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1989 Cotillion White Brougham
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321 Posts
Discussion Starter #1
That rather cryptic title may not have done my question justice. Here we go:

Let's say I have the heat set to 90 degrees. If I put the climate control system into LO, AUTO or HI, I can hear and feel the compressor engaging and disengaging, over and over, for as long as I keep it in those modes. If I use the ECON mode, of course it disengages the compressor, as it should.

I thought the compressor would only engage/disengage if it was needed? For example, if I have the defroster on, or if I need the air conditioning. Is this the way it's supposed to behave, running even with the heater on? My recollection of my father's 1986 Buick was that the compressor didn't engage if you had the heat on; you could leave it in AUTO (hence the term, "Auto").

Am I crazy?

Also, sometimes the heat won't come on unless I "trick" it: I have to engage the defroster, then switch to ECON. Otherwise, the fan will usually not begin blowing on its own. The air conditioning seems to work okay.

Any thoughts?


Thanks
 

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1994 Cadillac Fleetwood Brougham (some show and some go!)
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607 Posts
My 94 FW climate system still baffles me sometimes..... the compressor comes on for certain settings, even heat, to pull the moisture out of the air (I presume) and condition the air. I think that's what you are experiencing.

But what you may be further experiencing is low refridgerant in the ac system, causing weird pressures and the compressor to cycle, doesn't matter if you're in heat or cool, the compressor is still "called on" anyway. It's cycling due to low juice or a bad AC system component/sensor that deals with pressure.

I had low refridgerant when I got my 94 FW and added a bit and the cycling went away.

Good luck
 

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1989 Cotillion White Brougham
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321 Posts
Discussion Starter #3
The coolant level is okay, had it checked and filled recently. I wanted to replace the ECC head unit but the one I found on e-bay...well, an E-bay sniper got it at the very last second. We went back and forth several times, the bastard...

Oh, well. I'll find another one at some point and see if the ECC head unit is the reason my fan won't start up on its own sometimes. A minor inconvenience, but it's a 17 year old car, so...can't complain too much! (Although I do.) =P
 

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1987 Fleetwood Brougham
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239 Posts
I thought that's how it should work too, but in my '87, nope. In order to run heat without the A/C compressor, I put the thing in Econ mode. It seems to adjust the fan speed and even floor vents vs. dash vents based on temp. The heat actually works pretty damn well in these cars!
 

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1989 Cotillion White Brougham
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321 Posts
Discussion Starter #5
Yeah, I find that the heater doesn't warm up as quickly in my Brougham as it does in the Seville...a larger radiator, I suppose? The Seville would heat up very quickly! =D Meh.
 

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49 Posts
the compressor turns on and off in order to maintain the set degrees in temp...if u want 80 degrees the heat will come on,then when it gets too hot the a/c comes on and so forth to maintain that temp...
 

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1970 Sedan deVille hardtop
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595 Posts
No, the system is better designed than that. If it were using the AC to bring the temp back down, you'd feel the vents blow hot, then cold, then hot again. Doesn't do that though, blows a constant temp. Plus, my '70 with no AC charge andthe compressor unplugged keeps temp just fine.

The AC is run to keep the interior dehumidified. See, if the heat is on, there is a fair chance that it is raining or snowing outside. That means that everyone getting into the car brings in moisture. Just running the heat might keep the windows from fogging up, might not. Either way, you have higher humidity unless the AC is used to dry the air out.
We're actually covering HVAC systems in my applied thermodynamics class right now, and it is standard practice to run the air first through a cooling/dehumidifying section before heating it to keep humidity under controll.
 

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1989 Cotillion White Brougham
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321 Posts
Discussion Starter #8
The problem I have in particular is that the heat won't come on unless I engage the defroster, wait for the fan to spin up, the switch to another mode. Otherwise, the fan NEVER comes on, not in Lo, AUTO or HI.

So the sequence I use is as follows:

Wait for the car to warm up
Turn on the defroster and let the fan get up to speed
Switch to ECON for the rest of the ride.

If I engage the defroster but don't allow the fan to come to full speed, THEN switch, it kills it and doesn't come on. I thought that maybe the car wasn't warm enough to produce the desired heat, so AUTO wouldn't engage the fan until the temp was high enough. That's apparently not the case because I'll drive an hour and the heat still won't come on. UGH.
 
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