2004 C70 AC and Cooling fan not engaging

Post by **hansenjg** » 17 Aug 2014, 08:32

Hi everyone. My wife said her A/C wasn't working. The clutch on the compressor was not pulling in. All the interior stuff works OK. Light for AC comes on, Fan comes on, etc.

I have tried the following:
1. Jumped out the AC relay and the clutch pulls in and the AC gets cold. Charge appears to be OK using one of those gauges from the auto parts store. Engine cooling fan DID NOT engage when I jumped the AC relay (should it?). I let it run like this too long I think, as it sounded like a high pressure relief valve opened. I quickly turned it off and told my wife "it's supposed to do that"

2. With the the car running and the AC set on max, I checked output at the 2 speed fan relay. No output to either speed. No input voltage to either input as well and I assume there should be. Swapped fan relay with the "parts car" with no change.
3. Jumped fan to 12V and it runs in both speeds quite nicely.
4. Verified against my 2003 XC70 that the cooling fan looks like it should come on whenever the car is calling for A/C, even if the compressor is not pulled in.
5. Checked fuses for A/C and Fan. Both OK.

So I am wondering what to look for next. I think my problem is that the cooling fan is not getting a run signal. Does the A/C compressor verify fan operation before it allows the clutch to pull in? Where does the "run signal" for the cooling fan come from? Anybody got an electrical diagram on this?

Post by **Ozark Lee** » 17 Aug 2014, 09:15

You can get the schematics from here:

http://www.volvowiringdiagrams.com/?dir=

If I'm not mistaken (and I may be) on your car the ECU controls both the AC compressor and the fan and it takes a scan tool like DICE to figure out the error.

...Lee

Post by **oragex** » 17 Aug 2014, 09:57

Maybe this can help. I run my car without the cooling fan assembly (the relay is shot). So basically, the whole cooling fan is out of the car. The A/C works as long as the car is moving, when the A/C radiator gets cooled enough.

Does your A/C blow cold air right after starting the car with a cold engine? If yes, it could be the A/C clutch plate that is disengaging when getting warm, common fault, fixable by adding small shims (look up on google).

Post by **hansenjg** » 17 Aug 2014, 13:15

Thanks.

Oragex, I am familiar with the bread clip fix as I did that on my parts car almost 10 years ago and it held the whole time. When I shunt the relay to engage the compressor it holds in just fine, so that's not it. It simply isn't trying to engage at all.

So, Lee, I guess it means a trip to the dealer? OUCH! I never let them do anything! I was afraid it might be the ECU that makes the decisions since all the hardware looks OK. I will drive it this week, take it to the dealer in Virginia Beach (where I work) and see what they say.

Post by **Ozark Lee** » 17 Aug 2014, 17:59

Scope out the schematics first just to make sure that the lines to the AC compressor indeed are triggered by the ECU. I've never touched anything that was made after 1999 so I could well be wrong about the control scheme.

...Lee

Post by **hansenjg** » 20 Aug 2014, 12:04

I looked over everything (thanks for the link) and it indeed does appear to be the ECU that tells the radiator fan to come on. I am quite certain my problem is the cooling fan input. Since I know all the individual parts are OK, I am taking it to my local mechanic who says he can read Volvo ECU stuff tomorrow. Said if he cannot diagnose it, he won't charge me. I will let you know what we find out!

Post by **hansenjg** » 21 Aug 2014, 20:28

Shop says it appears that the HVAC control unit is not sending the signal to the ECU to run the A/C. He suggests I take the control unit out of my parts car this weekend and test that analysis. Thanks DIA Automotive in Virginia Beach for respectfully discussing what you found and making this suggestion. I will report on how it goes over the weekend.

Post by **hansenjg** » 24 Aug 2014, 14:14

OK. Tried every trick in the book. It's fun and frustrating having a parts car.

But I swapped out the control unit, no change. Removed battery cable for over an hour to reset ECU, no change. Swapped out HP switch on A/C line, no change. Checked the LP switch and it seems fine (closed all the time). I will talk to my guy at DIA tomorrow and see what he suggests. Sure don't want to go to the dealer for this.

Post by **hansenjg** » 02 Sep 2014, 09:49

OK. It's fixed. I am the culprit on it taking this long and costing me some diagnosis money. Turns out to be the low pressure switch was bad. I replaced it with one of the parts car and it's fine. I thought I had checked it and told the shop I had, so they didn't look at it until I brought it in the second time. I think what happened was I bypassed the A/C compressor relay and it ran, so I figured the low pressure switch was OK. I was wrong. Very embarrassed by this.

The guy at the shop told me he called Volvo and they said it was $150+ and would take 5 weeks to get! They apparently rarely go bad. Fortunately the parts car came to the rescue.

Post by **scot850** » 02 Sep 2014, 12:02

Heck, if I had to admit to every mistake I have made 'learning' to fix cars, there probably wouldn't be enough time to do so. Next perfect human I meet will be the first...! Good for you to own up, but as they say, you won't make that error if there is a next time.

Neil.