FredR

My a/c system has been working very well since refurbished the compressor over a year ago and i have not had to top up the gas at all until now [possibly].

sad to say i have plenty of experience of the gas leaking so this run has been most welcome. What I am somewhat puzzled by is the behaviour over th elast couple of weeks. on hte last two occasions I ran the car it started with the a/c working and as the motor warmed up, after about 5 minutes or so the a/c stopped working. I cannot say i have seen this characteristic before but just wondered if any of you chaps have seen similar behaviour when gas pressure was marginal.

I would have thought that if the pressure was a bit low when cold, that maybe the heat soak would increase overall pressure a bit and keep it from tripping the low pressure switch. I will be topping up the gas assuming the pressure is a bit on the low side.

Any thoughts?


Regards


Fred

docmirror

Heater valve switch at the rear firewall near the top.

Bilal928S4

And your heating valve is bypassed? Correct?

SteveG

Refrigeration is based on the interaction of magnets and magic.

You are working in the dark if you don't have gauges on there to tell you what pressures are in the system.

FredR

Bilal,

Correct- the heater valve is fitted and in the closed position to prevent the coolant bypassing the radiator- no coolant running through or in the heater core at all.

Rgds

Fred

docmirror

Unless the throttle plate in the heater valve is melted. Check the car with the AC off, and see what the temp of the air coming out is after warmup.

joejoe

Low gas charge will present as you described. (at least for r-12)

FredR

There is no coolant piped to the heater core at all. The valve is there purely to act as a block in the hose returning coolant to prevent coolant recycling past the radiator so no heat can work its way into the cabin from the coolant circuit.

Also the freash air flap is locked closed after actuator failure so I am not trying to air condition the Middle East.

Regards

Fred

docmirror

Oh. Not sure I understand the post, and clearly you have a modified setup so I will withdraw. Good luck.

j.kenzie@sbcglobal.net

I agree with Joejoe. Low refrigerant will cool at first but not have capacity for continued cooling. Do you have a/c gauges? You could have a secondary leak which eventually showed up after fixing the compressor leak. The heater valve could also be leaking hot coolant into airstream, due to melting or other distortion, in spite of being wired closed. A new heater valve, wired closed might fix that.
Good luck,
Dave

dr bob

Fred-

The symptom you describe with the compressor cycling off after five minutes of engine run is not typical to low system pressure. Generally, once the compressor is running and heat is being pumped around the system, the pressure safety switch will remain closed. It's in the high-pressure side of the system, so adding heat only makes that pressure increase. Go ahead and verify that you have appropriate system pressures. I don't see that as a direct possibility though.

Does the system cut out the same way with the engine idling for the five minutes? If so, you can do some electrical sleuthing under the bonnet. Look for the current flow path through the anti-freeze switch near the base of the windscreen, then back through the CE panel to the harness for the pressure switch, through the 14-pin connector, the compressor clutch coil connection on the front-of-engine harness near the dipstick tube. This is the same process used to identify a failed control head relay, by the way. Someplace in your meter testing, you'll discover what's interrupting the current flow to the compressor clutch, and keeping your system from running.

dfrhodes

when you say the A/C stops working, do you mean the compressor clutch deactivates? or it just gets warm inside? if compressor cuts out, could be any number of things- over pressure limit, freeze switch, controller issue, etc. Have you cleaned your evaporator and compressor?

alabbasi

I'd start with the heater valve. As the motor warms up, you'll get hot water running through the heater system which could cause those symptoms.

Your high pressure switch may be cutting in if your system is over charged or if the cooling fans are not engaging.

Check your pressures and get back to us with the gauge readings and temps.

Alan

is this an R134a converted system? did you add the 3 way pressure switch?

Could be too high of a pressure cuts it off, this happens especially in a late model GTS when one cooling fan quits...

Alan

FredR

Bob,

I have plenty of experience losing gas sad to say and this is the first time I have seen this characteristic- hence this post. I have not ruled out fugitive loss of gas but I am suspicious this is not the only problem here.

Trouble is it is a bit of a bugger playing around on the ctar now that the summer heat has kicked in big time and even worse driving around with no a/c! Fortunately I do not need the car on a daily basis.

It would be interesting to take the individual permissive elements out of the loop to test and thus see which one is breaking the solenoid circuit.

Regards

Fred