99 A4 1.8T tip 80K. annoying A/C problem. A\C stops cooling(compressor truns off and recirculation de-selected on HVAC controller) if RPM drops below 2000 RPM. A/C work fine if car is started and left in park or kept above 2000 RPM. It take about 2-3 minutes of driving for A/C to trun off. I suspect some type of temp sensor, except rpm is the key(soon as rpm goes above 2000, A/C back on. A/C charge checked. I found a large vacuum leak, car runs smoother(but a/c STILL BAD). Twice now I have seen my outside temp go to negative numbers, during initial start(but a/c always works fine for 2-3 minutes). Here is VAGCOM. Using tip sift mode to keep rpm up. Need help.

1. Were does computer and HVAC get rpm input.

2. I see RPM range on OBD HVAC diagnostic. What is the normal range?

3. Could the temp sensor trip A/C off line.

4.could alternator voltage be a problem?


2 Faults Found:
17953 - Throttle Valve Controller: Malfunction
P1545 - 35-10 - - - Intermittent
17966 - Throttle Actuator (G186): Electrical Malfunction
P1558 - 35-10 - - - Intermittent
Readiness: 0000 0000
-
Address 02: Auto Trans Labels: 8D0-927-156.lbl
Part No: 8D0 927 156 BM
Component: AG5 01V 1.8l5VT USA 8508
Coding: 00000
Shop #: WSC 00000
1 Fault Found:
00526 - Brake Light Switch-F
27-00 - Implausible Signal
-
Address 03: ABS Brakes Labels: 8E0-614-111-EDS.lbl
Part No: 8E0 614 111 B
Component: ABS/EDS 5.3 FRONT D00
Shop #: BB 24332
No fault code found.
-
Address 08: Auto HVAC Labels: 8L0-820-043-2D.lbl
Part No: 8L0 820 043 D
Component: A4 KLIMAVOLLAUTOMAT_D75
Coding: 04142
Shop #: WSC 06335
No fault code found.
-
Address 15: Airbags Labels: None
Part No: 8D0 959 655 M
Component: Airbag 7 Audi 0502
Coding: 00104
Shop #: WSC 06335
2 Faults Found:
01218 - Side Airbag Igniter; Passenger Side (N200)
32-10 - Resistance too High - Intermittent
01217 - Side Airbag Igniter; Driver Side (N199)
32-10 - Resistance too High - Intermittent
-
Address 17: Instruments Labels: 8D0-919-xxx-17.lbl
Part No: 8D0 919 910 P
Component: B5-KOMBIINSTR. VDO D05
Coding: 02242
Shop #: WSC 00000
No fault code found.
-
Address 35: Centr. Locks Labels: 8D0-862-257.lbl
Part No: 8L0 862 257 N
Component: CV-Pump D10
Coding: 16140
Shop #: WSC 06335
3 Faults Found:
01371 - Alarm triggered by Door Contact Switch; Driver's Side
35-00 - -
01370 - Alarm triggered by Interior Monitoring
35-00 - -
00955 - Key 1
09-00 - Adaptation Limit Surpassed
-
Address 45: Inter. Monitor Labels: 4B0-951-173.lbl
Part No: 4B0 951 173
Component: Innenraumueberw. D03
Coding: 00101
Shop #: WSC 06335
No fault code found.
-
Address 56: Radio Labels: None
Part No: 8N0 035 186 A
Component: Radio D03
Coding: 00113
Shop #: WSC 06335
No fault code found.
End -

 

I'm having the same exact problem with my a/c swithing on and off along with the dash/outside temp dropping to the negative numbers. Is it the ambience temp. switch/sensor? I'm assuming you might have fixed it already since you posted a month back. Any suggestions are greatly appeciated.

Thanks,
Henry

96 B5 A4 2.8 5spd

 

The AC/heat operate based on what the ambient temp reads. So if its 90* out and you hit 'auto' then it will know to pump out cool air and opposite when its cold outside. If your temp reading is way off its likely that is what is causing your AC to switch off.