A/C stopped functioning... probably something simple.

[ceokris]

I've just started getting into A/C systems on vehicles. The other day mine completely stopped functioning ('97 GTS) after my battery went dead., I have a rough idea on how they work but I wouldn't think the battery going dead has any corrolation to the A/C system. Here are the symptoms:

No A/C on any settings. Visually inspected the A/C compressor clutch and it is not engaging ever. The radiator fans do not kick in on any of the A/C settings (which they use too immediately). System blows hot air. However, the system appears to be cycling through the vents properly (ex.. defrost, foot air, vents on the selected settings, and OFF works

Here is what I have tested:

Manually bypassed the A/C clutch relay and the A/C clutch does engage (only tested for a short period of time to prevent damage). So A/C clutch works!

Visually inspected the looking-glass on the AC canister and I do not see any bubbles, actually its crystal clear. So I am assuming its got a full charge.

My real question is, what tells the A/C to start operating? I'm not at WOT, and I'm guessing that disengaging system is tied to the throttle positioning sensor. Or is something telling it to NOT operate, like if there is absolutely no refregerant in the system and there is a sensor for that. It was working perfect the other day, and today it just doesn't want to enable.

BTW, I'm still waiting for my shop manual - if it's anything like the others, I'm guessing it will have little or no information on the air condition system.

Thanks in advance.

-kris

 

[Snake Bitten]

Has that little linkage come off? It's right in front of the heater hose on the passenger side of the engine compartment...

 

[ceokris]

You mean the wire linkage which controls the coolant flow into the heater core? It still appears to be on and is moving to the full extents. BTW, I've also checked the fuse in the engine compartment to the A/C, unless there is another one for the control systems that looked fine.

I'm crossing my fingers and hoping A/C is in the shop manual. I only like to do my own work to the vehicles. I'll have to wait the standard 10 business days for it to arrive.. And I just moved to Tucson AZ, so it's almost a death wish to drive w/o AC

Has that little linkage come off? It's right in front of the heater hose on the passenger side of the engine compartment...

 

[HP]

There is a switch on top of the AC dryer that provides the PCM with
pressure data - if the freon level is too low - it cuts power to the clutch.
The other input that the PCM monitors for AC operation is the coolant temp-
above 235F - PCM cuts power to clutch.

 

[HP]

Try replacing the AC clutch relay - You can use a generic variety from Radio
Shack - for testing - or switch out one of the fan relays.

 

[ceokris]

What would be the procedure to test the pressure switch? I've noticed 12Volts is fed to one lead, and I'm guessing the other is running back to PCM. Higher voltage means more pressure? I'm thinking if I place a resistor across bypassing the pressure switch to see if it engages the A/C. I'm hesitant on closing the circuit completly and feeding a whopping 12V back into the PCM.

Then at least I can either know its the pressure switch, or just plain flat out of coolant (which shouldnt the looking glass appear to be foggy, or bubbly due to moisture entering the system? - which would indicate a leak is present).

Thanks a bunch for the response.

-kris

There is a switch on top of the AC dryer that provides the PCM with
pressure data - if the freon level is too low - it cuts power to the clutch.
The other input that the PCM monitors for AC operation is the coolant temp-
above 235F - PCM cuts power to clutch.

 

[ceokris]

I've tested the AC Clutch relay, also monitored the ground side of it, and its never getting ground signal to activate the relay, so I squeezed a wire in there and tapped it to ground, it does engage the relay and AC clutch.

I'm still amazed on how easy the vehicle is to work on so far

thanks for the bit of advice.

-kris

Try replacing the AC clutch relay - You can use a generic variety from Radio
Shack - for testing - or switch out one of the fan relays.

 

[HP]

You mentioned bypassing the AC clutch relay - So I am assuming the battery power circuit to the relay is reading 12V - correct? Or did you use another
power source to run the clutch?

 

[HP]

The low pressure cut off switch is just wired in series with your AC on/off
switch - so the orange wire is the power input side - and the brown wire is
the output switched power that goes to PCM to tell it to turn on the AC.
If the car is on with the AC knob on - then both of the wires to this sensor
should read 12V.

Let me correct myself on the power flow - the switch to the AC is a ground
switch - so the power source is the PCM - so the power supply for the
pressure switch is the brown wire and the switched side is the orange wire
that goes to the manual AC on/off switch.
I also noticed another switch listed that is series between what we are talking
about - it is listed as a thermostatic switch -

 

[HP]

The best way to check all 3 switches - manual, pressure, thermostatic -
would be to simply turn on the AC and test the grounding wire to the AC switch
if you detect power then the circuit is active - and all is well

 

[ceokris]

It's the pressure switch.. I jumped it and the A/C clutch engaged immediately and the radiator fans kicked in as normal. You guys are awesome!!! So now I'll have to take it in to get the pressure tested or a new pressure switch.

Thanks again guys!

Now its time to hit the local Tucson track for drags.

