1998 S70 A/C Compressor won't kick in on its own

TripWyre79 · Post by **TripWyre79** » 11 Apr 2015, 18:29

Hey guys, I am new the the MVS forum and wanted to reach out for assistance on this A/C issue as I am going crazy trying to figure out what the issue is and in NC the temp is already an average of 80 degrees and its only the beginning of spring. Okay, a little background information. The A/C worked amazing well 2 summers ago, but last summer it stopped and it was brutal, I'm not aiming to repeat last years sweat-fest again. I have read a good deal of past topics on the issue and those have given me a lot of information and places to start testing, but I still can't figure it out.

Here is the testing I have performed thus far.

My 1st step was to check all of the fuses. I found the A/C fuse in the engine fuse-box was burned out so I replaced it. The #5 to 10 amp fuse to relay system. Then I checked the A/C relay. I'm not exactly sure how to fully test it so I just jumped the relay. This caused the compressor clutch to pull in and start spinning, I was excited. However I used an A/C fill gauge to test the pressure in the system with the compressor on and it was about 10 psi.I filled it with R-134a until it hit about 40 psi.With compressor off the pressure reads about 90 psi, and its about 75 degrees outside. With the relay jumped and the compressor working, I started to feel cooler air from the cabin vents. All cabin fans and electronics have always appeared to work, A/C button depressed with solid green light, fan speed at all switch settings.

On the relay I tested voltage, between 3 and 5 I get 12v, between 3 and 2 i get about 0.57v. Between 3 and 1 I get about 0.04v. Between 5 and 2 I get 12v, between 5 and I also get 12v and of course between 5 and 3 I get 12v.

Next I tested voltage to the Low pressure switch harness. Between pins 1 and 2 I get 12v, I then tested both pins from ground, on pin 1 to ground I get 12v, but on pin 2 to ground I only get 0.02v. Next on the Low Pressure harness I tested Ohm value between both pins and got no reading, but between the switch itself it shows open at 0.00.

Next I tested voltage on the High Pressure sensor harness. With ground in pin 1 I tested pins 2 and 3 both showing approx 5v. Then I tested Ohms value between the pins. With Pins 1 and 2 I get a reading of 6.58 and between pins 1 and 3 I get a high reading of 57.00, Which I thought was strange but I don't know enough about the A/C system to know what it should be.

I then reconnected the normal A/C compressor relay and tried jumping the LP Switch thinking the refrigerant level might still be low. Jumping the LP switch did not engage the compressor clutch. with the relay in I get all the same voltage readings as above.

With the normal relay in, I tested the HP sensor harness Ohm value again. Strangely when I tested I believe between 1 and 2 the radiator fan kicks on every time but doesn't do that with 1 to 3.

Next I again jumped the relay between 3 and 5 and compressor kicked in, colder air from cabin vents, however, after a few moments of running the radiator fan kicks in and the pressure drops from about 40 down to around 20, when that happens the air from the cabin vents starts blowing warm until the fan turns off, the pressure rises back to around 40 psi. Then the air temp gets progressively cooler again. That is until the fan kicks on again and the process repeats itself over and over at about 1 minutes intervals. 1 minute with fan on and warm air and 1 mins with fan off and progressively cooler air.

I am now at an impasse with this issue now and don't know where to go from here. All previous topics on this showed me what to test, now I just need advise as to how to proceed from here. Any and all advise is appreciated.

Trip

P.S. Here is a link to YouTube of the video I made of the pressure cycling in reference to the radiator fan coming on and turning off.

Thanks guys

Post by **Ozark Lee** » 11 Apr 2015, 20:21

It behaves like it is still low on R-134A but it also also acts like the compressor is having a hard time. I can't tell from the video exactly what the compressor itself is doing so that is one piece of the puzzle that isn't completely clear.

How long had the car been running when you shot the video? How was the temp gauge behaving?

The fan should kick on as soon as the high pressure builds enough for the A/C to be functioning. In your case it acts like the high pressure sensor isn't telling the ECU to turn on the fan and the engine temp finally tells the ECU to do it and it draws air across the condenser coil and the system pressure drops. You can't really monitor the high pressure since there is no high pressure port on your car.

