A/C Problem

[aualexa2]

Hi guys,

I've searched the forums and I have a Bentley, so I'm going to go through the regular steps of working up a non-functional A/C, but I wanted to post the symptoms the car has been having and see if they sound familiar to anyone:

Started out that when I turned on the blower motor, it wouldn't turn on at the lowest speed. I had to turn it on the middle speed or the highest setting to get it started. Once started, I could turn it to the lowest setting and it would work. The next thing that happened a few weeks later was that it would intermittently stop working. This was usually when the car was stopped at a light. When I started to accelerate, the fan would go full blast, and then slow down to normal speed. Finally, today, the blower stopped functioning all together. Only thing I've done so far was check the fuses, and they seemed fine. I replaced the fuse for the A/C anyway b/c it looked old and was probably last changed years and years ago. The condensor blower motor was replaced less than a year ago.

I'm going to start testing the individual components of the AC system (start wit the evaporator blower motor?), but if this sounds familiar to someone and they can offer a little guidance, it would be appreciated.

Thanks!

[p911dad]

This may be a result of a failed bi-metallic switch in the a/c system. It is found in the intake port of the evaporator, located in the footwell on the passenger side, up in the front bulkhead or "firewall". This controls the blower switch (low, medium, hi speeds). It is also called the blower resistor. I'm not expert for sure, but I seen this fail on several cars in the past. It is a real head-scratcher, and was diagnosed for me in the dealership.

[Bob Kontak]

See post number 9 in this link. It talks of the resistor going bad will not allow the fan to run on low. I think gmeteer is steering you straight.

95 993 condenser and oil fan issues

[aualexa2]

Found the section in my Bentley manual on A/C blower resistor pack. "If the evaporator blower works at the maximum setting, but not in A/C blower switch positions II and III, test resistor pack". Now, I know where to start. Thank you, guys!

[Bob Kontak]

Cool - Let us know how it goes - Helps others that will have the same problem in the future.

[DRACO A5OG]

Originally Posted by gmeteer

This may be a result of a failed bi-metallic switch in the a/c system. It is found in the intake port of the evaporator, located in the footwell on the passenger side, up in the front bulkhead or "firewall". This controls the blower switch (low, medium, hi speeds). It is also called the blower resistor. I'm not expert for sure, but I seen this fail on several cars in the past. It is a real head-scratcher, and was diagnosed for me in the dealership.

+1 on the Bi-Metalic Switch, check the contact to insure there is no corrosion there. Not sure how to check if the switch is bad but that switch does control the speed. It sits right next to the water drain off and if you live in a rainy climate, it could get wet.

I've sealed that area except for the drain for extra measure.

After that I would check the relay in the smuggler's box. My relay was buzzing like crazy and tripping my fuse. I removed and tapped on it. apparently it was getting stuck in there. I ordered a new relay but the buzzing and fuse tripping did not re-surface. All COOL Now

[wwest]

Originally Posted by DRACO A5OG

+1 on the Bi-Metalic Switch, check the contact to insure there is no corrosion there. Not sure how to check if the switch is bad but that switch does control the speed. It sits right next to the water drain off and if you live in a rainy climate, it could get wet.

I've sealed that area except for the drain for extra measure.

After that I would check the relay in the smuggler's box. My relay was buzzing like crazy and tripping my fuse. I removed and tapped on it. apparently it was getting stuck in there. I ordered a new relay but the buzzing and fuse tripping did not re-surface. All COOL Now

The low/med speed controls consist of two fairly high power consumption nichrome wire wound resistors mounted within the cabin air return duct to the evaporator fan inlet/suction side.

These resistors can/will get VERY hot if there is not sufficient airflow over them. Hot enough to start a fire so the bi-metallic switch contacts are used to open the low/med speed circuit if the resistors begin to overheat.

The first thing to do is make sure you have a FREE/open/unblocked, airflow path throughout the A/C airflow ducting. A partially clogged evaporator itself is not out of the question as is the possibility of extreme dirt deposits on the squirrel cage blower fan vane surfaces.