-kris

The low pressure cut off switch is just wired in series with your AC on/off
switch - so the orange wire is the power input side - and the brown wire is
the output switched power that goes to PCM to tell it to turn on the AC.
If the car is on with the AC knob on - then both of the wires to this sensor
should read 12V.

Let me correct myself on the power flow - the switch to the AC is a ground
switch - so the power source is the PCM - so the power supply for the
pressure switch is the brown wire and the switched side is the orange wire
that goes to the manual AC on/off switch.
I also noticed another switch listed that is series between what we are talking
about - it is listed as a thermostatic switch -

 

[S-JC]

Ah, I love the VCA forums and the wealth of knowledge shared. Here's my story:

On the first hot day this spring, I'm driving my Viper and turn on the A/C. No cold air. Just ambient temperature air. I'm thinking, great, just what I want to spend my time investigating.

Well, I bring the car home, pop the hood, and check to see if the A/C compressor clutch is engaging. Nope, it's not spinning when I set the dial to A/C. Could I have an electrical problem or a bad compressor?

Now, I know nothing about A/C systems. But I'm a die-hard DIYer (one too many ******** shops screwing up previous cars). So I turn to the most reliable source I know--these boards.

Searching the VCA forums nets me the first golden nugget: if the refrigerant is too low, the A/C clutch won't engage. Excellent, I'm thinking. Maybe I'm just out of refrigerant.

Second golden nugget: you can jumper the low pressure switch (take off the little white plug on top of the silver cylinder on the passenger side, which is called the dryer, I've gathered) with a paper clip. This will make the system think it has enough refrigerant and turn on the compressor. What an excellent way to test the compressor and electrical system! As soon as I jumpered it, the clutch engaged and the fan came on. Okay, awesome! Score: VCA--2 points. Unfamiliarity with A/C systems--0 points.

So, I figured the most likely problem is that I don't have enough refrigerant. I went out and bought the self-fill cans (two of them) and recharged the system (way easier than I thought it would be) and now I have cold A/C! Woohoo!

Also of great value is the "I fixed my A/C for $4" thread. I actually got one of those UV leak detection kits (also cake to use) and found that I have a significant leak out of one of the fittings on the compressor. If this charge doesn't hold for a reasonable amount of time, I'll get under there and replace the o-rings.

It took some reading, but all the info you need is on these boards. Thanks, VCA!

 

[dave6666]

Wow. A thread from the dead. Anyway, my '01 is about a 2 can a year leak. Have no idea where it leaks.

2 cans a year? What leak...

 

[EllowViper]

Timely post. I just came out of my garage after doing all that was mentioned above..with service manual in hand. Still no A/C Clutch engagement (although I did not jump the relay in the fuse block..I'll try and force 12v to the clutch by bypassing the relay). I did swap relays and fuses out with no change. System is charged, fan come on as expected both with the dash switch and jumping the dual pressure switch. Just cannot get the clutch to engage (you can usually hear it very well when it kicks in) I see nothing in the sight window on the drier so I know the clutch is not engaging and no fluid is being pumped. Worked fine and then one day no A/C so it wasn't a case of it simply getting warmer by losing refrigerant. These Gremlins ****!!

 

[Tom F&L GoR]

Timely post. I just came out of my garage after doing all that was mentioned above..with service manual in hand. Still no A/C Clutch engagement (although I did not jump the relay in the fuse block..I'll try and force 12v to the clutch by bypassing the relay). I did swap relays and fuses out with no change. System is charged, fan come on as expected both with the dash switch and jumping the dual pressure switch. Just cannot get the clutch to engage (you can usually hear it very well when it kicks in) I see nothing in the sight window on the drier so I know the clutch is not engaging and no fluid is being pumped. Worked fine and then one day no A/C so it wasn't a case of it simply getting warmer by losing refrigerant. These Gremlins ****!!

What do you see in the sight glass when the pressure switch is jumped and the compressor running? (Why do you think it's fully charged?) If lotsa bubbles, maybe you are still low.

 

[EllowViper]

No bubbles or anything..looks bone dry. The pressure on the low side port is actually a little high... When I hook the gauge up when its running, the indicator is in the yellow "caution" area of the gauge. The gauge has low-normal-caution-dangerous readings...green-blue-yellow-red. I had bled out all the charge manually (a lot of refrigerant in these systems) and recharged to the same pressure reading but the compressor clutch still does not seem to be coming on (even with the dual pressure switch bypassed). In looking at my manual, the thermal switch is located before the dual pressure switch so that seems to be operating otherwise there would be no juice to the dual pressure switch. At this point, I need to get voltage right to the compressor to determine if the clutch assembly actually works..thus my plan to bypass the relay as mentioned above. The service manual has some pretty good diagnostics but at this point they are all leading me to verify clutch functioning before I look elsewhere. All in all its a pretty basic design but verifying operation of the descrete elements is the troublesome part.

 

[dave6666]

***** living in these states where we actually have summers...