A/C problem (c280)...please advise

[jlulu]

The Sacramento heat is just around the corner and I just discovered that my A/C isn't working in my 1998 c280 - the A/C blows only outside air temperature. My unqualified guess is the compressor isn't engaging. I've ready a bunch of posts, but I'm not sure what my next step is.

Using the information in this post I've used the A/C Diagnostic display to gather data.

Reading the PBU codes I get: d1 *A (or dl A)

And here are the "REST" Button results (I took these results with the engine on):
1 94*F
2 92
3 80
5 91
6 19 5
7 26*7
8 174
9 35*F
10 580
20 10*0
21 060
22 000
23 000
24 13.8
40 03
41 03
42 02
43 6-C
50 84*F
51 LO
52 37*F
54 OFF

What does "d1 A" mean? Does "000" for 22 mean the compressor is not engaging?

Any help is greatly appreciated…

[jlulu]

I just found a bad connection to the compressor. Now the A/C is blowing about 61*F. Better, yet still not good.

Should I try recharging it (is it simple enough to do myself)?

[Ali Al-Chalabi]

If you know how to recharge an A/C system, it is simple enough.

Is 61F the output temp at the vents?

[jlulu]

61*F is from the #3 "REST" Button (I'm assuming that's what it means). Am I correct?

[Matt L]

Originally Posted by jlulu

7 26*7

If this is the high-side pressure sensor reading, it may be the problem. That's way too high unless the system is under an extremely high load. From your post, it appeared that the compressor was off.

[forp]

A couple of things. If your EC light is on try pushing it for about 30 seconds. If it goes out then your AC may be back at least temporarily. Also, pull the plug to the pressure sensor at the drier. Its the aluminum canister down near the left headlight. Pull the connector with three wires. One is ground, one is the sensor output, the third is the 5V bias. With the ignition on, check them with a volt meter. If one is more than 5V then the problem is in the climate control module 5V bias regulator. The high bias is causing the pressure sensor to erroneously report a high pressure condition. I don't remember the wire color codes. Just look for a wire with high voltage. If the pressure sensor bias is too high it is actually fairly easy to repair the CCM and make it right.
Dan

[jlulu]

I'm not having a problem with the EC light staying on. As Dan suggested I tested the pressure sensor at the drier - it read ~1.75V (well below the 5V warning level he suggested).

Also, I tested the refrigerant level...per my reading I got 45 PSI right on the top edge of full - almost too high. To my knowledge the system has never been recharged.

I can hear the comressor turn on...yet it's taking a long time to cool and when it does the air temp is only at 61*F.

Any other suggestions?

[forp]

"One is ground, one is the sensor output, the third is the 5V bias"

Of the three wires, one should be a constant 5V +/- very little. If the most you see is 1.75V then the +5V bias to the pressure sensor is not right.
Dan

[jlulu]

Dan, I see that you fixed your problem with a pressure sensor (reading old posts), but I'm not finding a post that describes how. Can you outline the basic steps for me?

[forp]

I repaired a specific problem, the pressure sensor bias coming from the climate control module(CCM) was too high. The fix for this involves opening the CCM and replacing a component. Not too bad if you have the soldering tools, otherwise an audio repair shop could to it for you. I'LL post more details on this if you need them. However, if the bias level is too low, you may have other problems. Either way, one quick fix is to cut the wire near the sensor and supply a 5V bias from a homemade regulator harness. This will get the sensor bias back to where it should be and give you the use of the AC while you try to find the root cause of the problem (probably a faulty CCM). I fixed mine this way and used it for quite a while before actually going into the CCM and finding/repairing the problem(a faulty 5V regulator). As I said, the bias should be 5V +/- very little. If you are sure the bias voltage to the pressure sensor is causing problems, I can provide more details on how to put together a 5V regulator harness. With basic soldering capabilities and parts from local auto parts/electronics stores, it's pretty easy to do.
Good Luck, Dan