Back in my USAF days ('57-60) we always carried small files to clean/clear/burnish relay contacts such as these. Use a little emery cloth to burnish the bi-metallic switch contacts and all will be well again.

[aualexa2]

So, I started by checking for current to the evaporator blower motor and there was none. I then went to the passenger footwell and exposed the bi-metallic switch. I unhooked the wires from the bi-metallic switch, and when the speed setting was on II and III, there was current (around 5 volts) in the appropriate leads. So, I guess that means everyone was correct and the bi-metallic switch is bad, right? I'm going to post a wanted ad in the parts section. Anyone have pictures or instructions on how to replace it?

[Bob Kontak]

I would read what wwest says to do in post number 7. The price for the repair sounds pretty reasonable.

[aualexa2]

I tried cleaning them off as wwest said. Unfortunately, no luck. Hopefully, someone will have one that they no longer need.

[Bob Kontak]

Should not be hard to source one used.

While you are in the foot well, and after the resistor part is out, I think there is one more part you can remove through the hole and get to the bottom of the evaporator. I did that to mine and found there was fuzz, human and dog hair and stuff caked on the bottom. I just used 409 to soften it up and then used a light touch with a rag to clean the debris off and then vacuumed it out best I could It made a difference in air flow.

[aualexa2]

Thanks for the tip! Hopefully, I'll find a replacement before the weather gets really hot. I'll keep everyone updated once I get it replaced.

[aualexa2]

The saga continues... Is it possible that everything in my A/C malfunctioned at the same time?!?

To recap, I started by checking current at the wires leading to the evaporator blower motor, and there was no current. I also replaced fuse #2 even though it wasn't blown (it just looked old). Next, I went to the resistor pack (bi-metallic switch), and there was current in the appropriate wires. So, I figured the bi-metallic switch was the problem. I cleaned the leads (as wwest recommended), but the blower still didn't work. As I was trying to find a replacement resistor pack, I decided to recheck for current at the blower motor. Now, there was current, but the motor still wasn't running! I was able to find a replacement motor that was tested by a Rennlister and was functional. Before I installed it, I hooked it up to the wiring in the car and tried turning it on...nothing. I then tested it by hooking it up directly to the battery, and it worked (For ****s and giggles, I also hooked the battery directly to my old motor, and it was dead). I started wondering if there could be a bad ground, and as I was looking at ground G104, I saw that the new fuse I had put in was blown! Replaced the fuse, hooked the new motor up, and now it runs! Crazy. So, I'm thinking that my bi-metallic switch and my blower motor died at the same time. That's why I wasn't getting current to the motor until after I cleaned the leads, and then once current was restored to the motor it was working because it had seized up.

Anyway, I have the functioning motor ready to be installed. I just need to remove the old one. From what I've read, I think I can do this without removing the evaporator or disconnecting any refrigerant lines. I just need to remove the connection to the air duct, remove the support brackets, pull the evaporator temp probe out carefully, remove the spring clips without dropping them, free up some of the insulating tape that has become molded between the blower housing and the expansion valve, and then slide the top housing that contains the motor out. Does that sound right?

Another question: when I had the replacement motor hooked up, I turned on the A/C control knob and the condensor and the condensor fan came on, but turned off after a few seconds. Is this normal?

Sorry for such a long post. I'm a total newbie to this stuff, and it's been a real pain the rear figuring it all out.

[RSTarga]

I don't believe you can do the motor without removing the evaporator box. I recently replaced my fan switch and found that the fan runs much better now, they run really hot and tend to burn out slowly.

[aualexa2]

RSTarga, the evaporator box is what houses the motor, right? If so, I know that I need to remove the top half of the evaporator box. What I'm not as sure about is whether or not I need to remove the A/C expansion valve which would require removing the refigerant from the system. If possible, I'd like to avoid having to do that.