Ac not cold after few miles
05-27-2023, 06:29 AM
#1
Ac not cold after few miles
Hi all,
Hope this finds you well.. I have a 1988 928 s4. Did a serious renovation work all around including a new "denso" ac compressor. The issue is.... At a cold start, the ac blows quite cold and temperature feels reasonable.. However, after few miles it seems that the cooling temperature drops. This is Also valid at a full engine stop for an hour or so.. Ac seems no that cold!
Any feeback would be highly appreciated..
Bahaa
Hope this finds you well.. I have a 1988 928 s4. Did a serious renovation work all around including a new "denso" ac compressor. The issue is.... At a cold start, the ac blows quite cold and temperature feels reasonable.. However, after few miles it seems that the cooling temperature drops. This is Also valid at a full engine stop for an hour or so.. Ac seems no that cold!
Any feeback would be highly appreciated..
Bahaa
05-27-2023, 06:46 AM
#2
Team Owner
Did you service the HVAC system vacuum pods in the dash
928GT.com has a good description look for Wally’s HVAC system review
Is the system fully charged.
What type of refrigerant are you using
what type oil did you use
928GT.com has a good description look for Wally’s HVAC system review
Is the system fully charged.
What type of refrigerant are you using
what type oil did you use
05-27-2023, 10:28 AM
#3
Rennlist Member
The most likely cause of what you describe is the relay in the ac control unit. As the unit heats up the relay fails and power to the solenoid operated clutch on the ac compressor drops out. These things can cycle on and off at random.
Simple test is to temporarily run a 5 amp fused connection from the hot post to the clutch solenoid. Easiest way to do this is to pull the black wire out of the 14 pin connector [next to the hot post in the engine bay] on the engine harness side [pin number 9]
Simple test is to temporarily run a 5 amp fused connection from the hot post to the clutch solenoid. Easiest way to do this is to pull the black wire out of the 14 pin connector [next to the hot post in the engine bay] on the engine harness side [pin number 9]
The following users liked this post:
Babado (05-29-2023)
05-27-2023, 10:31 AM
#4
The most likely cause of what you describe is the relay in the ac control unit. As the unit heats up the relay fails and power to the solenoid operated clutch on the ac compressor drops out. These things can cycle on and off at random.
Simple test is to temporarily run a 5 amp fused connection from the hot post to the clutch solenoid. Easiest way to do this is to pull the black wire out of the 14 pin connector [next to the hot post in the engine bay] on the engine harness side [pin number 9]
Simple test is to temporarily run a 5 amp fused connection from the hot post to the clutch solenoid. Easiest way to do this is to pull the black wire out of the 14 pin connector [next to the hot post in the engine bay] on the engine harness side [pin number 9]
05-28-2023, 08:34 AM
#5
RL Community Team
Rennlist Member
Rennlist Member
Also, what are your high and low pressures with the compressor engaged? Is the sight glass clear when it's running?
05-28-2023, 10:19 AM
#6
The AC vent vacuum pods, the AC head relay… all good investigative prospects. Add to that the low pressure switch, and some of our cars I understand have a high pressure switch. Either of which can brown-out and temporarily cut off the compressor.
There are lots of good reads on all of these in the forum. With ~30+ year old AC systems, getting cozy with the operation of our AC systems is a progressive necessity.
Super-Porsche “Gandalf” Dwayne posted a top-bottom trouble AC shooting link:
https://rennlist.com/forums/diy-928/...re-w-pics.html
There are lots of pictures there.
The anti-freeze switch may also come into play if you’re low on refrigerant and the evap temp gets too low. This switch will temporarily cut off the compressor until evap icing thaws. Dwayne’s article describes testing these things.
There are plenty of YouTube’s on how to use an AC manifold gauge set. Viewing these over a couple times will help prevent doing harm to the AC system while using the AC manifold gauge set.
I recommend this YouTube to get acquainted with the procedure of using the gauges, although this YouTube goes further into actually charging the system.
There are lots of good reads on all of these in the forum. With ~30+ year old AC systems, getting cozy with the operation of our AC systems is a progressive necessity.
Super-Porsche “Gandalf” Dwayne posted a top-bottom trouble AC shooting link:
https://rennlist.com/forums/diy-928/...re-w-pics.html
There are lots of pictures there.
The anti-freeze switch may also come into play if you’re low on refrigerant and the evap temp gets too low. This switch will temporarily cut off the compressor until evap icing thaws. Dwayne’s article describes testing these things.
There are plenty of YouTube’s on how to use an AC manifold gauge set. Viewing these over a couple times will help prevent doing harm to the AC system while using the AC manifold gauge set.
I recommend this YouTube to get acquainted with the procedure of using the gauges, although this YouTube goes further into actually charging the system.
The following 2 users liked this post by ZEUS+:
dimi5928 (05-29-2023),
husker boxster (06-04-2023)
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05-29-2023, 07:10 PM
#8
Rennlist Member
Welcome back ZEUS+.!
06-04-2023, 03:45 AM
#9
06-04-2023, 05:08 AM
#10
Team Owner
Can please describe exactly what you checked
Do you see clear liquid in the Drier sight glass or does it look like bubbles mix in
Did you check the vacuum pods for vacuum integrity usually 2 in the center console and one in the blower box
The defrost pod is not usually a leaking point on the left side console
What refrigerant is in the system
do you have rear air
who did the system rehab
did you use a sniffer to find leaks
Do you see clear liquid in the Drier sight glass or does it look like bubbles mix in
Did you check the vacuum pods for vacuum integrity usually 2 in the center console and one in the blower box
The defrost pod is not usually a leaking point on the left side console
What refrigerant is in the system
do you have rear air
who did the system rehab
did you use a sniffer to find leaks