My A/C blows pretty cool

[DAVES89]

I did a lot of housekeeping on my A/C system. I cleaned the radiator and condensor, removed the blower and the blower control module so I could clean inside the plenum. I got out lots of gunk and the air volume is really good. However I do not get the "ice cold" air out of my vents. It blows "pretty cool". The outside temperature is about 75 degrees.

 I cannot find my therometer so can't give a vent temperature.

 My BD28 readings at 60 MPH are -2 to 9 and then it cycles back down to -2 and repeats. Stopped in traffic it reads 2 sometimes 3.  After driving the car and parking it there is no "puddle" of water under the car either at idle or off.

 Any ideas?

[Guest Corvanti]

the first thing i'd do is beg, borrow or buy at least a low pressure gauge to check the coolant pressure level. is it R-12 or R-134-a? if 134, it's a easy DIY if she needs coolant.

 

if it's one of the 89's, make sure the CRT is showing "Max Cool" for testing.

[DAVES89]

It's R-12 on the Red 1989. According to Mc_Reatta [where is he!?!] the reason for going to diagnostics on the CRT is that gives you the pressure. That's why I read the BD28 it reads the cycles.

 We are leaving soon for what my grandaughter call "the Camper House". I can read it on the way. 

[Ronnie]

 

My BD28 readings at 60 MPH are -2 to 9 and then it cycles back down to -2 and repeats. Stopped in traffic it reads 2 sometimes 3.  After driving the car and parking it there is no "puddle" of water under the car either at idle or off.

 

You really need to check the temperature of air coming out the vent to know how well the AC is working. BD28 is telling you the temperature (Celsius) of the freon as it goes into the evaporator just before the air crosses it. Your numbers indicate the AC should be working correctly and you should be getting really cold air coming out the vents. However, if you remember my past experience with my car's AC the Low Temp Sensor can be sending an inaccurate reading (BD28) to the BCM. The BCM displays on the CRT what the Low Temp Sensor is telling it.  Even though the BCM is seeing -2 from the sensor (which is slightly below freezing) when it kicks the compressor out, the actual temperature when the compressor kicks out could be higher. When you get home and have time I can tell you how to determine if the Low Temp Sensor is keeping the compressor from running long enough to cool the air down.

 

As far as a water puddle... The amount of humidity in the air makes a difference in how much water will be produced. 

[padgett]

Also need BD27. A partly clogged oriface screen will send the HI side up while the LO side stays low. Using the LO side only just works if you have a good system that may be a little low on freon. Just adding freon trying to brig the LO side up when it isn't low can make things go bang.

[DAVES89]

OK I have been back and ran all the tests I think we may need.

 Vent temp is 60 degrees at idle, 35 MPH and 65 MPH

 Idle

 BD21 93

 BD22 4

 BD23 17

 BD24 0

 BD25 32

 BD26 38

 BD 27 45-52

 BD 28 3

 

 35 MPH

 BD21 92

 BD22 4

 BD23 17

 BD24 0

 BD25 29

 BD 26 27

 BD27 30-32

 BD28 -2 to 9

 

65MPH

 BD 21 92

 BD22 4

 BD23 17

 BD24 0

 BD25 27/28

 BD26 27

 BD27 28/29

 BD28 -2 to 9

 In case you want my cold readings [i ran these about 2 weeks ago before starting the car] here they are;

 ED04 23

 ED23 22

 BD21 23

 BD23 17

 BD24 0

 BD25 22

 BD26 21

 BD27 23

 BD28 21

 BD32 39

 

 Ronnie I am interested in how to check the low temp sensor.

 Thanks in advance!

Edited May 25, 2015 by DAVES89 (see edit history)

[Ronnie]

Dave, Based on Padgett's previous post, the test I had in mind might possibly damage your AC system. It would keep your compressor from kicking out so you could see if the vent temperature goes down without the compressor cycling. I admit I'm no expert on the AC system and I wouldn't want to suggest you do anything that might cause a problem.

[Ronnie]

Your 60 degree vent temp isn't too good. I just checked and mine will go down to the low 40s on a thermometer stuck in the vent on the right of the Instrument panel.

[DAVES89]

I am going to read up on what I need to do. I really think I have a sensor issue like you do Ronnie. I believe what you did was put a "jumper" on the sensor lead to bypass the sensor to make the compressor run. Then read the vent temp. It should be in the low 40's

 This will tell me if my freon levels are good. Then I can check the resistance at the sensor. If that is incorrect with the manual I can install a resistor to "fool" the sensor. I can get more sensors from the local You Pick, but to install different sensors would allow the existing freon to escape. Then I should just consider going to r134. Freon is much cheaper. 

