How to test AC Evaporator fan - not running

As I restore the 996 I got, it seems its 2 steps forward 1 step back! Now that I'm moving to restoring the interior, I was testing the HVAC system before I put my new dash in. As others suggested, check for foam and sure enough it all deteriorated. I replaced all that and testing the AC it is not working, and today its in the 90s!!! Went over everything in general, and discovered that the EVAPORATOR FAN at the front is NOT RUNNING at all. I checked FUSES and RELAYS and everything is ok. I would think that the next step would be to test the actual fan itself???? I've looked everywhere and cannot find any info on testing the fan. Can anyone tell me how to TEST THE EVAPORATOR FAN at the front? Can something be jumped to test? I did find a lot of info about RESISTORS go bad, but I'd like to test the FAN first. Also is there a way to TEST THE RESISTER before replacing? And finally, I have not checked the compressor clutch. Would a problem with the COMPRESSOR have any effect on the AC EVAPORATOR FAN not running? Thanks!

Quotes source post: 20083140

Are you talking about the radiator/condensor fans or the blower that draws cool air from the evaporator in the cabin?

Quotes source post: 20083162

No, the evaporator that's located on the driver side, at the FRONT of the car located near the bumper. There is a fan that blows air through the AC evaporator that cools the AC gas. You can see the evaporator if you look in the opening of the bumper. There is a fan that pushes air through it to cool the AC gas. Mine is not running at all. I'm assuming I'm using the correct terminology!

Thats the condenser fan, those are condensers nor evaps. Evap is in the dash. A obd tester should be able to cycle the cond fans.

Right.....I just found it as you replied. I'll try with my OBD again, I dont recall seeing that option but I'll check again and report back. Thanks

I just discovered that my compressor clutch is not engaging. I thought it was but is not. If the compressor is not engaging would that fan still run? Wondering if I have multiple problems or if no engaged clutch prevents condenser fan from running?

Quotes source post: 20083202

In my expereince with auto A/C in general, it's low pressure (lack of refrigerant) in the system that shuts the clutch off. I would take a pressure reading on the low pressure side and if indicated, add R134. Then the clutch should engage when you turn the A/C on. However, the fan should come on with or without A/C when you turn the fan up using the controls in the console. As you say, you might have 2 problems. Don't forget to check the appropriate fuses! Good luck!

And another thing! You mentioned resistors ( that relate to the fans drawing air across your A/C condenser and your radiators.). I think mine are going bad, so I just bought a couple. I can't hear my low speed fans coming on, but the high speed works. (Same fan, 2 speeds due to the resistor wired in). When the resistors go bad, the usual symptom is just that: high speed works, but low speed doesn't. Independent of your blower motor's woes and your A/C clutch, the fans at your radiators should work as the factory intended. (They come on low when you turn your A/C on with coolant below 206 degrees, and they turn on HIGH when the temp exceeds 206 with or without A/C.) If they don't, you could be looking at replacing the resistors!

I finally accessed the back fuse box panel behind the seats. Took my over an hour because the top does not work and I dont think it was used for at least 10 years. Pulled open the carpet where the 2nd fuse panel is, was not easy because you have to put your hands under the convertible top reaching in to the area behind hte seats to access the fuse box. I'll try to post some pictures. Pulled the relay for the AC compressor and jumpered 87 and 30 which should have forced the clutch on the compressor to engage and NOTHING. I nearly cried! So now I'm not sure what to do next, might be a sensor, maybe the high pressure sensor in the frunk near the AC ports, who knows, but after a long day in 90 degree heat I'm done screwing around with the AC. Going to just concentrate on the interior of the car for now, and if I get that all in order at least I can drive it in the fall and winter until I get around to spending the $1000+ on AC. Then God know what to get the top working, nothing seems to engage so its probably a top to bottom redo. Now its time to have some still cold beverages!

Quotes source post: 20083398

I think the refrigerant is low too.

Quotes source post: 20083577

It was but I checked it using a refill that Ive used many other times on other cars, and filled it to the upper normal level and still nothing. I'm going to order some pressure gauges and test the high pressure side. I dont have a gauge for that.

Quotes source post: 20083732

If you filled to 'upper normal level' (what ever psi # that may be ?) (on any port/service valve) with compressor not pumping, the same exact pressure will be on both the hi & low sides, so thats not your problem if system is truly topped off.? So you say it was low on refrigerant..? thats at least 1 problem you need to solve and find the leak. If the system is filled to normal pressures with compressor not pumping, the clutch should engage. If you just dump in some refrigerant till the pressure goes up, the clutch will turn on at least momentarily(maybe just a second or 2) till compressor pumps down the pressure under the low pressure switches limit. To get above low pressure cut-off, you need close too full charge pressures with compressor running. Not sure how you could charge the system without the compressor on and pumping..? Unless you evacuated the system, vac'd it down and dumped in a full weight charge, did you do that..?

Quotes source post: 20084103

When I put the refrigerant charge on the low side, the gauge read low. At the time I thought the clutch was engaging. With the car running and the AC set to high I added the refrigerant until the gauge reached the upper area in the green, pausing along the way to see if the AC was cooling, but no effect noticed. The clutch never engaged as far as I could tell from the sound. I'm not surprised that it was low, since the car sat in the owners driveway for 10 years with no movement, so I would assume that its not unreasonable to think you would get some leakage over a 10 year period that would bring it into the bottom low of the gauge. I inspected everywhere and see no signs of leaks. After 2 days of charging the system is still holding, but like it was suggested, the valve probably didnt open to allow the gas into the compressor, but not exactly sure where a half a can of charge would have gone to???? Really don't know where to turn next, maybe its the compressor or maybe its a bunch of things. Is it worth buying the gauges and checking the high side? Meanwhile I'm going to turn my attention back to the interior work for now. This is turning into a bigger project than I expected.

