1989 240 DL
The heater in my car only puts out barely warm air. I adjusted the contol wire at the valve but it didn't help any. I don't know much about the system. Thermostat? Do I want to think about "gently" back flushing the heater core at the firewall connections? Is there a problem with the valve? I just replaced the lower hose to the heater core at the firewall. Had to replace the gasket at the water pump on the coolant bypass tube. It was warm then so we didn't use the heater. Not warm now though. Best guesses? Thanks.
The more I think about this, the thermostat moves up on my list.

Hi.
First, are you sure you have a filled cooling system -- what's the level in teh overflow reservoir? If it's empty, you probably have enough air in the system so that will prevent the needed amount of coolant from flowing through the heater core.

Second, what does your temperature gauge say about the coolant temperature? Your '89 has the infamous Temperature Compensation Board, but if we assume it's working right, is it reading normal temperature? If low, you could have a stuck-open thermostat -- thermostat's fail (it's happened to me) -- and then you won't get enough heat.

Finally, how do you know that you don't have a clogged heater core. The previous owner may have neglected the cooling system, or used hard water in the solutions, and you can have a ruined heater core.

Just some suggestions.
Good luck.

there is not enough coolant in the engine to allow circulatoin through the heater core. Probably not your answr, though, since you would have other symptoms.

When the HVAC blower fan is running, air is drawn through both the a/c evaporator coil and the heater core. The conditionin of the air into the cabin depends on how much hot coolant is going though the heater core and/or how often the a/c compressor is turning on.

In your case, the a/c is turned off, right? And you are getting plenty of air flow out the vents, right?

So it is up to getting hot coolant through the core. Let us assume that there is sufficient coolant to allow circulaton throughthe core. The problem would then be that coolant is not hot enough.

Have you checked the engine cooling system thermostat? Since your year has the temp compensation board, inadequate engine temp may be masked. Has the temp gauge been running below the 9:00 AM normal position?

The labor to check the thermostat is the same as that needed to replace it. So install a new one, 92C. I use Volvo thermostats, many on the BB use another brand.

In cold enough weather, an open engine thermostat will keep the engine temp from reaching its optimum running temp. Besides reducing cabin warming, the ECU sees "Low Temp" and adds additional fuel. My 1988 244 came to me with no thermostat at all. When I installed one, the temp ran normal and the miles per gallon went up.

If this doesn't help, post back and we'll find another angle.

Good Luck,

Bob

:>)

Bob,
In my 1989 240 DL the heater only puts out luke warm air. Lots of air flow. AC doesn't work so it isn't a factor. Changed thermostat, let car idle 10-15 minutes (instrument cluster is out for now on another issue) just luke warm air. Hose coming down to heater valve is hot. Hose that runs under the center console is hot also, but doesn't seem as hot. Recently the firewall to engine block hose gave out and I replaced it. Had to replace the gasket at the water pump for the coolant bypass tube also. Radiator was replaced last summer.
I am thinking that I hood the hoses together bypassing the valve to determine if it is the valve or the core? Doesn't look like it will be a lot of fun though.
I have seen on this site how to replace the valve with a "new style round one" from FCP Groton.
Any suggestions, helpful hints, better ideas, Volvo elves to do the work???

Hey John,
If you lose vacuum to operate the vent doors, I believe the system defaults to defrost mode.
You would have no air coming from the floor or recirculating vents. That would substantially cut down on heat coming into the car.
Just a thought before you tear into it. Check it out.
If that is the problem start by checking the condition of the small vacuum hose on
top of the engine. There a vacuum reservoir underneath the dash etc.

L.

I haven't had a vac line running through the firewall on my '87 240 for years. I get full hot/cold (no AC installed, but if I slide towards blue it cuts the heat), and I get plenty of airflow through the vents. If I want defrost, I close all the dash vents and peek through the small clear spot that appears on my windshield.
--
forums.turbobricks.com

likely to be a closed thermostate. try puting a new 1, or oil that one, worked for me!

i mean stuck open!