Evaporator Temperature Regulator

[Davidov]

Foreword: This regulator has been discussed before, but no real answers.

I was having issues with my compressor "short cycling". It would only receive the 12V ON signal momentarily for about 2 seconds.

The pressure sensors (dual sensor setup), were receiving the 12V signal momentarily, so I followed it backwards in the system. According to the BMW ETM (old paper edition), and found the Evaporator Temperature Regulator.
I jumped the 12V signal from the A/C snowflake button, to the output of the regulator/relay and the A/C WORKS! :D

Now to solve the problem:
The ETM shows "early production" and "late production". Early production cars didn't use this regulator, only the evaporator temperature switch. (opens to prevent evaporator icing)

1) This part new is too expensive and hard to find. Anyone got a used one?

2)I wanted to find another 6-pin relay to wire in, but the regulator has some sort of circuit board with processor chips, probably for temperature control.

3)Can I bypass the regulator completely? Since the old cars used only the sensor?

[Davidov]

Wow no replies. I'm going to bypass it with a jumper wire. I don't think anything will fry.

[jlevie]

I'd think you could replace that part with the early evaporator temperature switch. Simply wiring around it would work and if the system is converted to R134a there is very little risk of the evaporator going below freezing in temps where you'd want to have A/C on.

[Davidov]

I was thinking this as well jlevie.
My system does have an evaporator temp switch, that inputs to this Evaporator Temperature Regulator.
Wiring colors are a little different from year-to-year, but it is still accomplishing the same task.

110F degree days in Texas, I don't see ice forming on much of anything. :)

[Davidov]

I was wrong!

The high pressure sensor returns a signal to the ETR.
So I am converting the dual refrigerant pressure switch system to the updated single sensor/switch.

[kjlinden87]

Where is it?

Does anyone know where the Evaporative Temperature Regulator is located in a 1987 325es? The Bentley Manual isn't very helpful and for some reason and can't see any pictures on this forum. I'm hoping I can get to it without removing the dash. A general description would be great. I want to jumper it to see if it is causing my AC problems.

Currently I'm not getting power to my compressor but both of my high and low pressure switches show continuity. I want to jumper 3, 5.

[Das Delfin]

take out the lower steering column cover and stick a flashlight up near the heater box. Look behind the footwell vent. The evap reg is the black relay looking thing tucked up behind there with a metal clip on top. You have to really get your head in there. Twist the bottom toward you (the bottom being the long end) and it should come out. Then unplug it from its harness.

are you getting 12v to your low pressure switch? (with the car on, motor running, snowflake pressed and lit up blue) If you are then your evap reg is likely good. If not eeuroparts has them for like $40

I pretty much just did a mini write up of this

[kjlinden87]

Thanks, I think I found it. I'll try to jumper it this weekend. I don't have 12V to the low pressure switch but I do have power to the switch and the switch is working.

[Economy Sport]

I read somewhere else as well that "early models" don't have the evaporative temperature regulator, which explains why I couldn't find one on my January '86 model during an extensive search. And sure enough, the 1986-specific ETM shows a *evaporator temp switch* instead. Trying to locate this should be fun. In the meantime, during a recent heat wave, I ran a wire from the fuse box through the high pressure switch to the compressor. It's pretty ghetto but it works. ;-) Even at idle with no auxiliary fan I'm getting 38-44° at the vent, depending on the blower speed. Edit: I should mention that "heat wave" in the San Francisco Bay Area really isn't saying much, LOL. But I'm getting vent temps at least 40° colder than the ambiant outside temperatures. Yay for R12!

[Das Delfin]

^ Yeah yours in particular had a simpler setup. Unfortunately I can't help you in your search, but if its any consolation I had to stick my head up under the dash with a flashlight before I found the relay I was looking for.

The main change was that the newer relays also had a loop back from the compressor to adjust for engine idle speed. Ie it was a different way to send a signal to the computer to up the idle when the A/C was on. But they both returned a reading from the A/C evaporator temp sensor to make sure the evaporator didn't freeze over

[jeffnhiscars]

The ETR is set for 37 degrees so vent temps would have to be high 30s low 40s for it to trigger (not easy to achieve). If it doesn't trigger, the evaporator ices up, it stops cooling, temps rise, you do something else, the ice melts, the ETR closes and life goes on. Home ACs and fridges freeze up all the time and I'm not aware of permanent damage ever occurring although I suspect if the compressor kept running it wouldn't be too happy for long.

The temp differential between ambient and the vents is really the most telling gauge of how well the system is working. Houses have closes systems and they look for 17-18 degrees since it's Recirculating air and of course houses are far better sealed and insulated than cars.

BMW says our cars should have 20-21 differentials (converted or not) so 40 is great. Being anal about my ac (in case anyone hadnt noticed) I keep an IR gun handy and have been getting 42 on my converted system (avg humidity, 2500rpms on open roads). It's great when it's 95 outside and you are freezing in your Cabrio and have to turn the fan down to 2 :)