Airbag/A/C problems..??

--------------------------------------------------------------------------------
Hi,

I know there are some pretty knowledgeable people on here, so I figure I'll get an answer or two. I've got a 98 Mountaineer, 5.0, AWD. Has 176K on it and still runs fine, recently replaced the tranfer case, but other than that it's pretty much the way it came out of the factory. Here's my problem: Had a Airbag light come on flashing a "12" code. So I replaced the fuse in the power distribution box, now I get a code"52". I guess that's because I replaced the fuse without disconnecting the battery ? So I'll have to get the dealer to reset the light for me, or wait the 256 starts to get it to go away. But at the same time the airbag light went on, my A/C quit working too. I've checked the freon level and it's fine. The A/C clutch kicks in runs for a second, then kicks off repeats forever. Everyonce in awhile it never even kicks in.

Is there any connection between the two systems that might cause this...? Or is it just a coincidence that they both went at the same time? I'm kinda hoping that once I get the airbag light reset, the a/c will go back to working? I know...what are the odds....I can hope can't I ? Any insight would be quite helpful...thanks in advance....

Oh yeah, it's a manual system, not a climate control system.

The themal fuse in the diagnostic moniter is blown. A backup power supply is contained in the monitor of at least 23 volts, If not the diagnostic trouble code 52 will flash. The voltage boost circuit in the monitor is damaged and the monitor will have to be replaced. It's a long shot but disconnect the negative terminal on the battery for 15 minutes and see if it resets the light. I can't find it, but the thermal fuse can be replaced. Search the forum for "Thermal fuse air bag diagnostic monitor"

I don't think the thermal fuse is considered a "user serviceable item." The expected repair is to replace the module like Davescort initially suggested.

As for the A/C cycling rapidly, the two symptoms are likely coincidence. The rapid cycling would typically suggest a low charge. How are you determining the system is properly charged with R-134a? Are you using a gauge set and monitoring the high and low pressure sides at the same time? If you are and both side are definitely properly charged, then you might have a problem with the low or high pressure switches. Did you by chance jump start the truck just before these issues began, or did something else happen that may have caused a voltage spike on the system such as welding in a patch panel, etc.?

-Rod

Thanks for the info. I checked the freon level with a gauge on a recharge kit. It showed that the system was at the high end of the filled level. With the truck running, the gauge showed pressuring increasing , then a rapid decrease and again a steady increase and a release. I think this is what the system is suppose to do...? Someone suggested that perhaps the low pressure switch might be the culprit. So I unplugged the connector and jumped it...started the car and the clutch kicked in and ran continuously. Am I correct in assuming that the switch is bad...?

I'm looking into the monitor for the airbag and will let you know what I find out. I did read somewhere that the light could be reset by the dealer, and that if the system was fixed by replacing the fuse, the light would stay off.

Thanks for all the info.

quick update: Took the truck to a mechanic and he connected his Star unit with the proper module and got the error codes that were stored for the airbag problem. Guess what, a direct short to ground caused the fuse to blow.....anyway, clearing the codes, no more flashing airbag light. Light comes on during startup, does it's self diagnosis, and turns off like it's supposed to. I imagine this scenerio might repeat itself at some point in the future, but for now all is working fine.

A/C is still a problem. I replaced the low pressure switch, and then hooked up the recharge kit to it again. gauge on the unit shows "filled", I strted the truck up and watched the gauge.....it would go up to the "alert" area of the gauge(about 65psi) and then drop down to about 25psi and then start to build again......just took a few seconds and it keeps repeating this. I'm taking it in to a repair shop tomorrow and getting it diagnosed....hopefully it's something simple....I'll report back what is discovered.

The system will also have a high pressure switch which will cause the clutch to disengage for high pressure too. If the system is overcharged, you might get this scenario. That's why you really need to monitor the high and low pressure sides at the same time to determine if the system is overcharged, undercharged, has a compressor issue, or a restriction in the system. Taking it to the shop, such as you are, is probably the best solution. Good luck!

-Rod