[harry yarnell]

I thought the low side sensor was just a switch.

Also I THINK you can unscrew the low side sensor (switch) without loosing any Freon; like it's a Shrader fitting. Don't hold me to that...

[Ronnie]

I thought the low side sensor was just a switch.

Also I THINK you can unscrew the low side sensor (switch) without loosing any Freon; like it's a Shrader fitting. Don't hold me to that...

All that is correct for the Low (Side) Pressure Switch. It kicks out the compressor when the freon pressure is too low. If the BCM sees the Low Pressure Switch is made for an extended period it will lock out the compressor from further operation until the BCM is reset.

 

There is also a Low Side Temperature Sensor in the low pressure line. It is a variable resistor that changes resistance as the temperature of the freon at the evaporator changes. The BCM uses the information from that sensor to cycle the compressor off and on to keep the evaporator from freezing up and to maintain the temperature you have selected. To my knowledge that sensor screws straight in to a fitting on the line and doesn't have a Schrader valve that would allow you to change it out without losing freon.

 

The low pressure switch is still available new. I can't find a source for new low temperature sensors. If we are going to keep our Reatta AC systems working we are going to have to find a suitable replacement for them.

[DAVES89]

I am reading pages 1C-30 and 1C-31 and I appear to be a "bit" warm with a vent temperature of 60 degrees [it should be 52Degrees +-2]. According to the book if my BD26 reading is 27 degrees my vent temp should be 52 degrees. I was at 60 degrees. But according to Chart 9 located on 1C-31, I must use gauges and compare the results of the gauges with the BCM readings. I don't have gauges.

 Any recomendations?

[Ronnie]

I am going to read up on what I need to do. I really think I have a sensor issue like you do Ronnie. I believe what you did was put a "jumper" on the sensor lead to bypass the sensor to make the compressor run. Then read the vent temp. It should be in the low 40's

 This will tell me if my freon levels are good. Then I can check the resistance at the sensor. If that is incorrect with the manual I can install a resistor to "fool" the sensor. I can get more sensors from the local You Pick, but to install different sensors would allow the existing freon to escape. Then I should just consider going to r134. Freon is much cheaper. 

 

Here is something you should check... Drive down the road with the AC running at MAX COOL and the diagnostics screen in BCM mode. Watch the triangles for LO PRESS and COMP. If you see the LO PRESS triangle flicker any you may need to have some freon added. If you see the COMP cycling on and off, the BCM a signal from the Low Temp Sensor that the evaporator is getting cold enough (about -2c) so it cycles the compressor off. If you have a thermometer in the vent and it is reading 60* the Low Temp Sensor is probably not accurately sensing the temperature. That is the problem I have with my bad Low Temp Sensor.

 

If I remember correctly, putting a straight wire across the low temperature sensor pins to jump it will result in the BCM setting a code because it thinks the sensor is too far out of range. I can't remember if that will kick out the compressor or allow it to run continuously with a jumper in place. It has been a long time ago when I did that.

 

You might have to use a resistor of the correct value as a jumper to keep the compressor running all the time. If you measure the resistance of your Low Temp Sensor in the morning before starting the car, a resistor of that value should keep the compressor engaged all the time. That is what I was going to suggest you do in my earlier post but Padgett's warning about things going bang steered me away from it. Maybe someone smarter that I can suggest a better way. Padgett may have some ideas or Mc_Reatta?

[Ronnie]

Dave, I hadn't looked at those charts before. According to them I probably have my AC vents getting too cold. I don't know if that will hurt anything. I don't have a problem with the evaporator freezing up that I an tell.  I'm pretty sure my vent temp was down in the mid to low 40s last time I checked it. I don't know what the BD26 reading was. I will try to measure the temps again today of it stops drizzling rain.

[DAVES89]

I went out again and looked at the arm behind the glove box. Years ago I had to fashion a "fix" on the clip on the left side of the arm that opens the door. This time I had extra clips so did a repair and it is back to like new. I once again put the therometer in the center vents and set it for max cool and read the codes. This time I got down to 52 degrees at the vent with at an outside temp of 27  humid degrees. According to the chart this is right where I am supposed to be. 

 My mechanic friend told me last year that he thought the Reatta was like some of the other luxury cars made that do not allow the vent temp to get too cold. 

 52 degrees isn't "ice cold" but now that I have very good air flow out of my vents it is pretty comfortable. I will be out running errands and will take my thermometer along and read temps all day. [And also codes].

[Ronnie]

I'm happy to hear you found the problem and got if fixed without having to change the sensor.

