A/C does not blow cold 1988 300SE - PeachParts Mercedes-Benz Forum

florida Brian · #1 06-09-2008, 08:54 PM

Tool my 88 300 SE to have freon topped off as it did not seem to blow cold, cool but not cold. Mech put in 134 freon and could not get it to cool down. Told me I needed a Heater diaphram or maybe the heater switch as it was not shutting the heat down and thus heating up the A/C.
Pointed out to a part on the bulkhead passenger side. I don't feel heat on all the time in fact I feel cool air when just on economy vent and blowing outside air in. I am not confident in this diaganosis. I read the post on the electriacl test and lost me, can you help. Thanks, Brian

E150GT · #2 06-09-2008, 10:30 PM

put it on economy and set to cool and then unplug the electrical connection to the heater valve ( I cant think of the correct name of it) and the air will instantly become hot.

Hit Man X · #3 06-10-2008, 06:23 PM

134A isn't going to cut it in your climate.

dieseldiehard · #4 06-10-2008, 06:40 PM

Quote:

Originally Posted by E150GT

put it on economy and set to cool and then unplug the electrical connection to the heater valve ( I cant think of the correct name of it) and the air will instantly become hot.

A better test is to feel the temp of the hoses going into and out of the monovalve, that is the thing that the mech should have been pointing at. One hose carries hot water into the valve the other out, and the lines should not both be hot (actually neither should be really hot) after running only the AC for a while, if they are both hot than it sounds like he was right and its allowing water to flow thru, even a small trickle will "dilute" the cold air in the AC box. This is a fairly common problem, not a lot of AC issues related to a leaking mono valve its usually low gas due to leaks of the freon kind (=$$$)
Another test is clamping the hose off with a small C clamp or even vice grips to block the flow as a diagnostic.

youre stuck with 134 unless you want to pay for a conversion to R12 (used prior to 88) then there is the subject of other hydrocarbon gases but be warned using some of them are considered a rogue act (threads about the alternatives abound).

brewtoo · #5 06-10-2008, 09:40 PM

Quote:

Originally Posted by dieseldiehard

youre stuck with 134 unless you want to pay for a conversion to R12 (used prior to 88) then there is the subject of other hydrocarbon gases but be warned using some of them are considered a rogue act (threads about the alternatives abound).

Didn't this car use R12 originally?

jhodg5ck · #6 06-10-2008, 11:37 PM

Yup...R12 originally.. As stated above, even with everything working properly 134a isn't going to cut it in FL.

Checking the monovalve is Always a good idea! Just had a 560 in where the MV was leaking hot water into the heater core..replaced that and the AC got Quite a bit cooler..imagine that..!

You may take a look @ HC12 for a drop in replacement..hydrocarbon yes, but more efficient then even R12.

Jonathan

coatsworth · #7 06-11-2008, 12:10 PM

If you don't want to pay the price of R-12, I've heard of people using R-22 in their auto's, but they use different oil types so I'm not sure what kind of problems may result from that.

Hit Man X · #8 06-11-2008, 04:30 PM

Quote:

Originally Posted by coatsworth

If you don't want to pay the price of R-12, I've heard of people using R-22 in their auto's, but they use different oil types so I'm not sure what kind of problems may result from that.

What, $12-17/lb for three pounds is going to break the bank for R12?