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1995 Buick Park Avenue --- A/C problem ---fan and ...
Sent to Car Experts May 23 02:13 PM

1995 Buick Park Avenue --- A/C problem ---fan and freon circuit AOK if the compressor clutch closes. All freon circuit switches OKay. Problem seems to be in the Automatic temperature control system. I have to drive several miles before cooling starts and then cooling cycles every couple miles from cooling to no cooling. The "in vehicle thermastor" appears to be OKay. Where do I go from here?
Roy Weise   royyz@commspeed.net

 

Optional Information:
1995 Buick Park Ave. 3800

Already Tried:
Freon circuit AOK Problem is in automatic control system.

Customer (name blocked for privacy)
Status:  Closed   Value: $25
Answer
May 23 2:26 PM (13 minutes and 4 seconds later)
         
REPLIEDCheck Mark

The refrigerant system needs to be verified with pressure gauges. You might have too high a head pressure cauing the high pressure switch to cut off the compressor. This can be due to overfilling of refrigerant, restricted orfice tube, restricted high or low side, or faulty a/c compressor. Also, if the condensor is restricted at the fins this will cause this as well, or the condensor fan is intermitently operating. These are the more common reasons for intermitent cooling on this vehicle, if the control head is at fault the pressures need to be identified first, before procedding the diagnosis, otherwise a control head can be misdiagnosed.

-Rip



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RIP -- Lead Technician -- 100% Positive Feedback on 2108 Car Accepts
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Reply
May 23 3:06 PM (40 minutes and 24 seconds later)
         
Reply to RIP's Post: No No --- As I said --- the freon system is AOK --- verified with all the usual pressure tests---switches are also AOK
The problem is in the "automatic temperature control" system. It is not sending the correct signal to the "Powertrain Control System" (PCM) that activates the compressor clutch. If the clutch is artifically closed, the freon system works just great.
As I said earlier, the "in vehicle sensor" seems to be with correct operating resistance/ temperature range. Got the picture?
Customer (name blocked for privacy)
Answer
May 23 3:31 PM (24 minutes and 46 seconds later)
         
REPLIEDCheck Mark

You mentioned that the compressor clutch engages in the original post, this tells me that the signal from the control head is good, however, now you state the compressor clutch does NOT engage- correct? That you are powering the clutch manully?I believe I misunderstood the question. If you are manully operating the clutch, than to properly diagnose the HVAC programer a Tech 1 scan tool needs to be used to retrieve diagnostic codes relavant to the sensors, do you have access to one? If not you may be able to make some basic checks to help identify the programer has failed and is indeed not sending the "a/c request" signal to the PCM. What wire are you checking the signal on or what programer terminal? And what is your reading? Also, just to be sure, have you checked the fuse # 5 (15 A) at the relay center? What about the a/c compressor control relay? Let me know the specifics of you findings on the signal to the PCM, and I can let you know where to go from there. Thanks,

-Rip



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Reply
May 23 4:11 PM (39 minutes and 59 seconds later)
         
Reply to RIP's Post: No Tech 1 scan unit available. The only sensor used in this application is the "in Vehicle sensor" and it appears to be OKay. Fuse #5 OK. Compressor control relay is OK.
By setting the temperature to 60 degrees, the cooling system performs OK in 1-2 blocks indicating all components of the freon/electronic system OK except for lack of proper invehicle temperature control (anything less than 60 degrees).
Access to the signal from the control unit to the PCM is really not readily avaiable for any measurement.
Guess all fingers are beginning to point to a faulty temperture control unit ($$$).

Customer (name blocked for privacy)
Answer
May 23 4:24 PM (13 minutes and 4 seconds later)
         
REPLIEDCheck Mark

Actually this vehicle has (4) sensors to let the programmer know how to control the climate. The Ambient Temperature Sensor, In-vehicle Temperature Sensor, Left Solar Sensor, Right Solar Sensor. If any of these are incorrect or faulty will cause loss of temp control, this should be identified thru the scan tool, or replacing the programmer might not correct the symptoms. But you can verify loss of programmer signal to the PCM on the Dark Green/ White wire at the A/C High Pressure Cut-Out Switch, the signal enters here from the programer and than into the Pressure Cycling Switch before going to the PCM. If there is no signal here the programer may be faulty, but would still need to be verified behind the connector at the programmer itself to be correct.

-Rip



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Reply
May 23 4:52 PM (27 minutes and 35 seconds later)
         
Reply to RIP's Post: Yes I know there are 4 sensors but, I think only one affects this particular function.
For your info --- I am a 85 year old retired electronic engineer and have been a shadetree mechanic for 70 of my many years. I always buy the shop manuals for any vehicle I own --- I am really quite disappointed with these manuals --- often wonder if the authors have ever seen the items they are writing about! I am recognized at the local NAPA store.
I think I will install a toggle switch to control the compressor clutch while I look for a replacement control unit at the local "junk" yard.
Thank you for all your effort and, of course, I will accept your response so you can get paid.
Customer (name blocked for privacy)
Answer
May 23 5:00 PM (8 minutes and 28 seconds later)
         
REPLIEDCheck Mark

A 2nd hand unit is a good idea, infact you may research online. If you have a opportunity to run it by the dealer for a scan of the programmer, this would at least elliminate those possibilities. Also if the ambient temp sensor doesn't read correctly, it will cease operation of the clutch/compressor. If you can forward an e-mail address, I can send you detailed system operation and testing, from Michell-On-demand, a proffessional atomotive information source. Thanks,

-Rip



Please click on "ACCEPT" if I was helpful-or if you still need assistance just reply, before leaving any feedback thanks
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Reply
May 23 5:29 PM (29 minutes and 15 seconds later)
         
Reply to RIP's Post: Didn't know about the ambient sensor affecting the control operation --- it seem to be operating OK.
My e-mail address is:
royyz@commspeed.net
and i would appreciate that info.
Thanks again,   Roy
Customer (name blocked for privacy)
Answer
May 23 6:42 PM (1 hour and 12 minutes and 11 seconds later)
         
ACCEPTEDCheck Mark

Sorry it taking long, it's approximatly 23 pages, i'll be sending it shortly. Thanks,

-Rip



Please click on "ACCEPT" if I was helpful-or if you still need assistance just reply, before leaving any feedback thanks
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RIP -- Lead Technician -- 100% Positive Feedback on 2108 Car Accepts
A.S.E. Master Technician, Advanced Level, Smog - European, Domestic, & Asian -- Car Category Mentor
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