Ok here goes, I have searched all forums to No avail. Here is what I have '82 300td, automatic. Here is what is happening.

Friday
Driving from Tyler to Waco. AC was ok everything cool but not as cool as I would have liked. I had just installed a newer high speed fan and it was working fine. On the return from Waco to Tyler I noted the AC was blowing a bit warmer than it had been, on my way to Waco. I played around with the thumb control turning it to maximum Hot and then back to maximum Cold. Thinking to myself this will be nice this winter, while turning the thumb control back to Cold. Here is the problem, it never got near cool again, I think it got hotter. I got out to check the High Speed fan and it was off and will not come back on. I cannot tell if compressor is kicking on.

Saturday
Still blowing HOT

Sunday
I stop at Orielys and purchese a can of 134a, drove to the house and connected the Idiot gauge that came on the can, it read to be in the Warning/Overcharge range. Below are the psi ranges on the gauge
Low range 0-25
Filled range 25-45
Alert range ? 45-65
Warning is65-200+

When I connected the I. gauge the ambient temp was 85f./29c outside. The reading came back with 100psi. and should be 45-55psi.

Plan on taking it to AC shop in the morning, unless you guy's can offer some guidance.

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

Were you checking that pressure with the compressor running?

Best to check the high side too. You may have a bad monovalve, if it's really blowing hot and not merely ambient.

Sounds like a possible monovalve problem. Have you applied voltage to the monovalve and confirmed that the plunger moves?

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Compressor was not running when I checked pressure. I will check highside, but Im not sure if the I gauge that came with bottle of 134a will give me a relevent reading?

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

That particular gauge will not attach to your high-side service port.

Without the compressor running, the low-side pressure reflects the average refrigerant temperature and is not related at all to the refrigerant level.

Have you checked the foam hose behind the glove box?

It's only an "idiot gauge" when you try to use it with the a/c system turned off!!!

When the compressor is not running, the high and low side pressures should be the same.

No, I have not checked a foam hose, not trying to be a smart mouth but what will I be checking for?

I did go out and run new wires to the monovalve. While I was inspecting it, I noted rat damage on the wires. Hoped by doing so I would have been in cold air. Did not do a thing. Boy's it is hot out there.

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

At this point, the easiest thing to do to troubleshoot the monovalve would be to clamp a heater hose.

OK, but as I said it is hot out there. I will be back in 20 minutes, with the answer.

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

OK I pinched it off with a rag and a pair of vice grips, and let her run with AC on High Cold. I got nothing but HIGH HOT! So I guess I will get a valve kit. So what else you guy's got. Im over being hot. Im energized

__________________
Collector of Fine Hose Clamps
'77 240D 'AVA' is in heaven now
'80 240D Kanarienvogel
'82 300TD 343k was my daily driver 'ADOLPH' In Surgery for a severe Deer Bite to the Nose
'88 560SL 102k 'White One'

I think that you need to get a manifold (gauge set) and get high and low side pressures at this point.

you should be able to hear the compressor click on ... in fact, the relay clicks before the engine starts in both my w123s

i recently replaced a bad relay (in the box above the DS front wheel) in our '82 TD that prevented the compressor and aux fan from getting any power. Compressor was fine, just not getting any power.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

If you remove the glove box liner you should see a foam hose going horizontally from a pipe to the thermal sensor that's at the center top of the dash board. These hoses commonly disintegrate and completely disappear.

Use a non thermal conducting hose. Foam pipe insulation from Home Depot works great for this.

Good luck,

Something's not right. If you clamped the correct hose, you should not have gotten HIGH HOT. Clamping the hose should have reduced vent temps to ambient (given enough time and airflow to cool down the heater core, if it had been getting hot coolant).

And a valve kit won't fix rat damage (unless the rat is inside the valve). Damaged wiring may leave the monovalve open and let heated coolant flow into the heater core.

If you have a multimeter, check the voltage across the terminals on the monovalve. When closed, you should read 12 V, and if you have an assistant cycling the temp wheel from max heat to max cool, you MAY hear or feel a click as the electromagnet pushes the piston.

If you somehow jumpered the monovalve to stay closed and gave the system adequate time to negate the already heated heater core, then you've probably got other problems.

To check the foam tube under the dash, pull out the glove box and look to the center. The "foam tube" is a connector from the cabin air temp sensor in the center of the dash to the blower motor - it's a tube, made of foam, and it rots and falls apart. The blower motor draws cabin air across the sensor and then the CCU adjusts accordingly. A rotted tube means minimal air across the sensor, so the CCU doesn't have good data to adjust the system. I don't know if the sensors are in use if the max settings are selected, but it is one more common problem.

You should be able to tell if the compressor is engaged by looking at the front of the compressor when your A/C is turned on.

The pulley will spin all the time. In front of the pulley is a triangular plate.

When the clutch engages, that triangle should spin at the same speed at the belt. If it's not spinning, your compressor is not engaging. There are numerous reasons for that to occur.

The gauge needs to be used on an operating system. The "low side" can't be low if the compressor isn't pulling.

Read here: http://www.aircondition.com/tech/questions/82/

And here: http://www.ackits.com/aacf/ptchart.cfm