Kevin in Atlanta

1987 S4 140k miles
Was converted to 134A somewhere in its past.
Had the system evacuated and refilled about a year ago with poor results. I don't really use A/C that much so I ignored until I needed to defrost the windshield recently. I need to fix the A/C.

Compressor clutch engages and fans run.
Warm air all the time from front vents
Rear air is around 75 degrees - cold compared the front.

Front expansion valve inlet and outlet pipes are lukewarm to the touch. They should be too hot to touch on the inlet and frosty on the outlet.

I have everything I need to redo the A/C system -0 o-rings, drier/receiver and front and rear expansion valves.

I assume there is sufficient Freon in the system because the rear a/c does chill the air.

Could the front expansion valve be blocked?

I am just looking for insight before I replace every thing.

Kevin

FredR

Is your heater valve in the closed position [needs vacuum to close] & is the recirc flap closed?

75 degrees F? That is not going to cool anything- this suggests you are not flowing freon correctly so probably not the heater valve or the recric flap. If the clutch is engaging then logic suggests the low pressure switch is not a problem nor is the a/c relay.

Are you sure the clutch is not slipping as in friction material burnt out?

Regards

Fred

Rob Edwards

I think I'd start by putting a set of gauges on it and seeing what the hi/lo pressures are. Tells you a bunch in concert with the ambient temps/humidity RE: degree of charge, whether the compressor's compressing, blockages, etc.

Kevin in Atlanta

What are the correct ranges fro high and low side readings? I believe from my search here it s 325 High and 25-30 low side?

Better yet is there a chart with pressures and ambient air temperatures?

WallyP

My first guess is that the expansion valve is locked wide open, or the compressor isn't pumping.
If the valve were fully shut, the refrigerant pressure would go sky-high, and the compressor would lock up or break. If the expansion valve were almost shut or blocked, the high pressure line would probably be very hot and the low pressure line would be slightly cool.
The compressor valves could be broken, or the pistons could be toast.

griffiths

Rob has given you the first step in troubleshooting; you need to know the pressures. Beg, borrow or buy a good gauge set, learn how to use them and report back the low&high pressure and the ambient avg air temp around the car.

In a good working system the pressures are all relative to the volume of refrigerant in the system, the outside air temp, the temperature of the evap coils.

When you first test the pressures do it with the rear air off and engine at idle.

FredR

Kevin,

You also gave a clue that I did not spot in that "you do not use it much". In my experience not using the a/c results in the oil film on the seals to dry and then you get fugitive emissions - if you have not checked the pressure that is the first thing you should check.

Rgds

Fred

Kevin in Atlanta

I am actively looking for a set of gauges to borrow now.

MjRocket

Kevin

If you can't source a set locally to borrow I have a set you can use.

Mj

dr bob

For those playing along at home, R12 gauge ests are getting a liitle more rare thes days. While generally not expensive (yet) they just aren't as common as they used to be. If you see a name-brand set in good condition, it might be worthwhile snapping them up. The only "consumable" part of the gauge sets are the hose end seals (little rubber bushings), and the little pin depressors in the 'car' end of the two hoses; the pin depressors fall out when the hose seals fail and fall out.

These gauges, a temperature/pressure chart (Mollier diagram best if you know how to read one), along with a couple accurate thermometers (NOT an IR thermometer...), are the most basic diagnostic tools for the AC system.

Jim Devine

R12 gauge sets show up at flea markets & auto swap meets usually very cheap. Also places like EBAY, Craigslist etc. As usual, probably none to be found when you really need them, the time to look & buy is when you don't need them. A good leak detector is nice to have too.

Kevin in Atlanta

MjRocket offered a R12 gauge set - I have 134A - I found a Robinair from Amazon for 150~ I wounder if I should just bite the bullet and buy it./

MjRocket

Kevin

Check HF for 134A gauges, they have some for quite a bit less.

Mj

Kevin in Atlanta

Are HF any good?

MjRocket

I don't own a pair but I've used a set in the past, seemed to be well built and worked fine.

I'd say for how little they will actually be used they should last a lifetime.


Mj