AC system poor cooling
10-13-2012, 01:11 PM
#1
Rennlist Member
Thread Starter
AC system poor cooling
I recently had the compressor off to have the seals replaced. I sealed/ capped off the system as soon as opening the lines.
On reassembly I pulled a vacuum for 10 hours and then charged with R134. I had converted the system previously having flushed and replaced the dryer and expansion valve. I have dual electric mystique fans and the AC fan is operational.
At 1500 RPM with fan speed at 2 and OAT at 78 deg I am running 38psi low side and 280 high side. Air temp at the vent is only 60 deg.
I previously replaced the heater valve with a petcock type valve and have it closed.
What I have not checked is that the recirculate foot well flap is closing. Looks like it should close to put the system into recirculate versus pulling air in from outside.
What other things should I be looking at?
On reassembly I pulled a vacuum for 10 hours and then charged with R134. I had converted the system previously having flushed and replaced the dryer and expansion valve. I have dual electric mystique fans and the AC fan is operational.
At 1500 RPM with fan speed at 2 and OAT at 78 deg I am running 38psi low side and 280 high side. Air temp at the vent is only 60 deg.
I previously replaced the heater valve with a petcock type valve and have it closed.
What I have not checked is that the recirculate foot well flap is closing. Looks like it should close to put the system into recirculate versus pulling air in from outside.
What other things should I be looking at?
10-13-2012, 02:30 PM
#2
Rennlist Member
Rennlist Site Sponsor
If you have a low-side pressure of 38 psig, with no air or moisture present, the evaporator temp will be 43 deg F. A low-side pressure of 28-30 psi will give temps of about 32 deg F.
The fact that you might not have hot coolant present doesn't mean that you are getting the coldest possible output air temp. If the blend door is mixing non-cooled air passing thru the heater matrix with the cooled air passing thru the evaporator core, you will get output air temps somewhere between the 43 deg of the evaporator and the input air temp.
Possibilities include maladjusted blend door, faulty blend door foam seals, faulty temp control system, partially blocked evaporator air flow, missing underhood seal allowing hot engine air to enter the HVAC intake, etc., etc.
The fact that you might not have hot coolant present doesn't mean that you are getting the coldest possible output air temp. If the blend door is mixing non-cooled air passing thru the heater matrix with the cooled air passing thru the evaporator core, you will get output air temps somewhere between the 43 deg of the evaporator and the input air temp.
Possibilities include maladjusted blend door, faulty blend door foam seals, faulty temp control system, partially blocked evaporator air flow, missing underhood seal allowing hot engine air to enter the HVAC intake, etc., etc.
10-13-2012, 02:54 PM
#3
Race Car
Those pressures and temperatures show that your system is probably slightly overcharged. But as Wally stated, that isn't really your problem because even at 38psi low side you should be getting lower output temperatures. I would look at the recirculation flap first. If it doesn't close, the system is continually trying to cool 78 deg F outside air, and it can only drop the air temp by 20 - 30 degrees. It's like pouring water over an ice cube continually instead of putting that ice cube in a glass of water. In the glass, the water eventually gets really cold, but when you are pouring water over it, the ice can only cool the water a little as it flows by for those 0.5 seconds or so.
Dan
'91 928GT S/C
475hp/460lb.ft
Dan
'91 928GT S/C
475hp/460lb.ft