 

I just got back from checking my vent temp. With the CRT and my handheld thermometer showing the outside air temp at 81 my vent temp was 42. It almost feels ice cold on my knuckles while holding on to the steering wheel near the vent. It got that cold driving a constant 45 mph.  According to the chart that's too cold but it sure cools the car down good. I'm afraid the evaporator might freeze up on high humidity days if I drive for an extended period of time at a constant speed.

 

I could probably raise the vent temp a little by changing the jumper resistor but I think I will leave it as is until I can get another Low Temp Sensor installed that I know works correctly.

 

Don't let anyone tell you that 134a doesn't cool as well as R12.

 

[Guest Corvanti]

idk, i suppose i'm just too "old school".    the first thing i'd check is the low pressure fitting with a R-12 gauge (and probably the high also). since R-12 gauges are now somewhat rare - unless one can be found on ebay, etc. - and hard to find R-12 coolant to purchase for home garage use if needed (kinda a gray area in legality) - i'd take her to a trusted mechanic with R-12 gauges. if low, freon with leak detector could be added and be done with it - if no leaks found or other part failures found.

 

R-12 used to run around 40ish degrees. R-134a around 45ish. i really can't recall if my '89 had a "re-circ" option (inside air) when cooled down, or just bring in outside air to cool down.

 

don't "hurt" me too much for trusting this method over what the 'puter(s) have to say!!!

[DAVES89]

Here is the latest. I went on line last night and bought a r-12/r134 A/C kit. But it turns out after reading the repair manual yet one more time, I now have "ice cold" air. I kept looking at my readings and based on comparisons with what the repair manual says and what others told me, I kept thinking there can't be a problem, what was I overlooking? So I reread the manual about the rod adjustment for the vent door behind the glove box. It turns out that I was way wrong on my adjustment and what I was doing was blending warm air in with my A/C air. So after driving the car to an appointment, I started the car, left it in park and raised the idle to 2000 RPM's at "Max Cooling". My vent temp went right down to 40 degrees just like what Ronnie took a picture of.

 I drove home about 90 miles and the car was just perfect with the CRT set at 76 degrees with the fan running on low.

 So I can honestly say that after cleaning the radiator, condensor, and plenum for the blower motor, plus adjusting the air mix rod I have all the cold air I need.

 So it looks like I am in need of a good recipe for "Humble Pie".

[Ronnie]

Dave are these instructions correct for adjusting the blend door or do they need to be revised?

HVAC Blend Door Motor Troubleshooting

[DAVES89]

Ronnie,

 I think what Mc_Reatta said works well for troubleshooting, however for adjusting on a working unit I would defer to what the repair manual says on pages 1C-24 or 1C-26 [They are the same]. As soon as I did that everything worked great.

 I don't believe I adjusted trying to follow Mc_Reattas tutorial. I ended up with where the threads start in the clip, but when I adjusted it following the repair manual I was way to the end of the rod. 

 What I did was this;

 Remove rod from right side clip. Program to high heat high fan. Watch for arm to move to the full right position. Push rod to left to hear vent door close [[You will also get full resistance]. Put rod in clip. Set for auto fan and full cold, sit back and wait for A/C to turn on. Rev car to 2000 RPM's and watch your temp gauge in center vent drop to 40-42 degrees [w/r-12].

[DAVES89]

I thought I would look at the 'vert's HVAC system. The air flow out the vents are good so I thought I would check into what the rod adjustment was like. It is exactly what I have the Red set at [the clip way to the right end of the threaded part of the rod]. I then started the car and set it at 60 degrees, high fan, and bi level. Sitting in the garage I got 52 degrees. So I am going to clean everything as I did with the Red and then take my new purchase of r12 manifold a/c gauges over to my friends house with a can of r-12 [if needed] and get this one ready for summer.

[DAVES89]

Just got in from cleaning the plenum and condensor/radiator on the 'vert.  My air flow through the vents has improved and the A/C is now down to 44 degrees through the center vent set at high fan 60 ndegrees in Park with engine at 2000 RPMs

 I guess I am done, and ready for the heat! 

[padgett]

Still a little high (I see 36F) but needs more air flow at the radiator than just the fans.

[DAVES89]

Actuall I did a little better then that. I tried again and when I started the car I saw it was set at high fan 65 degrees. When I set it to 60 degrees I got 42. So I believe you are right Padgett, if I had a box fan in front of the car I could get my last 2 degrees [40]

 I learned much these last two weeks regarding heat transfer and it's effect on A/C operation...

Edited June 8, 2015 by DAVES89 (see edit history)