A/C Troubleshooting questions...
08-29-2018, 03:59 PM
#1
Rennlist Member
Thread Starter
A/C Troubleshooting questions...
Compressor clutch stopped coming on.... When I hotwire directly to battery it works(still does not blow cold, added can of freon thinking it was in low pressure mode, still no joy). Tested known good A/C relay so does not appear to be that.... Looking at the electrical diagram there seems to be some interaction between the radiator temperature switch and the low pressure refrigerant switch that I dont understand ? In fact the wiring diagram suggests that the pressure switch does several things 1 obviously on low refrigerant pressure it turns off 2 it also appears that it will shut off on too high a pressure as well 3 There is a 3rd pressure that it looks like it cycles on?? 4 Lastly there seems to be interaction with the radiator temp sensor??
Could a bad radiator temp sensor cause the A/C compressor to not switch on? The odd thing is that the cooling fan has been cycling a bid odd lately but I just thought it due to the hot weather.
Ordered a new low pressure refrigerant switch. How likely is it that those go bad? Is it true there is a shrader valve under that switch and I can change without evacuation?
Could a bad radiator temp sensor cause the A/C compressor to not switch on? The odd thing is that the cooling fan has been cycling a bid odd lately but I just thought it due to the hot weather.
Ordered a new low pressure refrigerant switch. How likely is it that those go bad? Is it true there is a shrader valve under that switch and I can change without evacuation?
08-30-2018, 07:01 AM
#3
gauges would be the best way to troubleshoot to see if the system is shy of a full charge. as noted in your post, with the compressor jumped, it didn't blow cold. my R12 sticker says 33oz.
the high pressure switch grounds the fan relay. some switches are off-on-off to kill the system if the expansion valve gets plugged (or the head pressure is excessive)
the low side switch should show in series with the clutch on the diagram.
the high pressure switch grounds the fan relay. some switches are off-on-off to kill the system if the expansion valve gets plugged (or the head pressure is excessive)
the low side switch should show in series with the clutch on the diagram.
08-30-2018, 07:16 AM
#4
Rennlist Member
Thread Starter
gauges would be the best way to troubleshoot to see if the system is shy of a full charge. as noted in your post, with the compressor jumped, it didn't blow cold. my R12 sticker says 33oz.
the high pressure switch grounds the fan relay. some switches are off-on-off to kill the system if the expansion valve gets plugged (or the head pressure is excessive)
the low side switch should show in series with the clutch on the diagram.
the high pressure switch grounds the fan relay. some switches are off-on-off to kill the system if the expansion valve gets plugged (or the head pressure is excessive)
the low side switch should show in series with the clutch on the diagram.
If you evacuate a system and put a vacuum on it is it unlikely to unclog an expansion valve or is replacing the only remedy?
How about the odds of a faulty pressure switch vs plugged expansion valve?
08-30-2018, 05:10 PM
#5
Definitely have to get the proper charge to diagnose the switches. The off-on-off style switch doesn't flip on the fans until a certain pressure is exceeded. In the middle sweet spot the fans engage. When the head pressure is over the second threshold, the compressor gets turned off until enough heat is removed to bring the pressure back down.
My my kid knows an AC guy with an old dial-a-charge which makes life easy.
My my kid knows an AC guy with an old dial-a-charge which makes life easy.
08-30-2018, 06:21 PM
#6
Burning Brakes
"This is how my fan has been running lately...once up to temperature its runs on off on off on off"
Assuming this is in reference to the radiator cooling fans.
For late model: Check the radiator cooling fan resistors next to the battery under the cowl cover. It's next to the HVAC air intake system.
For early model: Pull the instrument cluster and check the firewall behind.
Same test for both models: Check with ohmmeter on lowest ohms setting, should read under an ohm. You may find only one of them is open. Replace both.
You may also find damaged wiring. Repair as needed.
Assuming this is in reference to the radiator cooling fans.
For late model: Check the radiator cooling fan resistors next to the battery under the cowl cover. It's next to the HVAC air intake system.
For early model: Pull the instrument cluster and check the firewall behind.
Same test for both models: Check with ohmmeter on lowest ohms setting, should read under an ohm. You may find only one of them is open. Replace both.
You may also find damaged wiring. Repair as needed.
Last edited by PaulD_944S2; 08-30-2018 at 06:55 PM.
08-30-2018, 08:01 PM
#7
Rennlist Member
Thread Starter
"This is how my fan has been running lately...once up to temperature its runs on off on off on off"
Assuming this is in reference to the radiator cooling fans.
For late model: Check the radiator cooling fan resistors next to the battery under the cowl cover. It's next to the HVAC air intake system.
For early model: Pull the instrument cluster and check the firewall behind.
Same test for both models: Check with ohmmeter on lowest ohms setting, should read under an ohm. You may find only one of them is open. Replace both.
You may also find damaged wiring. Repair as needed.
Assuming this is in reference to the radiator cooling fans.
For late model: Check the radiator cooling fan resistors next to the battery under the cowl cover. It's next to the HVAC air intake system.
For early model: Pull the instrument cluster and check the firewall behind.
Same test for both models: Check with ohmmeter on lowest ohms setting, should read under an ohm. You may find only one of them is open. Replace both.
You may also find damaged wiring. Repair as needed.
? I thought those resistors had something to do with the blower motor in the cabin, not the radiator cooling fans?
Trending Topics
08-30-2018, 10:58 PM
#8
The cabin fan has a separate resistor pack but the cooling fans use the pucks by the battery.
See if someone will throw some dye in the system before purchasing anything and check to see the can you added has held.
Usually freon leaks inside the cab leave little rainbow oily dots on the windshield. Another tell is disintegrated foam gaskets and seals in the ducts. If it bleeds down and you don't see any visible dye, pull the radio and check the condensate drain.
The wistle of a speck of dirt in an expansion valve is quite noticeable. You would hear it.
It's common to replace the evap core on the early 90s MBs. A nice twenty hour job on the w140. I picked up a subby RS coupe last week with a bad high pressure switch according to the paper clip test.
See if someone will throw some dye in the system before purchasing anything and check to see the can you added has held.
Usually freon leaks inside the cab leave little rainbow oily dots on the windshield. Another tell is disintegrated foam gaskets and seals in the ducts. If it bleeds down and you don't see any visible dye, pull the radio and check the condensate drain.
The wistle of a speck of dirt in an expansion valve is quite noticeable. You would hear it.
It's common to replace the evap core on the early 90s MBs. A nice twenty hour job on the w140. I picked up a subby RS coupe last week with a bad high pressure switch according to the paper clip test.
09-02-2018, 06:14 PM
#9
Rennlist Member
Thread Starter
Alright then, the local AC shop that said there is a shrader valve under the pressure switch was incorrect. Not on my 968. At least I know how much charge is in there ....... 0. Nice to know where you stand.
09-03-2018, 08:42 AM
#10
throw some dye to it and see what comes up. under hood leaks are easy to find but not so much in the interior. pull the radio and see if the housing is oily at the condensate drain.
it is best to replace the receiver/dehydrator if the system has been exposed. https://griffiths.com/porsche/air-co...4-944-951-968/
it is best to replace the receiver/dehydrator if the system has been exposed. https://griffiths.com/porsche/air-co...4-944-951-968/
