A/C ECM/BCM Data

[DAVES89]

Checked the 1990 'vert's readings. I did the readings before starting the car. Car had not been driven in at least a week.

Vent temp is 48-52 degrees driving between 30-70 MPH. Outside temperature is 80 degrees. Low humidity.

The readings are;

ED04 - 21

ED23 - 24

BD21 - 21

BD25 - 26

BD26 - 25

BD27 - 24

BD28 - 23

BD32 - 28

I also cleared all the codes before I started. They were all history. However they were B122, B335, B336, B446. I was swapping clusters, Headlight switches, Stereos, Temp. Control so I expected the codes. I also added 1 can of R-12 freon some time ago, but never cleared the code. It did go to history, and when I took it out for a drive no warning lights came on.

[Guest Mc_Reatta]

Was car in garage or sitting outside when you took these?

Only odd reading is the coolant temp (ED04 + BD21) at 21 C. Hard to understand how engine could be 10 F under ambient at any time unless packed in ice.

The others average 24.5 C +/- 1.5 while the most correct one is BD25 at 26 C (80 F ambient).

Respectable numbers for 20 year old sensors I expect.

However, the low side reading (BD28) at 23 C (3 C low) says that the actual evaporator temp is limited by the BCM to be 3 C actual at its lowest point which is limited by the BCM to 0 C, or 37.4 F instead of 32 F.

So your being cheated out of 5.4 F which would give you a vent temp of 44.5 vs the 49 your getting in this oversimplified review.

Sounds like a challenge is here to come up with a table that you would input your BD28 reading into along with the ambient temp at rest, and it would give the value of a resistor to mount to the low temp sensor to compensate for any error in the sensor at reading 32 F so maximum performance could be restored.

[DAVES89]

Car was in the garage with the door open. Reading was taken about 1:20 PM Central Standard Time. I will take the readings again tomorrow AM when both cars will be cold.

I hope the challenge of making the table is to be done by you. I ain't got that kinda learnin...

[DAVES89]

OK Here is new readings;

1990 'vert

ED04 22

ED23 21

BD21 22

BD25 19

BD26 19

BD27 20

BD28 19

BD32 20

1989 Coupe

ED04 22

ED23 23

BD21 22

BD25 19

BD26 19

BD27 21

BD28 19

BD32 30

This is with both cars in the garage morning temperature about 50 degrees. They had not been run since 3:00 PM Sat. afternoon.

[drtidmore]

Here are my '89s readings.

Actual interior temperature at time of readings, 21.83 degrees C as measured several locations with my infrared thermometer.

Car had been sitting since 9:30pm last high (it was at full operating temps at that point).

ED04 - 23

ED23 - 22

BD21 - 23

BD25 - 23

BD26 - 22

BD27 - 22

BD28 - 21

BD32 - 39

Not sure what to make of the BD32, sun load temp reading. The sun is out and maybe it is reading the temp off the exposed roof over the Reatta. A shorted circuit would give a reading of 85 and an open circuit would be -34 (per FSM), so maybe I am fine. I think I will try this again in the morning well before sunrise and see what kind of BD32 reading I get.

I am pleased to see the critical AC low/high temp sensors being in close agreement with each other and with the ambient and coolant reading. As I had already measured my center outlet temps in the upper 30s, I pretty much knew that the low temp sensor must NOT be tricking the BCM into shutting off the compressor prematurely.

I tried to verify the low pressure sensor actual temp using my infrared thermometer with the AC running and the compressor cycling due to the cool ambient temps BUT the heat from the engine compartment was sufficient to raise the tubing temp directly around the sensor several degrees higher than the sensor itself was indicating. Since BD28 was SO close to all the others after sitting overnight, I am going to assume that all is well.

David T

Edited September 29, 2013 by drtidmore (see edit history)

[Guest Mc_Reatta]

Data looks pretty good as most readings within 3 C of each other ~ +/- 2.5 F.

David T, can't rely on that sun load reading (BD32) if car is outside in daylight.

Daves89, looks like that sun load sensor is going bad in your coupe unless there was some reason it would have been hotter than everything else. Looks like it was around 66F inside your garage at the time.

From these numbers, its hard to blame a low temp sensor for the air vent temps.

[DAVES89]

Thanks for that, but why am I only getting to 49 degrees at the vent?

[Guest Mc_Reatta]

Set your diagnostics up to monitor BD28 while you drive around. Because we have cycling clutch orifice tube based systems, getting extreme performance from the system is prevented. (I used to have a car that would blow snowflakes out of the vents)

In a properly working system, the BCM shuts the compressor off when the low temp sensor tells it the evaporator temp is -1C (30 F) and won't turn it back on till it rises to 9C (49F). So that means the system can be cycling back and forth between those two values which means the average temp of the inside of the evaporator is ~ 5C or 41F. If you monitor BD28 you will see it cycle between -2C reported up to ~ 10C as the temp overshoots a bit on each end. Now the vent temp will never reflect the core temp of the evaporator unless the cabin temp is also close to it, and if your cabin temp is in the 40s, I wonder why your still running the AC. :cool: So a vent temp of 49F is reasonable in under these conditions.

