# 1988 Chvy PU Heating/Defroster



## Bluewater09 (Jun 19, 2009)

I saw a post here from a while back about a truck problem so I thought I would give mine a try. I have a 1988 Chevy 1/2 ton PU. The heating sytsem works through these little devices called "actuatiors". Little motors really that move the air around the dash instaed of having the old pull cables that open and close vents. I am not able to get any air through the top of the dash to the window defroster. 

Does anybody have any experience with tracking this kind of problem. I have a diagram from Chevy that shows no less than three vents in the top end of the dash that have to operate to get the air to blow onto the windshield. 

There are two actuators. One lower and one upper.

Thanks


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## Drabdr (Nov 26, 2007)

Hello Bluewater! Welcome to TSG! We are delighted you chose this forum to post questions. 

Is there no air of any kind blowing out the top, or just during one setting? Has it ever worked, or is this something that just started recently?


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## Bluewater09 (Jun 19, 2009)

Good questions! I just bought the truck. I have owned it about a month or so. I am really excited about it. It has only 75,000 miles on it and is in great shape, no rust and the body is striaght.It was well taken car of and gargaed most of its life. 

It hasn't worked since I have owned it. I get heat and outside air on the floor but nothing through the two center vents in the middle of the dash, or through the defroster vent that blows on the windshield. 

I have removed the tape player and I can look inside to the middle of the dash. I can see a vent that is in the closed position. It is horizonal ( sealed) so it is preventing any air from comming up from the bottom.

The vent on the floor works. I can stick my hand up into it while pushing the cotrol and I can feel it closing and sealing off the air from blowing on the floor. 

AC doesn't work either.


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## daniel_b2380 (Jan 31, 2003)

Bluewater09 said:


> ....The heating sytsem works through these little devices called "actuatiors". Little *motors* really that move the air around the dash instaed of having the old pull cables that open and close vents. I am not able to get any air through the top of the dash to the window defroster.
> 
> Does anybody have any experience with tracking this kind of problem. I have a diagram from Chevy that shows no less than three vents in the top end of the dash that have to operate to get the air to blow onto the windshield.


bluewater,
i bought a number of '73 to '92 - mostly k's - but also a couple c's - to DISASSEMBLE / REASSEMBLE to put one k together to race in street-division bogging, [qualifies me a bit about them, i guess]

the very FIRST thing to check is to see if any of the ducting hoses have come 'off' their proper places - they just 'push-on' and 'pull-off' - no clamps - just a slight 'friction' holds them on

these 'actuators' you speak of are NOT 'little motors' as one usually thinks of motors, [being electrical] 
- they're actually VACUUM solenoids 
- so your problem, with it being an '88, is that more than likely - right at the ends of these vacuum hoses - they've cracked / split 
- there should be enough 'extra' hose to just cut about 1/2" to 5/8" off each end and just sliding the hose back on the fitting - rather than buying all new hoses 
- the hoses under the dash SHOULD be okay, under the hood will be the ones you need to thoroughly check
- also check the supply lines from the manifold to the vacuum reservoir, [should either be a roundish plastic unit about 4" or so in diameter -OR- it could be the larger unit about 8" or so in diameter -OR- it might even be a large 'juice' can about 4" in diameter and 10" or so tall]
- the MAIN vacuum supply fitting should be on the back of the manifold - between the carburator and the distributor - [assuming you have a 'real' chev engine instead of an olds engine]

- you may also need to check the adjustment of the actuator's 'anchoring' screw of the primary / main 'flapper valve'
- - which directs the air either 'down-to-the-floor' -OR- 'up-to-the-dash' vents and defroster vents
- and this control IS a cable-actuated one

- is the blower motor acually working at ALL the speeds? you might need to check the 'speed control' resister unit - it's IN the plenum chamber of the ac unit on the firewall - passenger side

- does the ac 'clutch' on the front of the compressor engage when you have someone turn it 'on' when you are watching / listening under the hood?
- you should hear it 'click' when it engages
- if not - check the fuse
- you should also hear a difference in the sound of the engine as the 'load' on it increases with the compressor engaging - IF it has a 'charge' of refrigerant

- with this being an '88 - more than likely you will also need to have the ac system 'recharged' - most likely it has 'leaked' out
- and while you are at it - i would just convert it over to the newer so-called 'greener / safer for the environment' refrigerant - [instead of paying the VERY expensive $$$$$ for the original freon type]
- they make 'kits' which are available at auto supply stores 
- you can 'do-it-yorself' if you are at all somewhat mechanically inclined


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## Bluewater09 (Jun 19, 2009)

Thanks. I thought they were electrical. The fact that they are vacum operated makes cracked hoses , or leaks a lot of sense. I'll take a look, but I haven't seen any ducting or vacume hoses under the dash anywhere, or even in the engine compartment. Then again, I hadn't looked for any. Those little suckers are expensive. The temp actuatur is $160.00. I am hopeful that I don't have to replace one. Blower motor works. The A/C clutch does not kick in, I can't hear it and there isn't any drop in RPMs to the engine. I have looked at some of the fuses, but not for A/C. I will check that. Thanks again. I have the day off and i'll poke around and see what I can find. 
This engine has throttle body fuel injection. I think I get a whopping 13 miles per gallon! Just as bad as my CJ-7, but I have a heck of a lot more room.


