Heater Blows Cold - Unusual Problem

My 1988 Mondial 3.2 heater is blowing cold air (ie. ambient air temp). This is after rebuilding the heater valve, the pump in the engine bay, checking various sensors, switches, swapping the computer controller with a good used one, etc.

But this is what has me stumped. It blows nice and hot hot when the engine is off (after having run the car for some time so the coolant is up to temp, and the key is in its on position). The engine pump motor hums nicely, the temperature control knob will cause the heater valve solenoid to pluck up and down as you turn it to the colder settings as it is supposed to, the heat goes off when you turn to cold and the ac solenoid clicks on. Ie. Everything works when the engine is (hot but) not running. If I turn the engine on, the heat blows out briefly and then reverts to ambient temps (ie. cold) again.

How can this be? Is there some sort of relay that is not functioning when the engine is running, even though I would have though the key in running position whether the engine is on or off is what would activate all the bits?

To rule out some other things, I also changed the engine thermostat which was due anyways, this made no difference, and I have bled the air out of the coolant repeatedly with the heater in its on position, with the engine cold and hot, all to no effect.

I have checked some old threads, and no one has this type of issue that presents only when the engine is running.

Anyone have some clues on what I might be missing?

 

I don't think that is possible with the way the pump mounts to its bracket. Will take a closer look.

 

Might have been more possible that the heater valve hoses were mixed up. Not sure I can tell which one should go where if I have mixed them up.

 

Checked the hoses for the pump and the valve, it does not look possible to have them mixed up. Good thought though.

Still completely stumped. Not sure what I can do to further diagnose this. Something must be preventing coolant flow to the heater core when the engine is on.

 

Thank you for thinking about this problem. I am getting the voltages noted at the heater valve connector.

 

It appears the shorter hose that connects to the bottom would not be able to reach the upper outlet, so I don't think mixing these up was possible. But who knows, maybe the shorter hose can be pulled out, when I say the shorter hose, the bottom one goes about 4 inches straight out and then through the body panel to who knows where. The top hose appears to turn up with about 87 inch of length and goes up somewhere behind the heater unit, I can not see where it actually connects.

 

I know you appear to have seen it all from prior threads, so add this to your list of unsolved mysteries. I will get to the bottom of it, but will probably remove the valve and check flows and such which I may not get to for a while, the driving season in Toronto has just started, and the good news is the ac works as it should!

 

Good question, I am not sure how the water flow actually routes from engine to radiator and heater core and back. I have never had the need to trace all these hoses before.

 

Is it possible I have some mega air lock in the coolant system, when I bleed I get very little air. But before I start dismantling things again and draining coolant etc. I thought I should check in on bleeding. For greater certianty, does one bleed cold (with the heat on?), or when the engine is running (and heater on?)? Or a bit of both, I am not sure if one bleeds while the engine is running whether that would suck more air in. I should know all this, but I have never had any bleeding problem in the past and I have probably done the rad and thermostat bleeds many times both cold and hot/running so I never gave it much thought before. But maybe for greater certainty it is worth doing carefully before going deeper.

 

The 1988 Mondial 3.2 has a small separate electrical pump interconnected to the colling system that provides some added help.

My current theory is that the spring in the electrovalve plunger unit might be shot or weak from age, and is not able to hold the plunger in place when the engine water pump increases the pressure. I recall the plunger pulls up to block heat when the car ignition is on (ie. always on 12 volts activates the solenoid and pull the plunger up to block coolant flow to the core, and snaps/releases the plunger down when the controls ask for heat and the solenoid voltage is cut to zero. Meaning if the voltage stopped or the solenoid fails it would fail in the plunger down - heat always on condition? If the plunger is down for heat in my case, maybe the spring force might be overcome by the engine water pump pressure if the spring is weak? Not sure I am describing this correctly.

I am thinking about this as although I rebuilt the plunger with the Europarts seal kit, but did not replace the plunger itself which has an internal spring. The spring action seemed fine, but maybe it has cycled on and off many time and lacks the holding power?

Of course I will have to remove the valve ( I really did not enjoy doing that, working under the dash is not easy on the back), maybe swap in a new plunger and can double check then the pipes were not somehow reversed. Not looking forward to having to make a mess with draining coolant again.