So are you stuck at this performance level? How can the braggers claim vent temps lower than this?

They, or their AC tech, understand that the secret to getting the best performance out of a CCOT based system is to fine tune the refrigerant charge level so that the low temp sensor never quite gets to -1C to shut the compressor off. If you can get the low temp to stay at 0 C all the time, you will get the best cooling effect from the evaporator that is possible. With long soaks and not too terribly hot ambient and cabin temps, a vent temp in the upper 30s should be theoretically possible, and their claims of low / mid 40s are believable.

So how do you get that low temp sensor reading to stay at 0 C all the time?

And the answer is.....(drum roll please)........ you can't. It's impossible! There are two many variables in the system too allow for it. Ambient temp and humidity, compressor speed, air flow over the condenser and evaporator, cabin temp and humidity, are changing all the time and influence that temp.

So do you throw in the towel and storm off to the car lot to find a new car? Probably not since you are suffering from Reattaitus.

So here's what you can do to get closer to this magic 0 C goal:

While system is apart for service:

Make sure all the old oil is removed or accounted for so that the oil charge level doesn't get too high when new oil is added.

Install a variable type orifice tube if you're game, as it can help to maintain the temp of the refrigerant in the evaporator by compensating somewhat for changes in the pressure changes at the orifice due to changes from compressor speed and high side temps, etc.

Changes you can do any time would be to get the coolant fans running at high speed all the time the AC is on, and if you're reprogramming the ECM, increase the idle speed while you're at it.

The last step is to tune the refrigerant charge to get the low temp to hover at 0 C for a selected set of conditions that represent your normal world situations as closely as possible.

The process is simple enough, as lowering the charge level slightly will decrease the low side temp, and increasing it slightly will increase it.

The standard practice to charge a system for the pros is to add a specific calculated weight of refrigerant and check performance. For us backyarders, we add cans to get the low pressure gauge up to 30 some psi and keep the clutch from cutting out constantly. When we do this, we are supposed to increase the air flow over the condenser and to raise the rpms to simulate the car driving down the road and then do the charging.

To fine tune your charge, pick a set of conditions that are typical for you, say ambient temp in upper 80s (maybe mid 90s) , fairly high humidity, air flow and engine rpm that simulate driving down the road at XX mph. If you have your fans running at high speed, you have air flow that should simulate speeds from stopped to 40 mph or so, so just pick a middle engine speed of the normal range of say 1500 rpm.

So at a time when the ambient temp is where you want it, hook up your charging equipment and start the car and the AC and run till the engine temp stabilizes and the AC has had time to stabilize also. Raise the rpm to your selected value, and hold it steady.

Monitor BD28 and see if it is reading a constant temp or it just cycles between -2 C and +10 C constantly.

If it reads a constant temp that is above 0 C, you're slightly overcharged, and you should bleed off a slight amount of charge from the system and let things settle a bit and recheck. You hopefully will now show a stable reading closer to 0 C. Repeat this process to walk the reading down to 0 C and you're done. Button things up and you are set to have maximum AC performance at the conditions you have selected.

If your BD28 readout is cycling, you're undercharged. So you need to add a little bit of refrigerant and let settle and recheck. Hopefully you'll see a slowing of the cycling rate of the system. Keep doing this until you get the cycling to stop and the system to read a steady 0 C or maybe even -1 C. If you over shoot, and get above 0 C steady reading, just bleed a little charge off.

Now as you observe what BD28 does as you adjust the engine rpms. When you let the engine fall back to idle speed, you will see the temp rise to above 0 C which says you're not achieving max performance anymore. Additionally, as you increase rpms above your target, you will see the temp fall below 0 C and the system go into cycling. So again, your not at max performance anymore. Also, if you look at BD28 at another time, when ambient conditions are hotter or colder and more or less humid than your set conditions, you will probably not be stable at 0 C even with the same airflow over the condenser and the same rpms as your used when charging. Such is life, and what makes charging an AC system as much of an art as it is a science.

[DAVES89]

Thanks Mike! I have downloaded this info and will save it for next summers heat wave. We may hit 80 tomorrow, but won't have the humidity so I will wait for next years heat/humidity.

But to be sure I heard you correctly I can do my reads with BD28 while I am driving. And "bleed off" any extra freon and use it as a guide to add if I am low?