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## Bluewater09 (Jun 19, 2009)

I took a look. The actuators are electrical. They have wires going to them. They don't have vacume tubes. I am thinking that the actuator that runs the top vents is bad. I won't pay $160 for one. I have tried finding one on line used but I haven't had any luck so far. I live on a island, we have one wrecking yard here. I haven't checked for one there but ususally selection is pretty limited. Newer stuff rather than older stuff. 

Fuse for A/C is good. It is shared with the blower motor.


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## daniel_b2380 (Jan 31, 2003)

if you pay attention to the control there in the dash, you can see that there are TWO parts to the unit - the top lever is vacuum operated - the bottom one is the dual-stage cable operated part for the ducting of the air
[note: some of the '88, and up, 1500 series did use some 'revamped' control mechanisms - depending upon the assembly plant]

- the dash in those trucks isn't very difficult to remove - so that's a possibility
- you might also use a mirror and flashlight to be able to look up into under the dash - there are no 'lower-covers' on the bottom of the dash like there were on say the 'fancy' cars like a monte carlo / grand prix / riviera

- if you've removed the radio unit, you can also use the mirror and flashlight there also - and don't forget - when you re-install the radio unit, there is a brace on the BACK of the radio to help SUPPORT it, reduce vibration and keep the radio-control-shafts from bending - goes from the radio to the lower lip of the dash - unless you have the later series style radio unit - [whole unit just slides in]

also, you can remove the glove-box - which will let you see where the ducting-hoses branch off the inner plenum chamber - so you can check if any of those have come loose

another thought - maybe some of the 'little critters' have 'adopted' a new home - field mice and ground squirrels have been known to get into / through some very small holes - as you said it was sitting a lot - and built a nest somewhere in the plenums or ducting hoses.....

yeah, some high-lights of the cosmetic / minor mechanical changes
- the '73 to '80 were the square-nosed hoods - with one piece hood from the winshield - ['smack' a tree - lose a winshield also]
- the '81 to '87 1500 series had a rolled-nose - and had a 'plenum-chamber-intake-cover' between the hood and winshield
- the 1500 seies had a body style change in '88 - to that rounded slab-side compared to the earlier scalloped-side
- the 2500, 3500, and blazers and suburbans kept the scallop-side look up 'til '91

- chevy put fuel-injection on their units in '87 - although carburation was still available in the heavier series for a couple more years

trivia note: buy the hood-brace kit -OR- keep the hinges lubricated well - those hinges were strong - and when you add the 'binding factor' - the hoods 'kinked' in the middle clear across


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## Bluewater09 (Jun 19, 2009)

I didn't have time yesterday to work on this any further. Today is Fathers Day I'll have family stuff to do. I'll take another look, but all the controls on the dash for the heating and cooling and buttons. Toggle swithes. Push the topof the button and it moves the air to the upper part of the dash, except it doesn't work. Push the bottom part of the button and it direct the air lower on the dash or to the floor. I don't see any levers that would be working cables. 

I haven't removed the radio, but I will and see what I can see. I have removed the stock tape player, which is in center of the dash. I can see this "metal flap" that is horizontal, closed across the vent. No matter what button I push, it doesn't open. That flap is attached on one side to one of those actuators. That actuator, contols that flap, and a series of levers that open and close other flaps. I have a blow up of that section from the dealer showing all the parts. I can unclip the wire assembly from that actuator so I know it doesn't work when it is powered and not powered. I am thinking the actuator is bad, the flap is jammed and stuck shut, that kind of thing. I was going to wait and see if I could find a working actuator, before I pulled this one out. It is a tight space,working in it is difficult. I thought I'd put a working one back in after going through the hassel of removing the existing one.

Have agood day. I'll let you know what I figure out. 

I have greased the hood hinges. Where does one get more information about the hood -brace kit?


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## Bluewater09 (Jun 19, 2009)

I pulled that dash all apart this weekend. I had the glove box, tape player the radio, and the heater controls all pulled out. I have determined that the two little actuators are working. I can feel them vibrate a little when I work the controls. I believe that I have narrowed the problem down to the linkage. According to this blow up I have of that area the vent doors that control where the air goes are opened and closed with the mode actuator. The doors are all conected to each other. I can see the little levers working, but not very well. No matter what I took apart I could not gain access to them. I have one more thing to try. I belive the guts to the radio is under the dash near the floor. I think I can get up there if I remove it. There isn't a lot of room to work and its really difficult to see anything. But I need to get some air to the top of the dash. It's only blowing on the floor now.

Thanks for your interest again.


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## daniel_b2380 (Jan 31, 2003)

another thing you might consider is the 'screening' for the defroster - and WHAT can 'fall' or get 'stuffed' into them
- sometimes on purpose - 'set' something there to 'hold' it
- sometimes by accident - pens, pencils, etc - a child in the car, dad putting gas in the tank - [doesn't take long]

and see if there are any 'anchoring' screws that should be 'holding' those actuators in a specific postion that may have worked loose enough to let them be 'doing the moving' - instead of staying put to move a lever, whatever...


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