I cannot figure out ths a/c problem. I bought this car a few months ago so I do not the history. It has a R134a compatible compressor (has a label on the side). It has a R134a retrofit sticker on the rad support. It has a R12 fitting on the low side line and on the compressor. It has built on R134a fitting on the condenser. I cleaned the condenser, new fan clutch and wired both the aux fans so the run when the compressor is on. Hi side @ 1500 rpm is 280 and low side is 30 psi. The temp at the vents will not get below 70 F at highway speeds. At idle it is the high 80's. The HVAC pods are working, I can disconnect the compressor and the the system will blow ambient temp so I do not think the heater is bleeding air. I am pretty sure it has R134a and the numbers are a little low but it should cool better that this. The low side line does not seem to be overly cool. I know R134 does not work as well as R12 but it should be better than this. Any other ideas on what to check?

Another question concerning the HVAC controls (aka Rubiks cube of the HVAC world). To get maximum cooling the center vents are closed and the a/c comes out the side vents? If I open the center vents slighty warmer air will come out.

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning

The pods are working correctly. I checked each one and they are holding a vacuum, even the one that when it leaks hot air comes through the vents all the time. I even ran the system with the compressor clutch disconnected and checked the temp of the vent air for hot air from the heater core. I was barely above ambient which says to me that the pods are working and not letting hot air through.

Yes, I wires both of them up so they are both are on when ever the compressor clutch is on.

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning

Actually, I don't think the pressures look too bad for 1500RPM/stationary/DFW heat & humidity. The old MBs ran pretty hot on the high side.

Might be a bit overcharged - I'd like to see it stabilize at 25 on the low side. But that shouldn't account for the almost complete lack of cooling you are seeing.

Is the low side plumbing sweating? Check the temperature of the high side plumbing, see if it changes from hot to cold before the expansion valve. If it does, you've got a restriction. Has a sealer been used in this system (That one's for Larry...)

This is a 201 chassis, correct? I'm not so familiar with the HVAC system on those. I think they use a more conventional setup with no monovalve to regulate the heater core, but rather use a blend door to direct the airflow across or around the heater core. I'd be looking for problems there. Is it possible to block coolant flow to the heater core, perhaps by pinching off a flexible hose? Might be interesting to try it.


My $.01 (I don't think I have 2 cents worth of advice to offer here...)

The high side is the same temp as far as I can touch, hot. I thought about blocking the water to the heater core to rule it out but ambient air comming from the vents. I can unplug the compressor and turn on the a/c. The air is still going through the HVAC system. The air comming from the vents is very close to ambient.

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning

I made a little progress. I took the cowl grill off and realized the vacuum line was disconnected from the heater shutoff valve. When I feel the air comming from the center vents I can feel different temps depending where I hold my hand. I will double check vacuum going to the pods. I also check the temp of the low pressure line comming from the evap. It was about 43 F. So this is telling me there might be an air flow issue.

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning

It's normal for the low side line to be cold and sweating all the way back to the compressor. So no problem there, and in fact it shows the system is working.

I think you have an airflow issue. Is it possible the a/c evap is so crudded up/blocked with years of debris that heat transfer from the air simply isn't happening?

I've never seen a car in which the control flaps can direct air around the a/c evap. The heater core, yes, but not the evap.

The temp difference is weird. The center vent is also slightly warmer than the outers. One thing is when the center vent is open you can see the heater core, I am thinking a little heat is comming from that.

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1987 190DT, clackity clack
90 Mustang track car
95 Lightning