[Guest Mc_Reatta]

Yes, I do it often when I'm not happy with my AC performance for any reason. Let's you know whats going on at that time under current conditions, and before a code is set.

I got in the habit when I was creating those fan cheater cables and seeing what difference they made.

Since I always seem to end up with half a can of R 134 left after charging a system, and since my equipment won't allow me to keep an open can for any length of time, I do a quick check of my other cars to see if they could use a shot before a low refrigerant code comes up, and before it goes to waste.

[DAVES89]

Today's temp was 78 degrees, however the humidity was very low. I had the A/C at max cool and drove it from 30 to 75 MPH. It would consistently read between 2-8 so that would mean I am slightly overcharged [This is on the Red]. However I think I will leave it until spring/summer next year in case I have any "leakage". Unless you think it is a bad idea to leave it over charged over the winter.

BTW these diagnostics are great. I will confess that I wasn't aware that I could get readings after I had started driving. For example I was in diagnostics on BD28 but the air was off. So I pulled over to the side of the road pressed the climate "hard" button, turned on the A/C, set my temperature, hit the status "hard" button and the ED28 page came back and I was all set.

These are really neat cars!

[Guest Mc_Reatta]

Yes, I'd just leave it alone till next summer. Wow a high of 78 degrees and low humidity. I've forgotten what that feels like. Maybe in another couple of months.

Say, while your roaming around Gibson's with some spare time, take a look at later model cars (96-?) for one that might have a high efficiency condenser that would fit into our Reattas and be able to hook up. 80s and 90s are the same overall size I think, but the size and position of the tube connections are different.

The main issue with using 134 in a R 12 system is the condenser is 10 % less efficient than it should be. Late model cars designed for 134 out of the box usually compensated for this by keeping the condensers the same size, but changing them over to incorporate micro-channel design to boost efficiency.

The downside to this is it makes them pretty much impossible to flush out, so they need to be replaced if debris gets into the system, as in the case of black death etc.

But if a suitable high efficiency replacement could be found, then we could probably achieve true R 12 performance with a converted system.

[DAVES89]

I would think a '93 Riv would have both the "right" size and be 134...

[Guest Mc_Reatta]

I would think a '93 Riv would have both the "right" size and be 134...

That might be too old to have incorporated micro channel design though.

Here's a sketch that shows the higher efficiency designs vs the old tube and fin design.

You can tell them apart by looking along the side edges for the tell-tale round tubes looping down.

[Guest Mc_Reatta]

Looks like the Riviera went to the high efficiency design in 95 on. Connectors have been moved to the bottom of the unit and look quite different from ours. Doubt that would prevent a hydraulic hose maker from coming up with adapters that could be used to connect them together.

Dave, if you can find one, check if the way it mounts to the car's radiator framework is radically different. They look much thinner front to back, but they should fit in the same space.

[Ronnie]

Can you tell if the ones in The Reatta Store are better than the ones that came on the Reattas?

[Guest Mc_Reatta]

Couldn't confirm by photos on Amazon, but side views I found on Autozone for them show them apparently to be old school tube and fin design.

[drtidmore]

As the current condenser attaches with couplings 6" or so away from the top of the condenser, it would NOT be all that difficult to make extension tubing to connect to the existing couplings (located at bottom of windshield washer fluid container) and travel down and connect up with the fittings located at the bottom of the new design. This assumes that mechanically the newer design would fit and or we could adapt to make it fit.

(update) went online and looked at the '95 Riviera condenser and two things I notice. It shows to be 2 inches wider and there is a unique connection on one of the fittings which would complicate creating a set of adapter/extentions tubes for our Reattas. I can't find a pic of what the unique fitting mates against.

David T.

Edited October 1, 2013 by drtidmore
more info (see edit history)

[DAVES89]

David T. try the '99 Buick Regal. That is a smaller car and still a Buick...

[drtidmore]

Oddly enough, even WIDER (almost 30" vs 27.5" on our Reattas) and STILL the old tube and fin design ('99 Regal that is). Looks like Buick held off putting the GOOD stuff on the lower priced cars for a few years after putting it on the Riviera. It does have the same strange connector (the one with what looks like a guide pin).

Pic from Autozone for '99 Buick Regal

David T.

[drtidmore]

Looking at various universal parallel flow condensers, I have found a 3 pass, unit that measures 16"X26" (Reatta 15.56"X27.5").

http://racewayparts.com/16x263passwbrktsparallelflowcondenser.aspx.

Note that the connections are at opposing corners so a new section of rigid tubing would have to be fabricated to go from the top connection, over the top of the condenser and then mate with the existing coupler from the old condenser. Likewise a section of rigid tubing would have to be made to connect with the lower connection similar to the tubing on our existing condenser.

This might be easier than trying to fit a later model Buick parallel flow condenser into the Reatta. Thoughts?

David T