A/C Blows Hot Air

[Sovereign]

Looking to solve an AC issue on a 1981 300d.

When I turn on the AC I only get hot air, usually very hot air. After reading through past posts I am assuming that my system needs recharging. Is it possible to use R12 on this model and if so where do I start?

I am correct inmy assumptions?

Any advice will be greatly appreciated.

Thanks

If you have "very hot air" the problem may be the monovalve (heater valve) being open and overpowering the AC. Start by checking fuse #14.

[carnut]

R12 is the correct freon. Should say so on a red sticker on the radiator brace.

[LUVMBDiesels]

Originally Posted by Craig

If you have "very hot air" the problem may be the monovalve (heater valve) being open and overpowering the AC. Start by checking fuse #14.

I agree. Check to make sure you have 12v on the monovalve first. It defaults to open which lets full heat go to the cabin.

[Sovereign]

I checked the fuses and all are in good working order. Also, I would like to retract my "very hot air" statement. When I drove the car this morning and turned the A/C the air was not hot. I turned the heat on and yes the air was very warm. The AC felt like room temperature air. Do i simply need to "recharge" the system with some R12? If so where do I begin? I've already located some R12 on craigslist.

Before you "recharge" you need to determine what the problem is. Do you know if the compressor clutch is engaging when you turn on the AC? Did the AC just quit working, or has it been out of service for a while?

[Sovereign]

The AC has not worked since I purchased the car about four months ago. When I switch from AC to heat there is a noise that sounds like the compressor is coming on. The blower works great and I commend the power of the heater Is there a different way to check the compressor clutch

If you look at the pulley on the front of the compressor with the engine running and the AC off, the center section on the pulley is stationary while the outer pulley is spinning. When the clutch engages, the center section spins (assuming yours is like the bottom photo):

http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=1CQ0J3JZ425F0ZP863&year=1981&make=MB&model=300-D-002&category=R&part=A%2FC+Compressor&appEngines=_any

[Sovereign]

The compressor clutch appears to be engaging. What is the next step?

[ispmaster]

Originally Posted by Sovereign

The compressor clutch appears to be engaging. What is the next step?

Next check the sight glass on the dryer/receiver. The freon level must not be too low if the A/C compressor clutch is engaging. If you see bubbles, you need to add freon.

[Sovereign]

How many cans of R12 will I need to 'recharge'? Is there a fill line?

[carnut]

The amount is also listed on the label underhood. I advise you to seek out someone to do this. The system must be evacuated prior to recharging. If low, theres a leak. The leak must be fixed before adding r 12. On this old of a car, Mercedes or whatever, the receiver/drier should be replaced as well. Adding r 12 without fixing the leak is like putting air at $30.00 a pound into a leaking tire.

[AMH]

Am I incorrect or did the '81 123 chassis still have the Type II ACC?

Type I was adjusted with two dials
Type II was adjusted with pushbuttons and the PITA servo
Type III used pushbuttons

Do a search under my username, there should be some information regarding the three types of acc

I agree with having a qualified mechanic check/repair the a/c. When a question arises "how much freon do I add" "do I need a set of gagues" etc it's time to stray away.