There are a few things that can cause high pressure side problems like a blockage in the system, usually from a blocked orifice tube or a bad accumulator/filter/dryer. It could also be a problem with the high pressure switch itself or it could be that there is air in the system. Did you pull a vacuum on the system before your recharged it? If you did have positive pressure like you indicated (although 10psi is barely positive) you shouldn't necessarily need to pull a vacuum but who knows what the overall history is.

In the video you show the pressure at around 25 psi and climbing until the fan kicks on, as that is happening is the compressor actually engaged and is the center of the compressor turning at the same speed as the pulley?

...Lee

TripWyre79 · Post by **TripWyre79** » 11 Apr 2015, 21:14

Thank you for your quick response, Ill try to answer all of your questions.

You cant see it very well in the video but the compressor is on 100% of the time, but that was due to the relay being jumped. It was jumped for almost all of my testing that I had done before.

When I shot the video, the car had been running for approx 40 minutes. I checked the temp gauge throughout my testing to make sure the extra load wasn't causing a temp spike. The temperature stayed static at what it always is without the A/C load, so there were no heat spikes.

With the HP sensor, is the ECU supposed to tell the fan to be on all the time? And when the fan is on (in a fully charge system) what is the lowest the pressure should go? Should it stay in the green zone even with the fan on or is it normal to drop that low, for instance, is the pressure value with the fan on what should be measured for determining if the system is low?

With the relay being jumped, and having these results, I'm wondering if any of these symptoms point back to the cause of the compressor not engaging with the normal relay in. The only way I've been able to get the compressor to engage is by jumping that relay, other than that it never engages.

I tried the Shim process last year during troubleshooting, but it never engaged then either. So far only jumping it manually has made it pull in. If the pressure is still low, wouldn't jumping the LP switch engage the compressor while using the relay in place. I had thought that but it didn't work.

Also, when I first engaged the compressor, there was a little over 10 psi, so I just filled it with the remainder of the can which brought it up to the 40ish range. I didn't vacuum the system though.

TripWyre79 · Post by **TripWyre79** » 11 Apr 2015, 21:29

Also, should there be continuity between the pins on the LP switch connector? When I put my multimeter on it on Ohm, I didn't get a reading between the pins,(With or without the relay jumped) but I did get an open reading of 0.00 on the physical switch connected to the line going into the firewall.

Post by **Ozark Lee** » 11 Apr 2015, 22:51

The way the ECU is programmed the A/C high pressure switch turns the radiator fan on high speed, full time, regardless of actual engine temperature. The low pressure switch cuts the compressor off in the high 20 PSI range - typically around 27 or 28 PSI and with a properly charged system the pressures should stay above that. Ambient temperatures play a big part of the system pressures but upper 30 PSI to lower 40 PSI low side pressures are more or less typical.

Given the way the low side pressures climbed I am guessing that the high side pressures were climbing as well and that the high pressure switch is likely your problem. If you can get the fan operating properly with the high pressure kicking it on then you can add R-134A until the low side pressure is maintained. Until you get the fan operating correctly you are chasing your tail trying to properly charge the system.

It sounds like the fan was running on high speed in the video but that is another thing that is hard to tell just by sound. To test the fan relay unplug the center connector with the yellow wire and the yellow/white wire. Ground each of the terminals on the relay, one at a time, and verify that the fan comes on at both low speed and high speed. That will verify that the fan relay and the fan are both operating as they should.

...Lee

TripWyre79 · Post by **TripWyre79** » 12 Apr 2015, 01:01

Okay, I used a light tester grounded on the negative terminal of the battery to each terminal and the fan came on at both low and high speed respectively, so it sounds like the high pressure sensor is not telling the fan to turn on, which would in turn drop the pressure showing the true range that the AC has charged, from my test earlier, every time the high-speed fan came on, the pressure dropped to the 20 range, so if the high speeds fan was on the entire time the AC was on, it would show me the true pressure point in the system. That would tell the ECU that there is enough pressure in the system to engage the clutch, right? So essentially my issue is the high pressure sensor is not telling the full speed fan to turn on when the AC is activated, and also that I still am low on Freon? Does that sound right? If so how do I proceed, and once those two issues are resolved, will the AC turn on normally using the compressor clutch relay? Without having to jump it?

TripWyre79 · Post by **TripWyre79** » 12 Apr 2015, 01:03

Also, aside from when the engine Temp sensor made the high-speed fan turn on in the video, the fan doesn't turn on on it's own with just the A/C compressor engaged.

Post by **abscate** » 12 Apr 2015, 04:19

Making inferences from these pressure measurements is very difficult.

Scan for some good posts my jimmy57 on measuring an equilibrated AC system to correctly determine charge. Many people have messed up their AC by putting too much charge in thinking more a freon is better cooling, which is false.

You really should evacuate your AC too, since you know it lost charge. Humidity that leaks in will quickly kill your compressor. Evacuate, replace dryer, PAG oil.

Did you find the source of the leak? The evaporator core on these cars usually won't last 17 years...that's a 100 USd part, 10 hour labour of love

Post by **Ozark Lee** » 12 Apr 2015, 09:30

TripWyre79 wrote:Also, aside from when the engine Temp sensor made the high-speed fan turn on in the video, the fan doesn't turn on on it's own with just the A/C compressor engaged.

The fan should turn on provided that the high side pressure is going into its operating range. I'm not certain what that high side pressure actually is and it is a moot point anyway since there is no high side test port. Just turning on the compressor doesn't turn on the fan.

I think I have a handle on where you are at this point:

The fan and fan relay are both operating.

The wiring to the fan relay from the ECU is good since engine temp will trigger the fan

The compressor appears to be working.

The R-134A charge is low as seen by how low the low side pressure drops.

The low pressure switch may or may not be good, we don't know since it is bypassed. Chances are it works fine. That switch gets changed much more often than it should and I have never, ever, seen one that is actually bad.

At this point, were it my car, I would scare up a high pressure switch at a junk yard. I have had a high pressure switch go bad on one of the cars but it was my fault. The way it sticks out there I was removing something else, the wrench slipped, and I broke it in two. I think it was a $3.00 or $4.00 item at the "You Pull" yard. With your existing charge, after you replace the switch you could then verify that the fan comes on as your low side pressure drops.

Were it me I would then recover the R-134A (I actually have a recovery machine), replace the accumulator/filter/drier, and pull a good vacuum (under -28 psi if that is the only way you have to measure it) and let set for an hour or so and see if the vacuum holds. The best way to measure the vacuum is with a micron gauge and get it under 500 microns but that isn't something that most people have around. Since I service the HVAC systems at rental property myself I have purchased all of the fancy gear.

If the vacuum holds then I would add refrigerant. I buy R-134A in 30 lb jugs and I have a refrigerant scale so I can actually weigh it in but it you can do it with your gauge and the small cans and get close enough. You can try to add a can with the stop leak stuff in it and it won't hurt anything, it usually doesn't help either but it has really slowed down a couple of my leaks at the compressor shaft seals.

...Lee

TripWyre79 · Post by **TripWyre79** » 13 Apr 2015, 15:12

Okay, I'll see if I can get one from pull-a-part this weekend and test it out. If I may encroach on your knowledge a bit more. The car has had a couple other little things i had wanted to ask about. The first being the alternator. I've noticed as the car is running for long periods of time it starts putting out less and less voltage. Starts at around 13.7 v and by the end of my trip to work. It's at around 12.7. If I need things like headlights and windshield wipers it's even lower usually sits at around 12.4 12.3 V until the following day when I turn it on and it starts back up at 13.7 V. I know that's low in the first place, I think I heard somewhere that the alternator voltage shouldn't be below 14 volts. Addition to that whenever I coldstart my car, it idles pretty poorly, sometimes so low it acts like it's about to stall and has stalled on occasion, but after about 5 to 10 minutes of driving it idles perfectly normal. And last but not least the seat heater only seems to work when I first turn the car on and will only stay on for about 7 to 10 minutes and then turn itself off even with the switch still activated, and then won't work again until the car has cooled down being turned off for a while. Any ideas on where to start looking on some of these issues, any advice would be greatly appreciated and thank you for your help so far.