My 1988 300SE air conditioner is not working. Last week the heater wouldn't work So I have expereinced both no hot air and no cold air.
Today the heater is working not the air conditioner. Seems to be intermittent and certainly not the one I want when I want it. Can you help with what to look for
Thanks Brian

Brian
Kind of confusing what's going on.
Would you say that sometimes it blows hot air (even though you don't want it to, say you have it set at max cool and it blows hot air) and other times you actually want heat but it doesn't blow hot at all?
If you run the AC is the clutch coming on, or don't you know that?
Is the blower fan working OK, or is that screwed up too?
Is the engine getting up to operating temp or is that fluctuating up and down? Should run about 80 C.

Gilly

I have a similar problem, with the heater only. Some times the fan will work, sometimes not. The coolant temperature is normal and steady. Should I post a separate thread or follow this one?

Gilly- What does it mean when the engine temperature fluctuates rather than stay steady at 80 or 90C? What if it is not the thermostat?

Gilly: Thank you for the response on 1988 300 SE.
Inetermittently, when on A/C does not blow cold and I dont think clutch is engaging. When heat is on no hot air. Fan works and intermitently it also does not blow period at times, only time I noticed fan not blow was with heater and defroster on. I had a 300 D and when this occured it was a computer chip could it pssibly be same? Thanks Brian

Gilly:
Fogot to tell you Engine Temp is steady at 80. Just put in new Water pump and Thermostat. Is the wire that runs behind the shock to the engine a sensor that may be a problem I know we were working around it a lot getting everything back together? Brian

WOW! Everyone's hopping on this bandwagon!

Marty:
You may get more responses with your own thread. To me I would suspect the blower motor itself is bad, it should be tested (see if there is power to the motor in the failed state.

Rafi: Usually with a large fluctuation of the temp gauge, I suspect the thermostat. Possibly the thermostat that was installed is defective. What is the gauge fluctuating between (what are the high/low readings after driving the car for 10 minutes?)

Brian: You can have either the high pressure or low pressure switch shutting off the AC system, either because the pressures actually are high or low, or either the high presure switch or low pressure switch is bad. There is also what is called the "Klima" relay which may be bad, this is what controls the clutch. There could be a problem with the rpm sensor in the ac clutch also.
I'm not sure which engine sensor you are talking about, can you post a picture of it? Another possiblity is the "push button panel", this is the part in the dash which runs the ac, it's also the part with the buttons on it to activate the system. On the fan not working, you need to test is as I outlined for Marty; get it in a failed state and see if there is power going to the fan, if there is, then the fan is bad.
I'm not sure what computer chip you replaced in the 300D, usually we speak in terms of a component being replaced, not an individual chip, although some poster here do get right down to saving money by going into modules and replacing and resoldering things, more power to 'em if they have the time to invest in diagnosing and repairing circuit boards, it goes beyond what I like to do.
In regards to "heater is on but no hot air", what I usually think of is what's called the mono-watervalve. There is a rubber diaphragm in the mono-watervalve that can rip, which can cause either too much heat or no heat, basically the temp in the heater is no longer regulated at all. The part that rips in the water valve is replaceable as a seperate part, I can tell you how to inspect the water valve if you like, or use the search feature, I've explained it several times already here.

Gilly