awilli6

Hey gang,

I'm still trying to sort the AC on my 87S4. Changed out everything (EV, Compressor, drier). Cleaned entire system. Pulled vacuum and charged it myself (~32 oz). Rear AC is ice cold. Front is cool. Did Dewayne's vacuum check. Actuators hold, solenoid are good. Holding vacuum across the board. The front still won't get cold.

1. Is it possible to be low on freon and the rear still blow cold?
2. Is there something else I'm missing?

awilli6

I have the heater bypass zip tied

Ducman82

i thought the cars with rear AC took more? i think i added 32 to my car....

Mrmerlin

my bet is one of the HVAC doors is out of adjustment or you have a leaking pod thus not closing the flap all the way
Get an IR gun and shoot the expansion valves whatever you see at the valve is what you should be seeing at the vent outlet.

awilli6

All actuators are holding vacuum. I'll get an IR gun and check.

joejoe

42.3 oz r-12 for '86.5 with rear air. Thought '87 on was same. If changed to 134 then not sure, but I think would be less. On both my '86.5 cars the rear is also ice cold, but front suffers.

awilli6

It's been changed to 134. I got the amount from one of the write-ups on Rennlist.

Kevin in Atlanta

Remove the center vent and with the rear a/c off and the front blower on its lowest setting what is the temp at the core? On my 91 S4 it is 36. I found the faster the fan speed the warmer the air. I use digital thermometer probes exclusively.

Randy V

Mine does the same. Why would that be?

Kevin in Atlanta

Air spends less time being cooled. I also suspect there might be blocked fins that force the air around the core rather than through.

Way back when we had a brand new Accord Prelude with A/C that disappointed - dealer said to use slower speeds.

Alan

It is always that way, faster speed = less time spent in the heat exchanger, it also means a higher total exchange of heat energy which increases the temperature of the heat exchanger (evaporator here).

So you can get a weaker colder flow stream at lower fan speed. But if it's really hot you need a higher total heat load reduction in the cabin - and you get that with higher airflow - even if it is not ultimately quite as cold. Higher airflow rates onto your body also aid in personal evaporative cooling (especially if you are hot enough to be sweating) - so it adds a subjective benefit over the actual temperature reduction which is likely why we don't perceive this effect much - it's usually a surprise to people when they measure it...

Once you have reduced the effects of heat soak in a parked vehicle - you may be able to stay quite comfortable (or more comfortable) with a cooler reduced flow. Which is exactly what most of us do - high fan -> lower fan. We'd likely also do this anyway for noise reduction and to avoid eye irritation from the high fan... But we know it works subjectively

To the OP: You could have a poorly operating front evaporator valve, poor cooling fan operation on the condenser or just a low freon charge - the rear evaporator is lower mounted so will get a better flow when there isn't enough to go around. The rear fan moves less air than the front so doesn't suffer so much from the air speed issue above - and the rear is always in recirculation mode. If the front has recirculation flap issues (always fresh air) or if it has comb flap issues (no bypass) then even with water valve closed (and it could be leaking...) a heat soaked car on a hot day will not have console vent air as cool as it could be...

Alan

giddyupp

Im pretty sure that if the rear AC is ice cold the system its self is fine. It must be one or more of the flaps not operation correctly. I had exactly the same problem on my '88. I replaced the 3 main valves in the dash and everything worked perfectly.

dr bob

Have you replaced the heater control valve? It may be leaking by even when closed. Easy test: with engine cold from overnight, start the car and turn on the AC. Front really cold? Then get warmer as the engine warms up? Suspect the heater control valve.

awilli6

I have replaced the heater control valve. Fresh off of an intake refresh. When I check vacuums all hold fine. In this Memphis heat I need good working AC. & the car is black w/ black interior. I'll get an IR gun to check vent temp. Even on low speed first thing in the morning air is noticeably warmer than rear. I ordered another rubber manifold that connects to all 5 solenoids. Gonna check the auto vent adjustor under the dash & glovebox. Trying to get it cold for Memphis to DC trip at the end of the month.

MainePorsche

Last thing to do then if all else checks out well, is a cleaning of the front evaporator. Is a simple thing to do. Peel back the rubber boot between the fan out flow track and the evaporator inflow. Get some AC coil cleaner spray from Lowes, and with a narrow beam light and toilet brush, spray the evaporator and gently brush off soilage on the evaporator. Carefully with a brush extension, vacuum the area out. Will optimize temperature exchange, and smell better too.

Add: my evaporator was slightly soiled with most of it being along the inferior border. After the cleaning was a shiny silver.