Also, I've read a lot about a ground connection being a common problem, and that the high pressure sensor or all related sensors can fail if no ground is present. They describe it as being on a block I think near the service ports? But have not found any pictures of what we are talking about. Given nothing seems to be working, maybe its as simple as that. Can anyone elaborate?

U guys need to go back to the basics. Op jumped the relay and still a nogo on the compressor. What u do not see is a test to make sure there was 12v at the relay or even 12v at the compressor when jumped. It could simply be a fuse (or bad wire)? It could also be a bad clutch on the compressor if it does have 12v. Testing analog electric circuits is not hard. If u have continuity, voltage will travel from one side to the other. It just takes a little bit of time and a multimeter. If the op jumped the relay correctly it takes the control circuit out if the loop so it doesnt matter if any of the operating conditions have failed.

Quotes source post: 20084484

OK so here is what i've done. To test compressor I jumped 87 and 30. According to docs I found this should engage the compressor. Nothing happened. Then I checked for voltage on 87 and then on 30. It read .05 volts on either. And yes I tested the main 40 amp fuse. Not sure if I moved the ball, my electrical knowledge is very basic. compressor relay relay box behind back seats

Ok we r making progress. Pin 30 should ha e 12v at all time. Now we have to figure out why its dead. What year car do u have? Their may ne differences between the mk1 and 2 harness

Quotes source post: 20084752

2003 996 cab Thinking it may be related to improper ground. If you do not have proper ground, it basically shuts everything down from what I read. Just dont know where in the world that "terminal" block is located. could not find any pictures.

Quotes source post: 20084758

Nope not it. If u r testing pin 30 and the multimeter red leed is on pin 30 and the black leed is on ground, (assuming the battery is also hooked up) then pin 30 should have 12v. No other ground wire in the system effect this. If pin 30 has no power then a fuse or wire is broken. Give me a few and ill check the schematics and tell u what to test next.

Quotes source post: 20084790

Thanks for all your input. I did the test with the car running, just as you suggested, RED on pin 30 and black grounded on car. Just to be sure that I had the right pin for power, I did the same with 87. Results were identical.

You can buy a test probe to assist with your trouble shooting. Most can deliver 12v so you can test components.

new observation. I put the AC charging gauge on the low side again just to see what it read and it was at the bottom of LOW. WHAT??? But I dont see any signs of a leak. I charged it again to the Green zone, and nothing, so again, maybe multiple issues, since charging it should make the clutch kick in if that was the only issue. Now I'm afraid to put the dashboard back in, if there is a leak in the evaporator, I believe thats a remove the dashboard operation is it not? Is there any other explanation for this observation? I'm a big tough guy....but this is making me want to cry!

Gonna post a couple pics. One is of the front relay panel and the other is the ac schematic. The feed for the the ac compressor. Ill try to explain the cuircuit simply.... starting at the compressor and working backward. The gn/ye wire from the compressor goes ro the 87 pin on the ac relay, when u jump to pin 30 vt/ye, this goes to the pressure switch, (if closed) it continues to oit of the pressure sw as a bk/gy wire. This wire branches off but is fead by pin 87 of the heater relay (drivers footwell relay # 18) Lets start testing at the power for the relays come form 2 different fuses. Fuse c7 is an ignition on 7.5amp. This should read 12v on both sides with the key on. The 2nd is d6, 30amp always hot. This fuse should read 12v on both sides with the key in any position. If they r both good u need to jump or test relay 18. Pin 30 should be 12v if fuse d6 is good and if u jump it to pin 87.....that wire should make pin 30 on the ac relay(the one on the back shelf) hot and read 12v. Now u can jump and test for 12v at the compressor i would do this testing with tge key on and engjne off. U should be able to hear the clutch on the ac compressor "clank" if it energises. If u send power through the heater relay to the ac relay and pin 30 doesnt get power then then the pressure swtch is not closed (low refigerant) or its bad. U will need a refrigeration gauge to test. start with the easy first.....the fuses then move on to jumpers and let us know how the diagnlstic goes. It will narrow down the issue methodically so u dont waste time and money. Footwell relays Schematic Footwell fuses

Best way to charge low ac is to pump in nitrogen and add uv dye. With a blacklight u can find the issue

One other place to check, the power distribution block which is located on the firewall in the passenger footwell. Those are fusible links.

You guys gave me a lot of homework. Will go over it all and report back. THANKS!

I finally got around to purchasing a leak detector. The digital detector got a HUGE hit in the engine compartment near the compressor so I guess thats where the main leak is and from research its quite common. Also I got a hit coming out of the Air "handler box" by sticking down the main center vent with the fan running. Not sure if it was just sucking in AC gas from when I was charging the low side, and some of the residual is in that area, but since I had the dash out, I decided to pull the box out and put new AC evaporator in, because I NEVER want to have to do that again!!! Decided on a complete replacement of the box and AC evaporator kit $900 since the evaporator was at least 500$ for a decent one, and who knows what else might happen if I used the old one. Took me about 2 hours to get it out, most of the time was just trying to figure out what needed to be unbolted and where. Now that I've done it once, probably could do it in less than an hour. Not looking forward to putting it back in, its a tight fit and a lot of wiring that has to be routed correctly to make it fit. As you can see in the pictures, the foam issue is on full display. Another reason just to replace the entire box rather than fix all of it and hope it lasts. looks in great shape until you open it Foam is nearly completely gone. WHY did they use foam? Perhaps to always allow some air flow? No signs of leakage of AC or Rad fluid in the heater core, but will replace it out of an abundance of caution. this was the only piece of foam that was intact. Not exactly sure of the purpose but it is filthy.