car is low on freon, "Jumping-" will prevent you from chasing ghosts.

 

Testing done - Received 13-14 volts from both sides of the relay when testing on positive and negative battery. What now?

 

Does this mean it is my relay or possibly the switch itself?

 

I think I may have over complicated things.......

Borrow a plain old Test Light......With the clip on battery negative, and the probe on either 85 or 86......The lamp must light on one of them.

If it does, put the clip on battery positive. Try the opposing terminal. the lamp should light.

You are trying to determine whether the (+) or (-) side of the circuit is at fault.

My diagrams dont go back that far...but 95 uses the + on 85 and - on 86.

 

This test is to be performed under the same conditions, with engine on and A/C switch on with low pressure switch jumpered?

 

Correct
...........................................

 

Test done. With the clip on negative, 86 lit up. When I switched it over to positive, I didn't get anything on either, but that may be because my cord was short and I didn't get the best grasp on the positive battery terminal.

 

OOps....

I overlooked someone.......

In the front grille, toward the bottom, is an "Ambient temp sensor".....this is the input your computer looks for before enabling the clutch. Jumper it just as you did with the pressure switch........

with both of these switches jumpered, the A/c should activate by the control panel switches.

 

I located the ambient temp. switch, popped off my grill and jumpered it. I also jumpered the low pressure switch just as you said. Fire the engine up, hit the a/c button, and whatdya know the compressor activated! So now, how do I interprate these results?

 

BUMP, don't want the thread to get lost before anyone can respond!

 

Put everything back as you found it......
Start your diagnosis over , starting with the Ambient temp sensor....(Just work backwards from ATS.....) If the compressor operates with ATS jumped, and Low pressure plugged in, your home free. if you still need low pressure jumpered to operate the compressor, the system is low on charge , or the Low press switch is defective.

Just a question, Did it get cold in the car?????? You may still have refrigerant issues, but electrical is almost out of the woods.

ATS is responsible for locking out the compressor when the temp in front of the condenser is below a predetermined temp. For example, your A/C wont work for about 10 or 15 minutes in the dead of winter. When the radiator "WARMS" the sensor, as in stop and go traffic, the defrost setting will cycle the compressor, to defog the glass, without Freezing the moisture first.

Since summer is here, you may "Strip and twist the wires together on ATS, until a junkyard excursion arises, and supplies a suitable donor.

 

Just tested again. The air doesn't work unless the ATS and low pressure switch is jumpered, so that must mean low charge or defective switch as you mentioned. However, it probably means low charge since when the air comes on with both jumpered, the air does not get very cold, and I don't notice a large temp. difference between the compressor plumbing.

Since a/c doesn't loose refrigerant, I must have a leak and that is probably going to cost more than the vehicle is worth.

If you come to the same conclusion as I did, that it looks like low pressure from the results, the only way I could fix it is if there is an easy way to find and repair the leak. As I mentioned the van is not worth it to put a lot of money in.

Its also worth mentioning that I didn't see much of anything moving in the sight glass.

Thanks very much for following this thread!

 

You shouldnt.....if you do, it means there is more space to be occupied by refrigerant.

Since your system is likely still R-12...It would be super expensive to recharge and diagnose a leak. R134a is much cheaper, and there are a number of good Flourescent dye/leak detection solutions available.....Dont give up just yet.

 

The system is R12 unfortunately. The only thing in the sight glass appeared to be a white dot, but I don't know if the glass is broken/scratched or something - either way, it wasn't moving.

What is your best cost effective recommendation at this point?

Once again thanks. Your advice is quality - you should be the next moderator of this forum area.