Intruder196

My AC wasn't blowing cold enough. So I added a can of Freon. I think I may have overcharged it because the AC pressure switch blew out and leaked out all the Freon. I replaced the AC switch, then I vacuumed the system and recharged. But it doesn't blow cold enough. It has only 65 degrees F out of the center vents and per Clarks Garage for ambient temp of 90-100 degrees the low side should be 45-50 psi the high side 225-250, and the temp from the center vent should be 52-60 degrees. I only put in 24 oz of refrigerant.

I checked the plastic clips that are commonly broken up under the drivers side. But both of them are good.

Does anybody have any suggestions on what to check next?

When the AC is on should the Heater Control Valve be open or closed? or does it even matter?

Intruder196

oh, and this is for my '86 NA if that helps.

Tiger03447

IMHO the water control valve to the heater should be closed to keep hot water from circulating through the heater core. That alone might be enough to lower your vent temps.

Bill Lynch

You noted what the pressures should be but what are yours? If your low side is high but drops under higher RPM I would look at the expansion valve. If the pressures are close even under load it might be your compressor. Are you running 134 or r-12?

Intruder196

Those are my pressures as I charged it. I charged it until I reached the max pressure for ambient temp, per Clarks. I had been converted to 134 before I bought the car. The compressor is not original. It was replaced when the 134 conversion was done.

Intruder196

That's why I was asking. The valve stays open when the AC is on.

SloMo228

I think the heater valve is the only thing regulating heat coming out of the vents. If it's still open with the AC on, your HVAC system is trying to simultaneously cool and heat the air coming out of the vents. I'd start by replacing the heater valve. It's cheap and it's a good preventative maintenance item anyway.

Intruder196

HCV's are open by default, correct?

I can watch the lever move by applying suction to it. At idle I don't get enough vacuum to move it to close.

I checked for old or rotten vacuum fittings and didn't find anything. Should I pursue this as a possible vacuum problem before buying a HCV?

Jfrahm

In my 968 I need to rev it a bit to charge properly or it ends up undercharged. At idle of about 800 RPM the low side pressure is much higher than it is when goosed a bit.

SloMo228

Correct, they're open by default. I recently replaced my valve because it was staying open most of the time. The arm would move when I applied a vacuum, though, so I initially thought the valve was fine. I replaced all the vacuum lines and still had the issue. When I got the old valve off, it became clear that there was a slight tear in the vacuum diaphragm, as applying a vacuum would move the lever and close the valve, but the vacuum would bleed off and the arm would open again. Apparently the engine wasn't creating enough vacuum to keep the valve open consistently.

So, it could be either one. On mine, the valve is located next to the oil filter and is easy to remove, so it's not a big deal to swap out. My last 944 had it above the bellhousing and that one was a royal PITA to change.

Tiger03447

SloMo has it right, with the simultaneous heating/cooling..both the evaporator and the heater core (in most cars) are in the same box under the dash...Although I haven't checked this out in my early car, I suspect the same is true for Porsche.

Jay Wellwood

On my previous 928, I'd zip tie the Heater Valve closed just to make sure it stayed closed in the Summer months to ensure maximum cooling.

Besides this, you mentioned that you replaced the pressure switch, evacuated the system and then recharged it.

Did you replace the dryer/filter as well? Someone mentioned the thermal expansion valve as a potential culprit. Either of these could affect your cold air temps.

Intruder196

I did not replace the dryer. That has a filter in it? Perhaps I should since they dont seem to be too expensive.

Where is the thermal expansion valve located on a 944/2?

Jay Wellwood

I'd start with the Heater Valve. If that doesn't work, then re-check your charge numbers.

Sorry, I'll be the first to admit IDK where your TXV would be.

If you end up diving deeper - and by that I mean re-evacuating and recharging, I'd look at replacing the Dryer as it's pretty cheap insurance to ensure minimal amount of blockage in the system.

mytrplseven

I'd start by putting a tie wrap around the HCV lever to hold it closed to see if the A/C is coming out cold enough. If it is, then I'd replace the HCV. If the engine is running fine, then I wouldn't suspect insufficient vacuum to the valve.