I did purchase a new OEM ancilliary pump with the correct part number (not the superceded pump # which fits more modern Ferrari's but has a different location of the wire connector on its body, my replacement is identical to that which was on the car). Maybe the polarity of the wires is somehow reversed and that pump is spinning the wrong direction inside? The electrical connectors seems to only go on one way, on the both the pump and electrovalve, but I am trying to come up with ideas as what weird things could be going on here.

 

It is harder to tell with the engine noise, but yes I put my hand on the valve unit and it appears to cycle when the temp is turned down as it should, but no heat produced. Engine off (with ignition on), and heat immediately comes out the vents. I would have thought electrical too, but the engine on verses off function shouldn't be affecting anything electrical, the key being in the on position activates the relevant circuits.

I am focussed on the electrovalve as the cultprit. I do have a spare one, that I rebuilt the plunger on as well, so I should be able to swap it in, and this should isolate if the old unit plunger spring was weak. Just have not found the time to drain the coolant and get at it yet, the car is running beautifully and I just put it on the road so I want to enjoy spring drives for a bit before tackling the project. I will report back if I have any luck.

 

Solved!

Based on teh Fchat prodding to fix this, I got at it today.

First, I used some SK hose clamps on the two lines, so I did not have to drain the coolant. I attach a pic of the SK tool number for those who want the size that is the right fit for theses smaller heater hoses.

Second, I removed the heater valve. On the bench, I dismantled it to inspect things carefully. It all look fine so I was still baffled. I then checked on the internet to see an exploded view of the plunger assembly, and sure enough, I had assembled it incorrectly. Double checked on old Mercedes sites that also use the same valve, and they all are the same way. I had the large washers and springs on the wrong side of the valve, and the valve when calling for hot would not have had enough reach to close the bypass pipe fully and with the pressure from the engine water pump running it probably pushed the pluger away further. I had taken a picture when I disassmebled, must have mixed up the visual at the time, stupid error. I reassembled things correctly, bench tested it for soledoid action and sealing and back in the car. Heater blows a furnace, and shuts off when ac is called for. Success!

I attach further pictures for those in the future who want to see the correct order of the washers and wave spring. Also there is a little notch on the solenoid holder, that aligns with the electricasl connector nub that is slightly below the flat surface, so make sure that is aligned correctly before tightening things back up.


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You know, I never did really understand how the water hoses circulate the water to the heater.

The top hose on the heater valve appears to connect to the heater box, it disappears into the plastic shroud, not sure how one would change that hose. It looks like a molded shaped hose, but there is no part num ber for this on any parts diagrams. The arrow on the heater valve suggests this hose is where the hot water enters the heater valve, but why is it coming from the heater box?

If the heater valve is open (ie. heat requested), then the water just goes out to the bottom hose? If valve closed, then heat is stuck in the heat exchanger?

The bottom hose on the valve goes through the body and I think goes to the large bottom radiator return pipe that goes back to the engine, but I am not sure, I have not been able to get a visual on where that bottom hose on the actually valve goes. Given the bottom valve pipe has a check valve, it is obvious the flow is in to the top and out the bottom, so the bottom hose returning back to the large return rad pipe makes sense.

The pump in the engine bay seems to take coolant from the engine, and pumps it up the left side of the engine bay and over to the right side, where the hose eventually disappears into the body for the run to the front of the car. It must eventually attach to the heater box, if I am ide ntifying the hose correctly it appears to clamp on to a copper pipe sticking out of the heater box. But if that is the water entry pipe into the heat exchanger, then the pipe going to the top valve would be the exit from the heat exchanger? Why would the valve be after the water goes through the heat exchanger, wouldn't it make sense that it controls the flow into the heat exchanger in the first instance?

All the exploded diagrams are incomplete and confusing, and in fact the Mondial T manual makes it look the like the heater valve pipes are reversed from the hoses I have just described.

Can anyone weigh in for posterity on which pipe does what. Part of why I am thinking about this is I may replace these heater hoses, that would no doubt be original. Makes no sense to do all the coolant hoses but leave these ones alone.

Has anyone actually replaced these hoses and therefore understands the routing and flow paths?

I also noticed that heater valve on its top metal parts is very hot to the touch, I presume the closed rest position of the valve always having 12 volts and keeping the valve closed would cause the solenoid to be energized constantly and throw off heat as a result? Why would they have designed it like this, seems like the solenoid life would be very low with constant current under a frequent closed no heat position of the valve.