[StigHelmer]

After I bought my C280, I evacuated the A/C system:

Left the vacuum on for 30 minutes, turned it off. Let it sit for 30 minutes longer to ensure no leaks in the system and gauges looked good holding vacuum. Charged it with 25 or so oz. of refrigerant and enjoyed super cold A/C for about a week and now it blows hot air.

So I repeated the process, this time with UV dye added, drove for a couple days, a couple hours each day and inspected the hoses, valves and compressor with a black light and only see dye around the low pressure shrader valve (where I just think it went in.)

Either related or not, my electric fan is always on when you start the car.

I'm going to change the A/C temperature sensor that is by the gas pedal but I think there is another temperature sensor near the front of the engine.

Any thoughts on either condition and whether they may be related?

Thanks!

 

[georgebuhr]

Do you have the climate control unit that will let you check for codes through the display? That is where I would start.

 

[StigHelmer]

Thanks George - I had totally forgotten about that, I'll run some diagnostics and see what I get.

 

[Patman1]

Run the diagnostics, see what it comes up with, and also check the sensor readings while the car is running, note everything done, it will help you diagnose the issue. The sensor near the gas pedal is the evaporator temp sensor, it can be changed easily, but you probably won't have to (its reading is #05 on the CCU). The refrigerant temperature sensor it at the receiver drier, but it cannot be replaced just like that, the refrigerant first has to be recovered, its reading is #08 on the CCU. Also, you can quickly determine if there is a leak in the system by looking at sensor reading #07, that's the high side pressure. If it's really low, then you've got a leak somewhere.

 

[StigHelmer]

Any help with readout interpretations would be appreciated:

01 In-Car Temperature Sensor with Aspirator Blower (B10/4) - "OPE"
02 Outside Temperature Sensor (B14) - "77 degrees" (accurate)
03 Heater Core Temperature Sensor (B10/1) - "OPE"
05 Evaporator Temperature Sensor (B10/6) - "CLO"
06 Engine Coolant Temperature Sensor (ECT) (B11/4) - "212" (wtf?)
07 Refrigerant Pressure in Bar : "CLO"
08 Refrigerant Temperature Sensor (B12/1) - "HI"
09 Not Used - "129" (if it not used why am I getting a value)
10 Blower Control Voltage - "175"
20 Control Current for Auxiliary Fan exp. : 7 = 7 mA = 04 degrees 0 (??)
21 Engine RPM. example 00..99 (x100) = 9900 - 240
22 Vehicle Speed - 050 (vehicle was stationary)
23 PIN 58D exp. 99.0 = 99% of Battery Voltage- 050
24 Battery Voltage : 12.8 = 12,8 Volt
40 A/C Controller Software Version Coding - NOT DISPLAYED
41 A/C Controller Hardware Version - NOT DISPLAYED
42 Variant code 1 - NOT DISPLAYED
43 Variant code 2 - NOT DISPLAYED
50 Not Used - 77
51 Not Used - 72
52 Not Used - 50 F degrees
54 ON/OFF A/C Compressor emergency off signal from engine control module. - OFF

DTCs were

226 In-Car Air Temperature Sensor (B10/4)
228 Heater Core Temperature Sensor (B10/1)
230 Evaporator Temperature Sensor (B10/6)
232 Refrigerant Pressure Sensor (B12)
233 Refrigerant Temperature Sensor (B12/1)
422 Serial Interface Connection (K1) to Instrument Cluster (IC)


My obvious questions are as follows:
1) What does open and closed mean on reading values?
2) How am I getting values for things that are not used ?
3) Is it actualyl possible that all five of those sensors are bad? Is there a central place they all go that could be the problem?

Any insight would be highly appreciated.

 

[Patman1]

I'm not sure exactly which of those sensors connect directly to the CCU. The engine coolant temperature sensor connects directly to the IC, which then sends the relevant data to the CCU via the K1 interface.

It' quite possible that all of those sensors are bad, they are more than 20 years old after all. The only expensive sensor in that list is the cabin temp sensor. Everything else is fairly cheap. However, there's also a slim chance that the CCU itself is bad. If you have access to a known good CCU, you could plug it in, code it to the car (there is a specific button sequence to code these), and see if some of the issues clear up. You could also start by replacing the evap temp sensor, it's the cheapest and probably the least hassle of them all to replace. If you get a real reading afterwards, it means you're on the right track and the CCU is probably fine. I say probably because I don't know why you're getting that K1 interface issue, you might have to dig deeper into that to solve it.

 

[StigHelmer]

Thanks Pat!

I changed the Evap temp sensor under the dash and the electric fan stopped going constantly! So there is half my problem.

I didn't take sensor measurements yet, but after clearing codes and driving for 2 hours, the only pending code is 451 - which I think is the diverter flap. If that is stuck, then maybe that's why it's hot.

When I turn on the car sometimes a loud THWAP comes from behind the glove box, always has since I owned the car. I've always assumed it was some port on the A/C (it makes that sound when you turn off the A/C unit too sometimes) but since initially didn't make the air not-blow-cold I ignored it.

 

[StigHelmer]

Actually - it was 421, not 451, pulse module - (apparently thanks to jack ass Teutone, I can't even edit my posts. )

 

[georgebuhr]

I am familiar with that THWAP. Mine did it for a long time too. Pulling the dash and replacing the bellows made the THWAP go away, but it was because one of them had a leak. I think it was the recirc door bellow. Cannot be accessed any other way unfortunately, but there is nothing terribly hard about pulling the dash if you are willing to tackle it, its just time consuming.

 

[StigHelmer]

After I saw that video I posted a while back of the Chinese guy do the evaporator core replacement I have been really nauseated by pulling the dash. Even though it is probably way easier and has way less room for error, I think I would rather replace my brake band on my transmission again if I had to - maybe once my backyard gets better I'll get the psychological willpower to pull it