ac not cold
 

i have a 1991 190e 2.6 ac starts out cool then turns warm. I think it might be the mono valve,I have gone threw the parts catalog but do not see a listing. If the car has one where is it and how do i get the rebuild kit. :confused:

A quick way to check for water flow is to feel both heater hoses while the engine is hot and running. If the inlet and outlet are hot you have water flow. ( some systems use one in and two out so be sure to check all hoses. )

Do you have access to AC pressure gauges? If while the AC is on the low side goes to zero and the high side goes very high , the expansion valve is sticking.

Monovalve is under the leaf cage on the passenger side right behind the fire wall. Unless you live somewhere where the temperature drops to the negatives, I would remove the aux water pump and put in a manual ball valve in its place. I close the valve during summer to stop coolant flow and I open it in the winter.

eBay for good used parts with warranty
 

Both the mono valve and the aux. water pump are found for good used prices on eBay. Make sure you get a decent warranty for each from a seller with a long history of positive feedback and the listing description shows they know what they are talking about.

He's not positive it is the monovalve. I would hold off on the purchase until you can get the other one off and test it. What I did to test mine was removed it and tried to blow water through it with the vacuum lever up which should close it and not allow water to pass through. Or just remove it and hold it under the faucet and move the lever to see if there is water flow. If there is, I say you use the copper ball valve mod. No cheap plastic parts to wear out. I've been good for several years now.

W201 has no monovalve like the W126.

W201's heater function is done by a vacuum controlled valve.

Photo of valve here, next to blower box thing.
Mercedes-Benz Forum - View Single Post - 190E 2.6 Heat coming from both vents in the cabin

Check to make sure the HVAC system is getting vacuum. I recall accidentally disconnecting mine near the brake booster and getting heat.

Could be vacuum leak too.

A/C gauges
 

:eek::):)yes I have gauges and the expansion valve is new last year, dryer and it ran fine felt it drop suddenly that's why I thought mono valve but as another member said it has no mono valve but a vacuum valve I will look into it but for now I am working on our front end back hoe, that has to come first. :eek: